Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session KP1: Poster Session I (3:20 - 4:05pm) |
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Room: E Concourse |
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KP1.00001: STUDENT POSTER COMPETITION: COMPUTATIONAL |
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KP1.00002: Mesoscale Modeling of Marangoni Convection in Evaporating Colloidal Droplets Mingfei Zhao, Xin Yong In this work, we develop a three-dimensional free-energy-based multiphase lattice Boltzmann-Brownian dynamics model with thermal effects for elucidating particle dynamics in evaporating nanoparticle-laden droplets in the presence of Marangoni convection. The introduction of thermal effects enables the development of the 3D internal flow structures due to concomitant inhomogeneous evaporation at the droplet surface and thermal conduction inside the droplet. In particular, the model is capable of capturing thermal Marangoni flow along the surface of droplets and its interplay with the internal flow. We calculate the temperature field separately and consider the thermal effect as a forcing term in the lattice Boltzmann model. We first model non-evaporating droplets loaded with nanoparticles and the effects of temperature field on the flow structure. By implementing evaporation, we probe the self-assembly of nanoparticles inside the droplets or at the liquid-vapor interface. We analyze the microstructure of nanoparticle assemblies through radial distribution functions and structure factors. Our findings provide critical insights into the dynamics of nanoparticle self-assembly in evaporating fluid mass with Marangoni convection. [Preview Abstract] |
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KP1.00003: Relationships between development/decay of a vortex and its topology in different flow scales in an isotropic homogeneous turbulence Keisuke Yamamoto, Katsuyuki Nakayama Development or decay of a vortex in terms of the local flow topology has been shown to be highly correlated with its topological feature, i.e., vortical flow symmetry (skewness), in an isotropic homogeneous turbulence [K. Nakayama, Phys. Rev. Fluids (2017)]. Since a turbulent flow might include vortices in multi-scales, the present study investigates the characteristics of this relationships between the development or decay of a vortex and the vortical flow symmetry in several scales in an isotropic homogeneous turbulence in low Reynols number. Swirlity is a physical quantity of an intensity of swirling in terms of the geometrical average of the azimuthal flow, and represents the behavior of the the development or decay of a vortex in this study. Flow scales are decomposed into three scales specified by the Fourier coefficients of the velocity applying the band-pass filter. The analysis shows that vortices in the different scales have a universal feature that the time derivative of swirlity and that of the symmetry have high correlation. Especially they have more stronger correlation at their birth and extinction. [Preview Abstract] |
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KP1.00004: Computational Analysis of a Wells Turbine with Flexible Trailing Edges Kellis Kincaid, David MacPhee The Wells turbine is often used to produce a net positive power from an oscillating air column excited by ocean waves. It has been parametrically studied quite thoroughly in the past, both experimentally and numerically. The effects of various characteristics such as blade count and profile, solidity, and tip gap are well known. Several three-dimensional computational studies have been carried out using commercial code to investigate many phenomena detected in experiments: hysteresis, tip-gap drag, and post-stall behavior for example. In this work, the open-source code Foam-Extend is used to examine the effect of flexible blades on the performance of the Wells turbine. A new solver is created to integrate fluid-structure interaction into the code, allowing an accurate solution for both the solid and fluid domains. Reynolds-averaged governing equations are employed in a fully transient solution model. The elastic modulus of the flexible portion of the blade and the tip-gap width are varied, and the resulting flow fields are investigated to determine the cause of any performance differences. [Preview Abstract] |
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KP1.00005: Creations of a turbulent puff in a pipe flow with dilute microbubbles Kotaro Nakamura, Yuji Tasaka, Yuichi Murai We examined mutual interactions between a puff and microbubbles in a horizontal pipe flow at Re$=$1900. Forty trials to investigate flow status were performed at different perturbation amplitudes controlled to create puffs for both of single-phase and flows with dilute microbubbles. The maximum volume fraction of the bubbles is 0.018{\%}. The results indicated that adding microbubbles enhances puff creation, which means intensification of flow transition. It contradicts with the previous experimental findings that milky bubbly liquid provides delay of the flow transition. This difference may be due to local volume fraction; tiny amount of microbubbles accumulate in vortical structures of a puff, and the accumulated bubbles enhances the vortices. To estimate the accumulation numerically, bubble motion in a puff is calculated by Euler-Lagrange simulations. Force balance equation considering buoyancy, pressure gradient, added-mass, drag, and lift is solved by a one-way simulation, which is coupled with velocity fields of a puff obtained by DNS. Estimating the radial pair distribution function and the force balances in a puff, we indicated that microbubbles accumulate in a puff and the pressure gradient originated from the vortical structures is larger than the lift. [Preview Abstract] |
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KP1.00006: Control of three-dimensional waves on thin liquid films Ruben Tomlin, Susana Gomes, Greg Pavliotis, Demetrios Papageorgiou We consider a weakly nonlinear model for interfacial waves on three-dimensional thin films on inclined flat planes -- the Kuramoto---Sivashinsky equation. The flow is driven by gravity, and is allowed to be overlying or hanging on the flat substrate. Blowing and suction controls are applied at the substrate surface. We explore the instability of the transverse modes for hanging arrangements, which are unbounded and grow exponentially. The structure of the equations allows us to construct optimal transverse controls analytically to prevent this transverse growth. We also may consider the influence of transverse modes on overlying film flows, these modes are damped out if uncontrolled. We also consider the more physical concept of point actuated controls which are modelled using Dirac delta functions. We first study the case of proportional control, where the actuation at a point depends on the local interface height alone. Here, we study the influence of control strength and number/location of actuators on the possible stabilization of the zero solution. We also consider the full feedback problem, which assumes that we can observe the full interface and allow communication between actuators. Using these controls we can obtain exponential stability where proportional controls fail, and stabilize non-trivial solutions. [Preview Abstract] |
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KP1.00007: Linear Aspects of Stability in Flow Induced Oscillations of Cantilever Pipes: Application of a Popular Heuristic Algorithm Ullhas Hebbar, Abilash Krishnan, Ravikiran Kadoli This work studied linear aspects of flow induced oscillations in cantilever pipes, with an emphasis on the numerical method of solution adopted for the system of governing equations. The complex frequencies of vibration of the different characteristic modes of the system were computed as a function of the flow velocity, wherein multi-variable minimization was performed using the popular Nelder-Mead heuristic algorithm. Results for a canonical fluid-to-pipe mass ratio ($\beta )$ were validated with literature, and the evolution of frequencies was studied for different mass ratios. Additionally, the numerical scheme was implemented to compute critical conditions of stability for the cantilever system as a function of $\beta $. Finally, interesting aspects of the dynamics of the system were analyzed: the supposed `mode exchange' behavior, and an explanation for discontinuities observed in the critical conditions plotted as a function of $\beta $. In conclusion, the heuristic optimization based solution used in this study can be used to analyze various aspects of linear stability in pipes conveying fluid. [Preview Abstract] |
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KP1.00008: Brachistochrone curve of a fluid filled cylinder Srikanth Sarma, Sharan Raja, Pallab Sinha Mahapatra, Mahesh Panchangnula The brachistochrone curve for a non-dissipative particle tries to maximize inertia of the particle but for a fluid filled cylinder, increasing inertia would amount to high dissipative losses. Hence the trade off between inertia and dissipation plays a vital role in the dynamics of a fluid filled cylinder. This trade off manifests itself in the form of an integro-differential equation governing the angular acceleration of the cylinder. Here, we compute the brachistochrone curve using optimal control principles and investigate the effect of the fore mentioned trade off on the deviation of the brachistochrone curve from that of a non-dissipative particle. Also, we investigate the effects of the non-dimensional parameters of the problem on the shape of the brachistochrone curve. We analyze the dissipation rate during the cylinder's motion and show that energy based arguments don't hold good for a fluid filled cylinder. We then analyze the stability of the time varying fluid flow in the cylinder and find an admissible region for the terminal point which would ensure the stability of the fluid flow as the cylinder rolls over the brachistochrone curve. [Preview Abstract] |
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KP1.00009: STUDENT POSTER COMPETITION: EXPERIMENTAL |
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KP1.00010: A Unique Facility for the Study of Transient Single-Species Annular Flow Near Total Film Evaporation Roman Morse A new facility was built for the study of transient effects in two-phase vertical annular flow near dry out. The facility uses two water/glycol loops and two 10 kW heat pumps to vaporize and condense the working fluid in the annular flow experiment, R-245fa. The annular flow is created by mixing a steady flow of slightly superheated vapor refrigerant with a steady flow of subcooled liquid refrigerant in a junction specifically designed to minimize droplet entrainment. In a separate tank, saturated refrigerant is heated to generate additional vapor to add to the steady state vapor to create transient conditions. Trains of vapor pulses can be created with controlled amplitude and frequency. The effects of the transient flow on dry out are characterized in a test section 110 diameters downstream of the vapor-liquid mixing junction. The test section consists of 14 transparent windows, which are coated with conductive fluorine-doped tin oxide. Current is passed through each of the windows, providing up to 1.4 kW of additional heating power to create film evaporation, or dry out conditions. The transparent windows also allow for simultaneous laser-based film-thickness and wall-temperature measurements. [Preview Abstract] |
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KP1.00011: Reynolds number scalability of bristled wings performing clap and fling Skyler Jacob, Vishwa Kasoju, Arvind Santhanakrishnan Tiny flying insects such as thrips show a distinctive physical adaptation in the use of bristled wings. Thrips use wing-wing interaction kinematics for flapping, in which a pair of wings clap together at the end of upstroke and fling apart at the beginning of downstroke. Previous studies have shown that the use of bristled wings can reduce the forces needed for clap and fling at Reynolds number (Re) on the order of 10. This study examines if the fluid dynamic advantages of using bristled wings also extend to higher Re on the order of 100. A robotic clap and fling platform was used for this study, in which a pair of physical wing models were programmed to execute clap and fling kinematics. Force measurements were conducted on solid (non-bristled) and bristled wing pairs. The results show lift and drag forces were both lower for bristled wings when compared to solid wings for Re ranging from 1-10, effectively increasing peak lift to peak drag ratio of bristled wings. However, peak lift to peak drag ratio was lower for bristled wings at Re$=$120 as compared to solid wings, suggesting that bristled wings may be uniquely advantageous for Re on the orders of 1-10. Flow structures visualized using particle image velocimetry (PIV) and their impact on force production will be presented. [Preview Abstract] |
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KP1.00012: Effect of Seed Density on Splash Cup Seed Dispersal Patrick Wigger, Rachel Pepper Splash cup plants are plants that utilize a small, mm-sized cup filled with seeds as a method of seed dispersal. The cup uses kinetic energy of an incident raindrop in order to project the seeds away from the plant up to 1 meter. The dispersal distance is important to ensure the offspring are not clustered too tightly to the parent plant. It has previously been found that a cup angle of 40 degrees to the horizontal is optimal for maximum dispersal of water from cups with no seeds. In this study we examine if the 40 degree cup is optimal for cups containing seeds with varying densities. We released uniform water drops above 5.0 mm 3D printed models of splash cups, using 1.0 mm plastic and glass microspheres of varying densities to simulate seeds. We observed the dispersal characteristics of each bead type by measuring the final seed locations after each splash, and by recording high speed video to determine the angle and velocity of the seeds as they exited the cup. [Preview Abstract] |
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KP1.00013: Large scale structures of a turbulent Rayleigh-Bénard convection in a liquid metal layer confined by a moderate aspect ratio box Megumi Akashi, Yuji Tasaka, Takatoshi Yanagisawa, Yuichi Murai, Tobias Vogt, Sven Eckert We report laboratory experiments of Rayleigh-Bénard convection with a liquid metal, Prandtl number Pr $=$ 0.03, in a rectangular cell at a moderate aspect ratio of 5. The Rayleigh number, Ra, was varied in a range from 7.9 × 10$^{\mathrm{3}}$ to 3.5 × 10$^{\mathrm{5}}$ in which the regime of thermal turbulence regime is to be expected. Multiple horizontal velocity profiles were measured in the fluid layer by ultrasonic velocity profiling. The reconstruction of the flow pattern elucidated the occurrence of large scale structures with periodic oscillations. An increasing Ra number causes a transition from a quasi-two-dimensional roll-like structure to a three-dimensional cell-like structure. The transition of the flow structure passes several unstable intermediate regimes accompanied by a stepwise increase of the horizontal scale. For explaining the increase in the horizontal scale, we suggest a model relying on observed Ra dependences of the oscillation frequency and the typical flow velocity of the large scales. Moreover, we have found that the morphology of the roll-like structure can be understood by evaluating the effective viscosity and diffusivity on the basis of turbulent fluctuations. [Preview Abstract] |
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KP1.00014: Stress fields in soft material induced by injection of highly-focused microjets Yuta Miyazaki, Nanami Endo, Sennosuke Kawamoto, Akihito Kiyama, Yoshiyuki Tagawa Needle-free drug injection systems using high-speed microjets are of great importance for medical innovations since they can solve problems of the conventional needle injection systems. However, the mechanical stress acting on the skin/muscle of patients during the penetration of liquid-drug microjets had not been clarified. In this study we investigate the stress caused by the penetration of microjets into soft materials, which is compared with the stress induced by the penetration of needles. In order to capture high-speed temporal evolution of the stress field inside the material, we utilized a high-speed polarized camera and gelatin that resembles human skin. Remarkably we find clear differences in the stress fields induced by microjets and needles. On one hand, high shear stress induced by the microjets is attenuated immediately after the injection, even though the liquid stays inside the soft material. On the other hand, high-shear stress induced by the needles stays and never decays unless the needles are entirely removed from the material. [Preview Abstract] |
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KP1.00015: Growth of finite amplitude disturbances in pipe flow with sudden expansion Shun Ishizaka, Benoît Lebon, Jorge Peixinho, Yuji Tasaka, Yuichi Murai Visualizations of the flow in circular pipe with a sudden expansion with subcritical transition were performed using reflective flakes and dye to elucidate growth of finite amplitude disturbances. At five inlet pipe diameters upstream of the expansion, disturbances were introduced through a small hole from the pipe wall in the form of a continuous jet or an alternation of injection and suction. Localized turbulent patches formed when the disturbance amplitude exceeded a critical value of the control parameter depending on the Reynolds numbers. For the crossflow jet, the duration of turbulent patches at fixed downstream point is related to the velocity ratio of the mean jet velocity to the bulk velocity. By injection disturbances with velocity of around 30{\%} of main flow, turbulent patches formed intermittently and a response delay of the patch formation was observed. For synthetic jet, turbulent patches are formed depending on the driving frequency, which is around 1 Hz. The synthetic jet initiates turbulent patches through the growth of a wavy disturbance in the flow, that amplifies and breaks, further downstream than in the cases of the crossflow jet. Overall, these results suggest the existence of different mechanisms for the development of turbulent patches [Preview Abstract] |
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KP1.00016: Enhancement of focused jets by using surface microbubbles Ryosuke Yukisada, Akihito Kiyama, Xuehua Zhang, Yoshiyuki Tagawa Focused liquid jets are important for various key technologies, such as material deposition and automated pipetting. It has been challenging to create high speed jets of viscous liquids. Our latest work showed that it is possible to generate viscous jets by applying sudden acceleration to the liquid (Onuki et al., J. J. Multi. Flow, 2015). It was observed that under certain conditions cavitation bubbles form in the liquid, making important contribution to the increment of jet velocity (Kiyama et al., JFM, 2016). The increased velocity depends on the maximum size of expanding bubbles. Thus, for controlling the velocity of focused jets, it is crucial to control the bubble expansion. In this study, we investigate the effects of surface microbubbles on the focused jets. Before the impact is performed, the microbubbles are produced on an inner wall of the liquid container by using water-ethanol exchange technique. We experimentally measure the jet velocity and bubble motion utilizing a high-speed camera. It is found that surface microbubbles expand upon the impact, enhancing the increment of jet velocity under the conditions that do not trigger cavitation inception in the bulk liquid. [Preview Abstract] |
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KP1.00017: High-speed micro-droplet impact on a super-heated surface Yuta Fujita, Tuan Tran, Yoshiyuki Tagawa, Yanbo Xie, Chao Sun, Detlef Lohse In this study, we experimentally show that the condition for micro-droplets to splash depends on the temperature of the surface on which the droplets impact. We vary droplet diameter (30$\sim$120 $\mu$m) and surface temperature (20$\sim$500$^{\circ}$C). For an impacting droplet, splashing becomes possible for high surface temperature $T>$160$^{\circ}$C and Weber number $We>$100. In contrast, at low surface temperature $T<$140$^{\circ}$C, no splash was observed up to the maximum Weber number in our experiments, i.e. $We\sim$7,000. Our results show that the criteria for splashing of micro-droplets may be different from those of milli-sized droplets, in particular when the impacted surface is heated. [Preview Abstract] |
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KP1.00018: Experimental Measurement of Small Scale Multirotor Flows Jacob Connors, Joseph Weiner, John-Michael Velarde, Mark Glauser Work is being done to create a multirotor Unmanned Air Vehicle (UAV) based anemometer system that would allow for measurement of velocity and spectra in the atmospheric boundary layer. The flow from the UAV’s rotors will impact such measurements and hence must be filtered. This study focuses on measuring the fluctuations of the velocity field in the flow both above and below various UAVs to determine first, the feasibility of the creation of the filter, and second, the optimal placement of the system on the body of the UAV. These measurements are taking place in both Syracuse University’s subsonic wind tunnel and Skytop Turbulence Lab’s Indoor Flow Lab. Constant Temperature Anemometry is being used to measure these velocity field fluctuations across a variety of UAVs with differing characteristics such as size, number of propellers, and rotor blade type. The data from these experiments is being used to define a method to estimate the filter band required to isolate noise from wake effects, and determine ideal sensor placement based on characteristics of the vehicle’s design alone. [Preview Abstract] |
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KP1.00019: Vortex topology of rolling and pitching wings Kyle Johnson, Brian Thurow, Kevin Wabick, James Buchholz, Randall Berdon A flat, rectangular plate with an aspect ratio of 2 was articulated in roll and pitch, individually and simultaneously, to isolate the effects of each motion. The plate was immersed into a Re = 10,000 flow (based on chord length) to simulate forward, flapping flight. Measurements were made using a 3D-3C plenoptic PIV system to allow for the study of vortex topology in the instantaneous flow, in addition to phase-averaged results. The prominent focus is leading-edge vortex (LEV) stability and the lifespan of shed LEVs. The parameter space involves multiple values of advance coefficient $J$ and reduced frequency $k$ for roll and pitch, respectively. This space aims to determine the influence of each parameter on LEVs, which has been identified as an important factor for the lift enhancement seen in flapping wing flight. A variety of results are to be presented characterizing the variations in vortex topology across this parameter space. [Preview Abstract] |
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KP1.00020: Effect of varying solid membrane area of bristled wings on clap and fling aerodynamics in the smallest flying insects Mitchell Ford, Vishwa Kasoju, Arvind Santhanakrishnan The smallest flying insects with body lengths under 1.5 mm, such as thrips, fairyflies, and some parasitoid wasps, show marked morphological preference for wings consisting of a thin solid membrane fringed with long bristles. In particular, thrips have been observed to use clap and fling wing kinematics at chord-based Reynolds numbers of approximately 10. More than 6,000 species of thrips have been documented, among which there is notable morphological diversity in bristled wing design. This study examines the effect of varying the ratio of solid membrane area to total wing area (including bristles) on aerodynamic forces and flow structures generated during clap and fling. Forewing image analysis on 30 species of thrips showed that membrane area ranged from 16{\%}-71{\%} of total wing area. Physical models of bristled wing pairs with ratios of solid membrane area to total wing area ranging from 15{\%}-100{\%} were tested in a dynamically scaled robotic platform mimicking clap and fling kinematics. Decreasing membrane area relative to total wing area resulted in significant decrease in maximum drag coefficient and comparatively smaller reduction in maximum lift coefficient, resulting in higher peak lift to drag ratio. Flow structures visualized using PIV will be presented. [Preview Abstract] |
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KP1.00021: An Experimental Comparison Between Flexible and Rigid Airfoils at Low Reynolds Numbers Jaylon Uzodinma, David MacPhee This study uses experimental and computational research methods to compare the aerodynamic performance of rigid and flexible airfoils at a low Reynolds number throughout varying angles of attack. This research can be used to improve the design of small wind turbines, micro-aerial vehicles, and any other devices that operate at low Reynolds numbers. Experimental testing was conducted in the University of Alabama's low-speed wind tunnel, and computational testing was conducted using the open-source CFD code OpenFOAM. For experimental testing, polyurethane-based (rigid) airfoils and silicone-based (flexible) airfoils were constructed using acrylic molds for NACA 0012 and NACA 2412 airfoil profiles. Computer models of the previously-specified airfoils were also created for a computational analysis. Both experimental and computational data were analyzed to examine the critical angles of attack, the lift and drag coefficients, and the occurrence of laminar boundary separation for each airfoil. Moreover, the computational simulations were used to examine the resulting flow fields, in order to provide possible explanations for the aerodynamic performances of each airfoil type. [Preview Abstract] |
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KP1.00022: Enabling University Satellites to Travel to the Moon and Beyond Grace Siy, Richard Branam Electric propulsion is a method of creating thrust for space exploration that requires less propellant than traditional chemical rockets by producing much higher exhaust velocities, and subsequently costing less. Currently, such forms of propulsion are unable to generate the vast amounts of thrust that traditional thrusters do, thus research is being done in the area. The focus of this project is Hall Effect thrusters, a specific type of ion propulsion. The distinctive feature of these thrusters are magnets which capture the electrons from the cathode. These electrons ionize the propellant gas and then interact with the present electric field to accelerate the resulting ions, generating thrust. The objectives of this project include building two Hall thrusters with different magnet configurations, collecting performance data, and testing with a Faraday probe that directly measures current density. The first magnet configuration will be a conventional Hall Effect thruster arrangement, while the second thruster's magnets are arranged to create a significantly stronger magnetic field. The performance data and Faraday probe results will be used to determine the level of improvement between the thrusters. The goal is to integrate a Hall Effect propulsion system into the university's Cube-Sat program. [Preview Abstract] |
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KP1.00023: DFD POSTERS |
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KP1.00024: Testing Iodine as a New Fuel for Cathodes Harley Glad, Richard Branam, Jim Rogers, Matthew Warren, Connor Burleson, Grace Siy The objective of this research is to demonstrate the viability of using iodine as an alternative space propulsion propellant. The demonstration requires the testing of a cathode with xenon and then the desired element iodine. Currently, cathodes run on noble gases such as xenon which must be stored in high pressure canisters and is very expensive. These shortcomings have led to researching possible substitutes. Iodine was decided as a suitable candidate because it's cheaper, can be stored as a solid, and has similar mass properties as xenon. In this research, cathodes will be placed in a vacuum chamber and operated on both gases to observe their performance, allowing us to gain a better understanding of iodine's behavior. Several planned projects depend on the knowledge gained from this project, such as larger scaled tests and iodine fed hall thrusters. The tasks of this project included protecting the stainless-steel vacuum chamber by gold plating and Teflon\textregistered coating, building a stand to hold the cathode, creating an anode resistant to iodine, and testing the cathode once setup was complete. The successful operation of the cathode was demonstrated. However, the experimental setup proved ineffective at controlling the iodine flow. Current efforts are focused on this problem. [Preview Abstract] |
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KP1.00025: Atmospheric Infrasound during a Large Wildfire. Alexis Vance, Brian Elbing Numerous natural and manmade sources generate infrasound, including tornado producing storms, human heart, hurricanes, and volcanoes. Infrasound is currently being studied as part of Collaboration Leading Operational UAS Development for Meteorology and Atmospheric Physics (CLOUD MAP), which is a multi-university collaboration focused on development and implementation of unmanned aircraft systems (UAS) and integration with sensors for atmospheric measurements. To support this effort a fixed infrasonic microphone located in Stillwater, Oklahoma has been monitoring atmospheric emissions since September of 2016. While severe storm systems is the primary focus of this work, the system also captures a wide range of infrasonic sources from distances in excess of 300 miles due to an acoustic ceiling and weak atmospheric absorption. The current presentation will focus on atmospheric infrasound observations during a large wildfire on the Kansas-Oklahoma border that occurred between March 6-22, 2017. [Preview Abstract] |
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KP1.00026: Amplitude Death Behaviour of Coupled Thermoacoustic Oscillators. Nevin Thomas, Sirshendu Mondal, Samadhan A. Pawar, R.I. Sujith Amplitude death(AD) phenomenon can be utilized to develop a relatively simple technique which can be used to stop the unwanted high amplitude oscillations in thermoacoustic systems resulting from thermoacoustic instabilities. Here, we use a numerical model of the prototypical thermoacoustic system, Rijke tube, to systematically investigate the AD phenomenon in such systems. Bifurcation from the limit cycle oscillations which prevail in the uncoupled oscillators to AD is noted and the regions of AD are identified. We examine the effect of time-delay and dissipative couplings on the system of two Rijke tubes in cases where they are symmetrically and asymmetrically coupled. We could observe the cessation of oscillations in both the cases for appropriate combinations of coupling strengths, delay time and detuning. The relative ease of attaining AD when both the couplings are applied simultaneously is inferred from the results. The route from phase drift to synchronization to AD is seen when the dissipative coupling strength is incremented in steps. In the presence of strong enough coupling, AD was observed even when oscillators of dissimilar amplitude were coupled, while a significant reduction in amplitude was observed when coupling strength was not enough to attain AD. [Preview Abstract] |
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KP1.00027: Forced synchronization and asynchronous quenching in a thermo-acoustic system Sirshendu Mondal, Samadhan A Pawar, Raman Sujith Forced synchronization, which has been extensively studied in theory and experiments, occurs through two different mechanisms known as phase locking and asynchronous quenching. The latter indicates the suppression of oscillation amplitude. In most practical combustion systems such as gas turbine engines, the main concern is high amplitude pressure oscillations, known as thermo-acoustic instability. Thermo-acoustic instability is undesirable and needs to be suppressed because of its damaging consequences to an engine. In the present study, a systematic experimental investigation of forced synchronization is performed in a prototypical thermo-acoustic system, a Rijke tube, in its limit cycle operation. Further, we show a qualitatively similar behavior using a reduced order model. In the phase locking region, the simultaneous occurrence of synchronization and resonant amplification leads to high amplitude pressure oscillations. However, a reduction in the amplitude of natural oscillations by about 78$\%$ of the unforced amplitude is observed when the forcing frequency is far lower than the natural frequency. This shows the possibility of suppression of the oscillation amplitude through asynchronous quenching in thermo-acoustic systems. [Preview Abstract] |
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KP1.00028: Shear Flow Instabilities and Droplet Size Effects on Aerosol Jet Printing Resolution Guang Chen, Yuan Gu, Daniel Hines, Siddhartha Das Aerosol Jet printing (AJP) is an additive technology utilizing aerodynamic focusing to produce fine feature down to 10 micrometers that can be used in the manufacture of wearable electronics and biosensors. The main concern of the current technology is related to unstable printing resolution, which is usually assessed by effective line width, edge smoothness, overspray and connectivity. In this work, we perform a 3D CFD model to study the aerodynamic instabilities induced by the annular shear flow (sheath gas flow or ShGF) trapped with the aerosol jet (carried gas flow or CGF) with ink droplets. Extensive experiments on line morphology have shown that by increasing ShGF, one can first obtain thinner line width, and then massive overspray is witnessed at very large ShGF/ CGF ratio. Besides the fact that shear-layer instabilities usually trigger eddy currents at comparatively low Reynolds number ~600, the tolerance of deposition components assembling will also propagate large offsets of the deposited feather. We also carried out detailed analysis on droplet size and deposition range on the printing resolution. This study is intended to come up with a solution on controlling the operating parameters for finer printed features, and offer an improvement strategy on next generation. [Preview Abstract] |
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KP1.00029: Parametric Study of the the Train of Frozen Boxcars Model for Fluidic Harvesters Amir Danesh-Yazdi, Oleg Goushcha, Niell Elvin, Yiannis Andreopoulos One of the challenges that arises in the study of fluid-structure interactions is the development and application of simple mathematical models that properly capture the behavior of both media due to the inherently coupled nature of the physical problem. If, however, the typical two-way interaction between the fluid and solid can be effectively reduced to a one-way coupling for a certain flow case, the modeling of the fluid-structure interaction can be greatly simplified. In this talk, one such model, the Train of Frozen Boxcars (TFB) is developed for piezoelectric fluidic harvesters. The TFB approach involves the advection of several boxcars of different amplitudes, widths and separations as a model for the fluidic force acting on the beam. For the single vortex case, the TFB model is able to predict the average harvested power within 13\% of the experimental value. A parametric study of this model is also conducted to observe the influence of five boxcar parameters on the power output from the harvester: number of boxcars, boxcar amplitude, width, separation from the following boxcar and advection speed. Further development of this model would allow for the prediction of the power output of stiff piezoelectric harvesters in vortex and potentially even turbulent flows. [Preview Abstract] |
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KP1.00030: Wetting of silicone oil onto a cell-seeded substrate Yongjie Lu, Yau Kei Chan, Youchuang Chao, Ho Cheung Shum Wetting behavior of solid substrates in three-phase systems containing two immiscible liquids are widely studied. There exist many three-phase systems in biological environments, such as droplet-based microfluidics or tamponade of silicone oil for eye surgery. However, few studies focus on wetting behavior of biological surfaces with cells. Here we investigate wetting of silicone oil onto cell-seeded PMMA sheet immersed in water. Using a simple parallel-plate cell, we show the effect of cell density, viscosity of silicone oil, morphology of silicone oil drops and interfacial tension on the wetting phenomenon. The dynamics of wetting is also observed by squeezing silicone oil drop using two parallel plates. Experimental results are explained based on disjoining pressure which is dependent on the interaction of biological surfaces and liquid used. These findings are useful for explaining emulsification of silicone oil in ophthalmological applications. [Preview Abstract] |
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KP1.00031: Swimming in Semi-Synthetic Mucus Louis Rogowski, Benjamin Woodruff, Amanda Liew, Richard Burns, Jamel Ali, Hoyeon Kim, MinJun Kim Leveraging the fluid properties of human mucus is instrumental to perfecting artifical in vivo microscale swimming. Fiber networks, composed of mucin proteins, are the primary component contributing to mucus's viscoelastic properties. In addition to creating extreme bulk fluid properties, the fibers can cause microparticles to become entangled. Through experimentation, it was determined that magnetic three bead microrobotic swimmers are incapable of translational motion below a 7 Hz rotating magnetic field frequency. At higher mucus concentrations, three bead swimmers are tougher to form due to mucin fiber interference. However, entanglements with fibers allow two bead swimmers and single particles to be capable of translational motion; which is otherwise not possible in Newtonian fluids. Two bead swimmers have been demonstrated to be consistently controllable and perform well in even high mucus concentrations. Single particles have been observed to occasionally form mucin tails, creating a hybrid microswimmer. These novel mucus interactions allow for increased adaptability of microswimmers and provide a better understanding of in vivo fluid dynamics. [Preview Abstract] |
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KP1.00032: Copepod Behavior Response in an Internal Wave Apparatus D.R. Webster, S. Jung, K.A. Haas This study is motivated to understand the bio-physical forcing in zooplankton transport in and near internal waves, where high levels of zooplankton densities have been observed \textit{in situ}. A laboratory-scale internal wave apparatus was designed to create a standing internal wave for various physical arrangements that mimic conditions observed in the field. A theoretical analysis of a standing internal wave inside a two-layer stratification system including non-linear wave effects was conducted to derive the expressions for the independent variables controlling the wave motion. Focusing on a case with a density jump of 1.0 $\sigma _{\mathrm{t}}$, a standing internal wave was generated with a clean interface and minimal mixing across the pycnocline. Spatial and frequency domain measurements of the internal wave were evaluated in the context of the theoretical analysis. Behavioral assays with a mixed population of three marine copepods were conducted in control (stagnant homogeneous fluid), stagnant density jump interface, and internal wave flow configurations. In the internal wave treatment, the copepods showed an acrobatic, orbital-like motion in and around the internal wave region (bounded by the crests and the troughs of the waves). Trajectories of passive, neutrally-buoyant particles in the internal wave flow reveal that they generally oscillate back-and-forth along fixed paths. Thus, we conclude that the looping, orbital trajectories of copepods in the region near the internal wave interface are due to animal behavior rather than passive transport. [Preview Abstract] |
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KP1.00033: An Integral Equation Method Coupling with Variational Approach for Studying Coarse-Grained Lipid Dynamics Szu-Pei Fu, Shidong Jiang, Andreas Kl{\"o}ckner, Rolf Ryham, Matt Wala, Yuan-Nan Young In macroscopic model, the well-known Helfrich membrane model has been extensively utilized as it captures some macroscopic physical properties of a lipid bilayer membrane. However, some phenomena such as membrane fusion and micelle formation cannot be described in this macroscopic framework. Yet the immense molecular details of a lipid bilayer membrane are impossible to be included in a plausible physical model. Therefore, in order to include the salient molecular details, we study the dynamics of coarse-grained lipid bilayer membrane using Janus particle configurations to represent collections of lipids These coarse-grained lipid molecules interact with each other through an action field that describes their hydrophobic tail-tail interactions. For this action potential, we adopt the integral equation method on solving energy minimizer with specific boundary condition on each Janus particle. Both the QBX (quadrature by expansion) and fhe fast multipole method (FMM) are used to efficiently solve the integral equation. We also examine the numerical accuracy and qualitative observation from large system simulations. [Preview Abstract] |
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KP1.00034: Modeling hydrodynamic effects on choanoflagellate feeding Christian Oakes, Dr. Hoa Hguyen, Dr. Mimi Koehl, Dr. Lisa Fauci Choanoflagellates are unicellular organisms whose intriguing morphology includes a set of collars/microvilli emanating from the cell body, surrounding the beating flagellum. As the closest living relative to animals, they are important for both ecological and evolutionary studies. Choanoflagellates have three unicellular types: slow swimmers, fast swimmers, and thecate (attached to a surface by a stalk). Each has different morphology and feeding rate. We use the method of regularized Stokeslets to simulate cell-fluid interactions of each type and show the hydrodynamic effects on the amount and directions of fluid flow toward the collar. After validating the swimming speeds of our models with experimental data, we calculate the rate of flow across a capture zone around the collar (flux). This sheds light on how each morphological aspect of the cell aids in bacteria capture during feeding. Among the three types, the thecate cells have the largest average flux values, implying that they take advantage of the nearby surface by creating eddies that draw bacteria into their collar for ingestion. [Preview Abstract] |
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KP1.00035: Gravity effects on wind-induced flutter of leaves Nickalaus Clemmer, Karsten Kopperstad, Tomas Solano, Kourosh Shoele, Juan Ordonez Wind-Induced flutter of leaves depends on both wind velocity and the gravity. To study the gravitational effects on the oscillatory behavior of leaves in the wind, a wind tunnel that can be tilted about the center of the test section is created. This unique rotation capability allows systematic investigation of gravitational effects on the fluttering response of leaves. The flow-induced vibration will be studied for three different leaves at several different tilting angles including the wind travels horizontally, vertically downward and vertically upward. In each situation, the long axis of a leaf is placed parallel to the wind direction and its response is studied at different flow speed. Oscillation of the leaf is recorded via high-speed camera at each of setup, and the effect of the gravity on stabilizing or destabilizing the fluttering response is investigated. [Preview Abstract] |
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KP1.00036: Proper Orthogonal Decomposition and Dynamic Mode Decomposition in the Right Ventricle after Repair of Tetralogy of Fallot Amanda Mikhail, Lyes Kadem, Giuseppe Di Labbio Tetralogy of Fallot accounts for 5\% of all cyanotic congenital heart defects, making it the most predominant today. Approximately 1660 cases per year are seen in the United States alone. Once repaired at a very young age, symptoms such as pulmonary valve regurgitation seem to arise two to three decades after the initial operation. Currently, not much is understood about the blood flow in the right ventricle of the heart when regurgitation is present. In this study, the interaction between the diastolic interventricular flow and the regurgitating pulmonary valve are investigated. This experimental work aims to simulate and characterize this detrimental flow in a right heart simulator using time-resolved particle image velocimetry. Seven severities of regurgitation were simulated. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) revealed intricate coherent flow structures. With regurgitation severity, the modal energies from POD are more distributed among the modes while DMD reveals more unstable modes. This study can contribute to the further investigation of the detrimental effects of right ventricle regurgitation. [Preview Abstract] |
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KP1.00037: Fluid Dynamics of Thrombosis in Transcatheter Aortic Valves Jung Hee Seo, Chi Zhu, Zhongwang Dou, Jon Resar, Rajat Mittal Transcatheter aortic valve replacement (TAVR) with bioprosthetic valves (BPV) has become highly prevalent in recent years. While one advantage of BPVs over mechanical ones is the lower incidence of valve thrombosis, recent clinical studies have suggested a higher than expected incidence of subclinical bioprosthetic valve thrombosis (BVT). Many factors that might affect the transvalvular hemodynamics including the valve position, orientation, stent, and interaction with the coronary flow, have been suggested, but the casual mechanisms of valve thrombosis are still unknown. In the present study, the hemodynamics associated with the formation of BVT is investigated using a novel, coupled flow-structure-biochemical computational modeling. A reduced degree of freedom, fluid-structure-interaction model is proposed for the efficient simulation of the hemodynamics and leaflet dynamics in the BPVs. Simple models to take into account the effects of the stent and coronary flows have also been developed. Simulations are performed for canonical models of BPVs in the aorta in various configurations and the results are examined to provide insights into the mechanisms for valve thrombosis. [Preview Abstract] |
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KP1.00038: Cross-stream distribution of red blood cells in sickle-cell disease Xiao Zhang, Wilbur Lam, Michael Graham Experiments revealed that in blood flow, red blood cells (RBCs) tend to migrate away from the vessel walls, leaving a cell-free layer near the walls, while leukocytes and platelets tend to marginate towards the vessel walls. This segregation behavior of different cellular components in blood flow can be driven by their differences in stiffness and shape. An alteration of this segregation behavior may explain endothelial dysfunction and pain crisis associated with sickle-cell disease (SCD). It is hypothesized that the sickle RBCs, which are considerably stiffer than the healthy RBCs, may marginate towards the vessel walls and exert repeated damage to the endothelial cells. Direct simulations are performed to study the flowing suspensions of deformable biconcave discoids and stiff sickles representing healthy and sickle cells, respectively. It is observed that the sickles exhibit a strong margination towards the walls. The biconcave discoids in flowing suspensions undergo a so-called tank-treading motion, while the sickles behave as rigid bodies and undergo a tumbling motion. The margination behavior and tumbling motion of the sickles may help substantiate the aforementioned hypothesis of the mechanism for the SCD complications and shed some light on the design of novel therapies. [Preview Abstract] |
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KP1.00039: Hydrodynamics of Low Reynolds Respiratory-type Flows Erin Connor, Aaron True, John Crimaldi Both aquatic and terrestrial animals inhale surrounding fluid for metabolic and sensory purposes. As organisms inhale and exhale, complex fluid interactions occur both internal and external to the physiological orifice. Using both numerical and experimental approaches, we model an idealized respiratory flow consisting of cyclic inhalation and exhalation through a single cylindrical tube. We investigate the effect of varying Reynolds number (Re) as well as the ratio of the inhalation time to the exhalation time (I:E ratio) for a fixed inhalation volume. The numerical model is used for laminar cases at lower Re, whereas the experimental model permits the study to be extended into higher Reynolds numbers that include transitions to turbulence. We map the spatial distribution of both inhaled and exhaled fluid volumes. By comparing these two maps, we can compute the volume of exhaled fluid that is reingested during the subsequent inhalation. The models of interacting inhalation and exhalation exhibit a rich range of flow behaviors across Re number and I:E ratio. This study builds a foundation for more complex studies of animal respiration that will include more realistic morphologies. [Preview Abstract] |
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KP1.00040: Roughness Effects on the Formation of a Leading Edge Vortex Cassidy Elliott, Amy Lang, Redha Wahidi, Jacob Wilroy Microscopic scales cover the wings of Monarch butterflies, creating a patterned surface that acts as a natural energy capture mechanism. This patterning is thought to delay the growth of the leading edge vortex (LEV) produced by the flapping motion of a wing. Increased skin friction caused by the scales leads to a weaker LEV being shed into the butterfly's wake, lessening drag and increasing flight efficiency. To test how this roughness effects LEV formation, a plate of random roughness was designed in SolidWorks and printed on the Objet 30 Pro 3D printer. A 2x3x5 cubic foot tow tank was used to test the rough plate at Reynold's numbers of 1500, 3000, and 6000 (velocities of 8, 16, and 32 mm/s) at an angle of attack of 45 degrees. Images were captured of the LEV generated when the plate was towed upwards through the particle-seeded flow. These images were used to determine the XY velocity of the particles using a technique called Digital Particle Image Velocimetry (DPIV). Codes written in MATLAB were used to track and measure the strength of the LEV. Circulation values for the randomly-rough plate were then compared to the same values generated in a previous experiment that used a smooth plate and a grooved plate to determine the effect of the patterning on vortex development. [Preview Abstract] |
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KP1.00041: Flow Behavior Around a Fast-Starting Robotic Fish Ganzhong Ma, Todd Currier, Yahya Modarres-Sadeghi A robotic fish is used to study the flow behavior around the body of a fast-starting fish as it experiences a fast-start. The robotic fish is designed and built emulating a Northern Pike, Esox Lucius, which can accelerate at up to 245 m/s$^{\mathrm{2}}$. In previous studies, we had focused on the flow around the tail during the fast-start, by using a tail which acted flexibly in the preparatory stage and rigidly in the propulsive stage. We have extended that study by including the fish body in the experimental setup, where the body can bend into a C-shape, so that the influence of the body motion on the resulting flow around the structure can be understood as well. In the tests, the fish can rotate about a vertical axis, where a multi-axis force sensor measures flow forces acting on the body. Synchronized with the force measurement, flow visualizations using bubble image velocimetry are conducted, and the observed shed vortices are related to the peak forces observed during the maneuver. [Preview Abstract] |
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KP1.00042: Effects of Viscosity on the Performance of Air-Powered Liquid Jet Injectors Rocco Portaro, Hadi Jaber, Hoi Dick Ng Drug delivery without the use of hypodermic needles has been a long-term objective within the medical field. This study focuses on observing the effects of drug viscosity on injector performance for air-powered liquid jet injectors, as well as the viability of using this technology for delivering viscous-type medications such as monoclonal antibodies. The experiments are conducted through the use of a prototype injector which allows key parameters such as driver pressure, injection volume and nozzle size to be varied. Different viscosities which range from 0.9 cP to 87 cP are obtained by using a water-glycerol mix. The liquid jets emanating from the injector are assessed using high speed photography as well as a pressure transducer. Experimental findings are then compared to a CFD model which considered experimental geometry and parameters. The results of this study highlight the effect of viscosity on the operating pressure of the injector and the reduction in jet stagnation pressure. It also illustrates improved jet confinement as viscosity is increased, a finding which is in line with the numerical model, and should play a key role in improving the device's characteristics for puncturing skin. [Preview Abstract] |
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KP1.00043: Binary gas mixture in a high speed channel Dr. Sahadev Pradhan The viscous, compressible flow in a 2D wall-bounded channel, with bottom wall moving in the positive $x-$ direction, simulated using the direct simulation Monte Carlo (DSMC) method, has been used as a test bed for examining different aspects of flow phenomenon and separation performance of a binary gas mixture at Mach number \textit{Ma }$=$\textit{ (U\textunderscore w / }$\backslash $\textit{sqrt(}$\gamma $\textit{ k\textunderscore B T\textunderscore w /m) }in the range\textit{ 0.1 \textless Ma \textless 30}, and Knudsen number \textit{Kn }$=$\textit{ 1/(}$\backslash $\textit{sqrt(2) }$\pi $\textit{ d\textasciicircum 2 n\textunderscore d H)} in the range \textit{0.1 \textless Kn \textless 10}. The generalized analytical model is formulated which includes the fifth order differential equation for the boundary layer at the channel wall in terms of master potential ($\chi )$, which is derived from the equations of motion in a 2D rectangular $(x - y)$ coordinate. The starting point of the analytical model is the Navier-Stokes, mass, momentum and energy conservation equations in the $(x - y)$ coordinate, where $x$ and $y$ are the streamwise and wall-normal directions, respectively. The linearization approximation is used ((Pradhan {\&} Kumaran\textit{, J. Fluid Mech -}2011); (Kumaran {\&} Pradhan, \textit{J. Fluid Mech -}2014)), where the equations of motion are truncated at linear order in the velocity and pressure perturbations to the base flow, which is an isothermal compressible Couette flow. Additional assumptions in the analytical model include high aspect ratio \textit{(L \textgreater \textgreater H)}, constant temperature in the base state (isothermal condition), and low Reynolds number (laminar flow). The analytical solutions are compared with direct simulation Monte Carlo (DSMC) simulations and found good agreement (with a difference of less than 10{\%}), provided the boundary conditions are accurately incorporated in the analytical solution. [Preview Abstract] |
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KP1.00044: Dissolution of methane bubbles with hydrate armoring in deep ocean conditions Margarita Kovalchuk, Scott Socolofsky The deep ocean is a storehouse of natural gas. Methane bubble moving upwards from marine sediments may become trapped in gas hydrates. It is uncertain precisely how hydrate armoring affects dissolution, or mass transfer from the bubble to the surrounding water column. The Texas A\&M Oilspill Calculator was used to simulate a series of gas bubble dissolution experiments conducted in the United States Department of Energy National Energy Technology Laboratory High Pressure Water Tunnel. Several variations of the mass transfer coefficient were calculated based on gas or hydrate phase solubility and clean or dirty bubble correlations. Results suggest the mass transfer coefficient may be most closely modeled with gas phase solubility and dirty bubble correlation equations. Further investigation of hydrate bubble dissolution behavior will refine current numeric models which aid in understanding gas flux to the atmosphere and plumes such as oil spills. [Preview Abstract] |
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KP1.00045: The growth of oscillating bubbles in an ultrasound field Risa Yamauchi, Tatsuya Yamashita, Keita Ando From our recent experiments to test particle removal by underwater ultrasound, dissolved gas supersaturation is found to play an important role in physical cleaning; cavitation bubble nucleation can be triggered easily by weak ultrasound under the supersaturation and mild motion of the bubbles contributes to efficient cleaning without erosion. The state of gas bubble nuclei in water is critical to the determination of a cavitation inception threshold. Under ultrasound forcing, the size of bubble nuclei is varied by the transfer of dissolved gas (i.e., rectified diffusion); the growth rate will be promoted by the supersaturation and is thus expected to contribute to cavitation activity enhancement. In the present work, we experimentally study rectified diffusion for bubbles attached at glass surfaces in an ultrasound field. We will present the evolution of bubble nuclei sizes with varying parameters such as dissolved oxygen supersaturation, and ultrasound intensity and frequency. [Preview Abstract] |
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KP1.00046: Experiment and analysis of shock waves radiated from pulse laser focusing in a gelatin gel Nobuyuki Nakamura, Keita Ando A fundamental understanding of shock and bubble dynamics in human tissues is essential to laser application for medical purposes. Here, we experimentally study the dynamics of shock waves in viscoelastic media. A nanosecond laser pulse of wavelength at 532 nm and of energy up to 2.66 ± 0.09 mJ was focused through a microscope objective lens (10 x, NA = 0.30) into a gel of gelatin concentration at 3 and 10 wt\%; a shock wave and a bubble can be generated, respectively, by rapid expansion of the laser-induced plasma and local heat deposition after the plasma recombines. The shock propagation and the bubble growth were recorded by a ultra-high-speed camera at 100 Mfps. The shock evolution was determined by image analysis of the recording and the shock pressure in the near field was computed according to the Rankine-Hugoniot relation. The far-field pressure was measured by a hydrophone. In the poster, we will present the decay rate of the shock pressure in the near and far fields and examine viscous effects on the shock dynamics. [Preview Abstract] |
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KP1.00047: Ultrasound-induced oscillations of gas bubbles in contact with gelatin gel surfaces Sosuke Fukui, Keita Ando Ultrasound-induced dynamics of gas bubbles in the vicinity of deformable boundaries are studied experimentally, as a simplified model of sonoporation in medicine. In our experiment, 28-kHz underwater ultrasound was irradiated to a gas bubble nuclei (of radius from 60 $\mu$m to 200 $\mu$m) sitting at gel surfaces (of gelatin concentration from 6 wt\% to 16 wt\%) and the bubble dynamics were recorded by a high-speed camera. The repeated deformation of the gel surface was found to be in phase with volumetric oscillation of the bubble. A liquid jet, which can appear toward the collapse phase in the bubble oscillation in volume, produced localized surface deformation, which is an important observation in the context of sonoporation. We characterize the maximum displacement of the gel surface with varying the bubble nuclei radius (in comparison to the resonant radius fixed approximately at 117 $\mu$m). We also examine the phase difference between the ultrasound and the bubble dynamics under the influence of the deformable boundary. [Preview Abstract] |
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KP1.00048: Design of Counter Flow Burner for Oxy-Combustion Studies Using CFD Laura Holifield, Mruthunjaya Uddi Flat flames are useful for studying the fundamental physics of combustion through laser diagnostics and comparison with commercially (or open source) available 1D software such as Chemkin or Cantera. A counter flow burner is capable of producing this flat flame by achieving a flat velocity profile along the outlet. However, what is necessary to achieve this is not readily available. In order to find the optimal design parameters for a counter flow burner, different geometries and velocities were tested at the University of Alabama using Ansys Fluent CFD software. The geometry was axisymmetric and oriented horizontally on the xy-plane. The design of this burner was aimed at reducing the boundary layer while keeping the radial velocity at a minimum. The objective of this paper is to examine the effects of varying the angle, nozzle length, filet radius, inlet to outlet ratio, and velocity on the boundary layer and radial velocity of a counter flow burner. [Preview Abstract] |
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KP1.00049: Potential Flow Model for Compressible Stratified Rayleigh-Taylor Instability Grant Rydquist, Scott Reckinger, Mark Owkes, Scott Wieland The Rayleigh-Taylor Instability (RTI) is an instability that occurs when a heavy fluid lies on top of a lighter fluid in a gravitational field, or a gravity-like acceleration. It occurs in many fluid flows of a highly compressive nature. In this study potential flow analysis (PFA) is used to model the early stages of RTI growth for compressible fluids. In the localized region near the bubble tip, the effects of vorticity are negligible, so PFA is applicable, as opposed to later stages where the induced velocity due to vortices generated from the growth of the instability dominate the flow. The incompressible PFA is extended for compressibility effects by applying the growth rate and the associated perturbation spatial decay from compressible linear stability theory. The PFA model predicts theoretical values for a bubble terminal velocity for single-mode compressible RTI, dependent upon the Atwood (A) and Mach (M) numbers, which is a parameter that measures both the strength of the stratification and intrinsic compressibility. The theoretical bubble terminal velocities are compared against numerical simulations. The PFA model correctly predicts the M dependence at high A, but the model must be further extended to include additional physics to capture the behavior at low A. [Preview Abstract] |
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KP1.00050: Semi-Extrapolated Finite Difference Schemes and Their Stability Andrew Brandon, Brendan Drachler, Carter Alexander When solving partial differential equations, finite difference (FD) methods are a popular choice. Several factors come into play when choosing a FD method, such as stability and cost of computation. Implicit methods have large stability regions, while explicit methods typically have small regions. Yet implicit methods are expensive to use, while explicit methods are inexpensive. In response to the small stability regions of explicit methods and the cost of implicit methods, we developed a novel discretization technique that generates explicit schemes by uniquely applying extrapolation to implicit schemes. The use of extrapolation can severely curtail a scheme`s stability, however, our technique results in explicit schemes that exhibit extended stability regions compared to those of analogous explicit schemes, without a loss in accuracy. In our presentation, we`ll review the stability regions of several popular spatially centered FD schemes. We`ll then discuss our technique and how it can be used to solve the advection-diffusion equation. Upon discretizing this benchmark equation according to our technique, we`ll analyze the stability regions of the resulting schemes and demonstrate nontrivial improvements in stability as compared to the stability of analogous explicit methods. [Preview Abstract] |
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KP1.00051: Resolving collisions in Stokes suspensions with an efficient and stable potential-free constrained optimization algorithm Wen Yan, Eduardo Corona, Shravan Veerapaneni, Michael Shelley A common challenge in simulating dense suspension of rigid particles in Stokes flow is the numerical instability that arises due to particle collisions. To overcome this problem, often a strong repulsive potential between particles is prescribed. This in turn leads to numerical stiffness and dramatic reduction in stable time-step sizes. In this work, we eliminate such stiffness by introducing contact constraints explicitly and solving the hydrodynamic equations in tandem with a linear complementarity problem with inequality constraints. The Newton's third law of the collision force is explicitly guaranteed to allow consistent calculation of collision stresses. Efficient parallelization for shared-memory and distributed-memory architectures is also implemented. This method can be coupled to any Stokes hydrodynamics solver for particles with various shapes and allows us to simulate $10^4 \sim 10^7$ spheres on a laptop, depending on the cost of the Stokes hydrodynamics solver. We demonstrate its performance on a range of applications from active matter to multi-physics problems. [Preview Abstract] |
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KP1.00052: ABSTRACT WITHDRAWN |
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KP1.00053: 2D CFD Airfoil Analysis Grace Babb This work aims to produce a higher fidelity model of the blades for NASA's X-57 all electric propeller driven experimental aircraft. This model will, in turn, allow for more accurate calculations of the thrust each propeller can generate. This work uses computational fluid dynamics (CFD) to first analyze the propeller blades as a series of 11 differently shaped airfoils and calculate, among other things, the coefficients for lift and drag associated with each airfoil at different angles of attack. OpenFOAM---a C$++$ library that can be used to create series of applications for pre-processing, solving, and post-processing---is one of the primary tools utilized in these calculations. By comparing the data OpenFOAM generates about the NACA 23012 airfoil with existing experimental data about the NACA 23012 airfoil, the reliability of our model is measured and verified. A trustworthy model can then be used to generate more data and sent to NASA to aid in the design of the actual aircraft. [Preview Abstract] |
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KP1.00054: Validating computational predictions of night-time ventilation in Stanford's Y2E2 building Chen Chen, Giacomo Lamberti, Catherine Gorle Natural ventilation can significantly reduce building energy consumption, but robust design is a challenging task. We previously presented predictions of natural ventilation performance in Stanford's Y2E2 building using two models with different levels of fidelity, embedded in an uncertainty quantification framework to identify the dominant uncertain parameters and predict quantified confidence intervals. The results showed a slightly high cooling rate for the volume-averaged temperature, and the initial thermal mass temperature and window discharge coefficients were found to have an important influence on the results. To further investigate the potential role of these parameters on the observed discrepancies, the current study is performing additional measurements in the Y2E2 building. Wall temperatures are recorded throughout the nightflush using thermocouples; flow rates through windows are measured using hotwires; and spatial variability in the air temperature is explored. The measured wall temperatures are found the be within the range of our model assumptions, and the measured velocities agree reasonably well with our CFD predications. Considerable local variations in the indoor air temperature have been recorded, largely explaining the discrepancies in our earlier validation study. Future work will therefore focus on a local validation of the CFD results with the measurements.~ [Preview Abstract] |
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KP1.00055: CFD Simulations to Improve Ventilation in Low-Income Housing Rosemond Ho, Catherine Gorle Quality of housing plays an important role in public health. In Dhaka, Bangladesh, the leading causes of death include tuberculosis, lower respiratory infections, and chronic obstructive pulmonary disease, so improving home ventilation could potentially mitigate these negative health effects. The goal of this project is to use computational fluid dynamics (CFD) to predict the relative effectiveness of different ventilation strategies for Dhaka homes. A Reynolds-averaged Navier-Stokes CFD model of a standard Dhaka home with apertures of different sizes and locations was developed to predict air exchange rates. Our initial focus is on simulating ventilation driven by buoyancy-alone conditions, which is often considered the limiting case in natural ventilation design. We explore the relationship between ventilation rate and aperture area to determine the most promising configurations for optimal ventilation solutions. Future research will include the modeling of wind-driven conditions, and extensive uncertainty quantification studies to investigate the effect of variability in the layout of homes and neighborhoods, and in local wind and temperature conditions. The ultimate objective is to formulate robust design recommendations that can reduce risks of respiratory illness in low-income housing. [Preview Abstract] |
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KP1.00056: The F-UNCLE Project: Functional UNcertainty Constrained by Law and Experiment Andrew Fraser We are fitting equations of state (EOS) to the mixtures of gasses produced by detonating explosives. Given a set of experimental measurements, we intend our code to provide: 1. An estimate of the EOS; 2. A characterization the residual uncertainty. 3. A description of how each different experiment (both those that have been run and those that are proposed) constrains the estimated EOS. Matrices called the Fisher Information represent the constraints. The presentation will outline the problem and illustrate the resulting constraints. [Preview Abstract] |
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KP1.00057: Effect of internal flow and evaporation on hydrogel assembly process at droplet interface. Giho Kang, Baekhoon Seong, Yeonghyeon Gim, Han Seo Ko, Doyoung Byun Recently, controlling the behavior of nanoparticles inside liquid droplet has been widely studied. There have been many reports about the mechanism of the nanoparticles assembly and fabrication of a thin film on a substrate. However, the assembly mechanism at a liquid-air interface has not been clearly understood to form polymer chains into films. Herein, we investigated the role of internal flow on the thin film assembly process at the interface of the hydrogel droplet. The internal fluid flow during the formation of the hydrogel film was visualized systematically using micro-PIV (Particle image velocimetry) technique at various temperatures. We show that the buoyancy effect and convection flow induced by heat can affect the film morphology and its mechanical characteristics. Due to the accelerated fluid flow inside the droplet and evaporation flux, densely assembled hydrogel film was able to be formed. Film strength was increased 24{\%} with temperature increase from 40 to 80 degrees Celsius. We expect our investigations could be applied to many applications such as self-assembly of planar structures at the interface in coating and printing process. [Preview Abstract] |
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KP1.00058: Quantifying the role of noise on droplet decisions in bifurcating microchannels Masoud Norouzi Darabad, Mark Vaughn, Siva Vanapalli While many aspects of path selection of droplets flowing through a bifurcating microchannel have been studied, there are still unaddressed issues in predicting and controlling droplet traffic. One of the more important is understanding origin of aperiodic patterns. As a new tool to investigate this phenomena we propose monitoring the continuous time response of pressure fluctuations at different locations. Then we use time-series analysis to investigate the dynamics of the system. We suggest that natural system noise is the cause of irregularity in the traffic patterns. Using a mathematical model, we investigate the effect of noise on droplet decisions at the junction. Noise can be derived from different sources including droplet size variation, droplet spacing, and pump induced velocity fluctuation. By analyzing different situations we explain system behavior. We also investigate the ``memory'' of a microfluidic system in terms of the resistance to perturbations that quantify the allowable deviation in operating condition before the system changes state. [Preview Abstract] |
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KP1.00059: Scattering of liquid droplets from axisymmetric targets Jacob Hale, Jacob Boudreau Droplets that glide along a bath of the same fluid are seen to scatter from a cylindrical meniscus analogous to Coulomb scattering of like-charged atomic particles. We define the impact parameter, $b$, as the distance between the tangent line to the initial trajectory of the droplet and the parallel radial line from the center of target. The scattering angle, $\theta$, and the distance of closest approach, $r_{\rm c}$ are measured as functions of $b$. The asymptotic behavior of these values presents as expected for a rapidly decaying potential between the droplet and the target. [Preview Abstract] |
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KP1.00060: Dynamics of a surfactant-covered viscous drop under an electric field: Effects of surfactant diffusivity Herve Nganguia, On Shun Pak, Yuan-nan Young Electrohydrodynamics of a viscous drop covered with surfactants is highly relevant in many industrial applications. Previously we have used a leaky dielectric model to investigate the deformation of a spheroidal viscous drop covered with non-diffusive surfactants (\textbf{Phys. Fluids}, 25, 092106, 2013). In this work we extended the previous spheroidal model to both dielectric and conducting drop covered with diffusive surfactants. We propose spheroidal models of leaky and conducting drops in electric field for both small and intermediate deformations. We further couple the models to surfactant dynamics, and investigate the effects of varying surfactant concentrations and P\'{e}clet numbers on deformation. We conclude with a discussion and extensions to the process of electro-coalescence. [Preview Abstract] |
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KP1.00061: Temperature distribution of a water droplet moving on a heated super-hydrophobic surface under the icing condition Masafumi Yamazaki, Yutaka Sumino, Katsuaki Morita In the aviation industry, ice accretion on the airfoil has been a hazardous issue since it greatly declines the aerodynamic performance. Electric heaters and bleed air, which utilizes a part of gas emissions from engines, are used to prevent the icing. Nowadays, a new de-icing system combining electric heaters and super hydrophobic coatings have been developed to reduce the energy consumption. In the system, the heating temperature and the coating area need to be adjusted. Otherwise, the heater excessively consumes energy when it is set too high and when the coating area is not properly located, water droplets which are once dissolved possibly adhere again to the rear part of the airfoil as runback ice In order to deal with these problems, the physical phenomena of water droplets on the hydrophobic surface demand to be figured out. However, not many investigations focused on the behavior of droplets under the icing condition have been conducted. In this research, the temperature profiling of the rolling droplet on a heated super-hydrophobic surface is experimentally observed by the dual luminescent imaging. [Preview Abstract] |
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KP1.00062: Droplet formation at the non-equilibrium water/water (w/w) interface Youchuang Chao, Sze Yi Mak, Tiantian Kong, Zijing Ding, Ho Cheung Shum The interfacial instability at liquid-liquid interfaces has been intensively studied in recent years due to their important role in nature and technology. Among them, two classic instabilities are Rayleigh-Taylor (RT) and double diffusive (DD) instabilities, which are practically relevant to many industrial processes, such as geologic CO2 sequestration. Most experimental and theoretical works have focused on RT or DD instability in binary systems. However, the study of such instability in complex systems, such as non-equilibrium ternary systems that involves mass-transfer-induced phase separation, has received less attention. Here, by using a ternary system known as the aqueous two-phase system (ATPS), we investigate experimentally the behavior of non-equilibrium water/water (w/w) interfaces in a vertically orientated Hele-Shaw cell. We observe that an array of fingers emerge at the w/w interface, and then break into droplets. We explore the instability using different concentrations of two aqueous phases. Our experimental findings are expected to inspire the mass production of all-aqueous emulsions in a simple setup. [Preview Abstract] |
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KP1.00063: Assembly of silver nanowire ring induced by liquid droplet Baekhoon Seong, Hyun Sung Park, Ilkyeong Chae, Hyungdong Lee, Xiaofeng Wang, Hyung-Seok Jang, Jaehyuck Jung, Changgu Lee, Liwei Lin, Doyoung Byun Several forces in the liquid droplet drive the nanomaterials to naturally form an assembled structure. During evaporation of a liquid droplet, nanomaterials can move to the rim of the droplet by convective flow and capillary flow, due to the difference in temperature between the top and contact line of the droplet. Here, we demonstrate a new, simple and scalable technology for the fabrication of ring-shaped Ag NWs by a spraying method. We experimentally identify the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. We investigated the progress of ring shape formation of Ag NWs according to the droplet size with theoretically calculated optimal conditions. As such, this self-assembly technique of making ring-shaped structures from Ag NWs could be applied to other nanomaterials. [Preview Abstract] |
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KP1.00064: Motion of Droplets on Superhydrophobic Surfaces Alexander Smith, Shaun Hendy, Keoni Mahelona, Rebecca Sutton While the rolling motion of droplets on superhydrophobic (SHP) surfaces with conventional slip lengths has been investigated and observed experimentally, the existence of slip-dominated regimes on surfaces with high slip-lengths remains relatively unexplored. In this paper, we investigate the roles of droplet size and surface geometry on the average velocity of droplets travelling down SHP surfaces with molecular dynamics simulations, and compare with an extension of prior models of droplet motion on SHP surfaces, which assumes an effective slip condition at the SHP surface. This approach yields three limiting cases where the droplet velocity is dominated by viscous dissipation, surface friction or contact line friction respectively. We find a distinct size regime where the motion of small droplets is determined by frictional dissipation at the fluid-surface interface and the droplet velocity is proportional to the droplet radius. As droplet size increases beyond a slip-dependent threshold, we see the usual rolling state where droplet motion is dominated by viscous dissipation and the speed is inversely proportional to droplet radius. We also simulate the movement of droplets across a surface with a moving wettability gradient, and show that there exists a maximum velocity above which the droplet cannot keep up with the moving field. [Preview Abstract] |
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KP1.00065: Spreading of a droplet accompanying with an interaction with a spherical particle settled on a smooth substrate Tetsuya Ogawa, Lizhong Mu, Toshihiro Kaneko, Harunori N. Yoshikawa, Farzam Zoueshtiagh, Ichiro Ueno Objective of this study is to elucidate experimentally the phenomenon that the macroscopic contact line (M-CL) of a droplet spreading on a horizontal substrate accelerates due to interaction with a spherical particle. We observed the temporal variation of the M-CL rising on the spherical particle and the liquid film profile near the contact line around the particle under low capillary number condition. It was found that the particle still remains settled on the substrate even after the interaction with the front edge of the droplet under smaller capillary number in the present condition. The particle is sucked toward the bulk of the droplet by the interaction with the droplet under moderate capillary number condition. We will discuss the condition of the M-CL acceleration from the shape of the meniscus. [Preview Abstract] |
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KP1.00066: A Molecular Dynamics Study on Selective Cation Depletion from an Ionic Liquid Droplet under an Electric Field Yudong Yang, Myungmo Ahn, Dojin Im, Jungmin Oh, Inseok Kang General electrohydrodynamic behavior of ionic liquid droplets under an electric field is investigated using MD simulations. Especially, a unique behavior of ion depletion of an ionic liquid droplet under a uniform electric field is studied. Shape deformation due to electric stress and ion distributions inside the droplet are calculated to understand the ionic motion of imidazolium-based ionic liquid droplets with 200 ion pairs of 2 kinds of ionic liquids: EMIM-NTf2 and EMIM-ES. The intermolecular force between cations and anions can be significantly different due to the nature of the structure and charge distribution of the ions. Together with an analytical interpretation of the conducting droplet in an electric field, the MD simulation successfully explains the mechanism of selective ion depletion of an ionic liquid droplet in an electric field. The selective ion depletion phenomenon has been adopted to explain the experimentally observed retreating motion of a droplet in a uniform electric field. The effect of anions on the cation depletion phenomenon can be accounted for from a direct approach to the intermolecular interaction. [Preview Abstract] |
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KP1.00067: Designing high speed diagnostics Gerardo Veliz Carrillo, Adam Martinez, Swathi Mula, Kathy Prestridge Timing and firing for shock-driven flows is complex because of jitter in the shock tube mechanical drivers. Consequently, experiments require dynamic triggering of diagnostics from pressure transducers. We explain the design process and criteria for setting up re-shock experiments at the Los Alamos Vertical Shock Tube facility, and the requirements for particle image velocimetry and planar laser induced fluorescence measurements necessary for calculating Richtmeyer-Meshkov variable density turbulent statistics. Dynamic triggering of diagnostics allows for further investigation of the development of the Richtemeyer-Meshkov instability at both initial shock and re-shock. [Preview Abstract] |
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KP1.00068: Effect of Propeller Angle Relative to Flow on Aerodynamic Characteristics. Joseph Schueller, Paul Hubner As the interest in small unmanned air systems (UASs) for delivery and surveillance grows, new hybrid designs are being studied to take advantage of both quadcopters and fixed-wing aircraft. The tiltrotor design is able to combine the vertical take-off, hover, and landing of a multi-rotor copter with the efficiency of forward flight of a conventional airplane. However, literature documenting aerodynamic performance of the rotor as it rotates between the forward-flight and hover positions, especially in this low Reynolds number range, is limited. This data is critical for validating computational models and developing safe transition corridors. The objective of this research was to design, build and test a rotor thrust stand capable of rotating between the forward-flight and hover configurations suitable for senior design studies at low Reynolds number research. The poster covers the design of the rotating mechanism, the range and resolution of the load cell, and the thrust, torque and efficiency results for a conventional UAS motor and propeller for various advance ratios and thrust-line orientations. [Preview Abstract] |
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KP1.00069: Three-dimensional laser-induced fluorescence measurements of turbulent chemical plumes Aaron True, John Crimaldi In order to find prey, mates, and suitable habitat, many organisms must navigate through complex chemical plume structures in turbulent flow environments. In this context, we investigate the spatial and temporal structure of chemical plumes released isokinetically into fractal-grid-generated turbulence in an open channel flow. We first utilized particle image velocimetry (PIV) to characterize flow conditions (mean free stream velocities, turbulence intensities, turbulent kinetic energy dissipation rates, Taylor Reynolds numbers). We then implemented a newly developed high-resolution, high-speed, volumetric scanning laser-induced fluorescence (LIF) system for near time-resolved measurements of three-dimensional chemical plume structures. We investigated cases with and without a cylinder wake, and compare statistical (mean, variance, intermittency, probability density functions) and spectral (power spectrum of concentration fluctuations) characteristics of the chemical plume structure. Stretching and folding of complex three-dimensional filament structures during chaotic turbulent mixing is greatly enhanced in the cylinder wake case. In future experiments, we will implement simultaneous PIV and LIF, enabling computation of the covariance of the velocity and chemical concentration fluctuations and thus estimation of turbulent eddy diffusivities. [Preview Abstract] |
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KP1.00070: Experimental study on spatio-temporal behavior of a single particle forming a particle accumulation structure (PAS) in half-zone liquid bridge Takeru Oba, Ichiro Ueno, Toshihiro Kaneko We focus on particle behavior due to thermocapillary-driven convection in a half-zone liquid bridge of high-Prandtl number fluid. It has been known that the suspended particles exhibit a unique solid-like structure known as 'particle accumulation structure (PAS)' in a rotating frame of reference with traveling-type hydrothermal wave. It is said that PAS is caused by interaction between particles and the free surface of a half-zone liquid bridge. Such structures arise even under small Stokes number conditions. When observing PAS two-dimensionally, it looks like a closed single string, but the actual movement of particles is different. Therefore we employ three-dimensional particle tracking velocimetry to the half-zone liquid bridge of 2.5 mm in radius and 1.7 mm in height, and detect the particle behaviors close to the free surface. We explain the spatio-temporal correlation between the solid-like global structure of PAS and the local particle motions, and make comparisons with proposed physical models of PAS formation. [Preview Abstract] |
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KP1.00071: Unstable bidimensional grids of liquid filaments: Drop pattern after breakups Javier Diez, Ingrith Cuellar, Pablo Ravazzoli, Alejandro Gonzalez A rectangular grid formed by liquid filaments on a partially wetting substrate evolves in a series of breakups leading to arrays of drops with different shapes distributed in a rather regular bidimensional pattern. Our study is focused on the configuration produced when two long parallel filaments of silicone oil, which are placed upon a glass substrate previously coated with a fluorinated solution, are crossed perpendicularly by another pair of long parallel filaments. A remarkable feature of this kind of grids is that there are two qualitatively different types of drops. While one set is formed at the crossing points, the rest are consequence of the breakup of shorter filaments formed between the crossings. Here, we analyze the main geometric features of all types of drops, such as shape of the footprint and contact angle distribution along the drop periphery. The formation of a series of short filaments with similar geometric and physical properties allows us to have simultaneously quasi identical experiments to study the subsequent breakups. We develop a simple hydrodynamic model to predict the number of drops that results from a filament of given initial length and width.This model is able to yield the length intervals corresponding to a small number of drops. [Preview Abstract] |
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KP1.00072: Effects of Initial Conditions on Shock Driven Flows. Adam A. Martinez, Swathi M. Mula, John Charonko, Kathy Prestridge The spatial and temporal evolution of shock-driven, variable density flows, such as the Richtmyer Meshkov (RM) instability, are strongly influenced by the initial conditions (IC's) of the flow at the time of interaction with shockwave. We study the effects of the IC's on the Vertical Shock Tube (VST) and on flows from Mach $=$1.2 to Mach$=$9. Experiments at the VST are of an Air-SF6 (At$=$0.6) multimode interface. Perturbations are generated using a shear layer with a flapper plate. Planar Laser Induced Fluorescence (PLIF) is used to characterize the IC's. New experiments are occurring using the Powder Gun driver at LANL Proton Radiography (pRad) facility. Mach number up to M$=$9 accelerate a Xenon-Helium (At$=$0.94) interface that is perturbed using a membrane supported by different sized grids. This presentation focuses on how to design and characterize different types of initial conditions for experiments. [Preview Abstract] |
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KP1.00073: A Twist on the Richtmyer-Meshkov Instability Bertrand Rollin, Rahul Koneru, Frederick Ouellet The Richtmyer-Meshkov instability is caused by the interaction of a shock wave with a perturbed interface between two fluids of different densities. Typical contexts in which it plays a key role include inertial confinement fusion, supernovae or scramjets. However, little is known of the phenomenology of this instability if one of the interacting media is a dense solid-particle phase. In the context of an explosive dispersal of particles, this gas-particle variant of the Richtmyer-Meshkov instability may play a role in the late time formation of aerodynamically stable particle jets. Thus, this numerical experiment aims at shedding some light on this phenomenon with the help of high fidelity numerical simulations. Using a Eulerian-Lagrangian approach, we track trajectories of computational particles composing an initially corrugated solid particle curtain, in a two-dimensional planar geometry. This study explores the effects of the initial shape (designed using single mode and multimode perturbations) and volume fraction of the particle curtain on its subsequent evolution. Complexities associated with compaction of the curtain of particles to the random close packing limit are avoided by constraining simulations to modest initial volume fraction of particles. [Preview Abstract] |
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KP1.00074: Visualization of the flow in a cylindrical container with a rotating disk Ryoki Imahoko, Hiroki Kurakata, Jun Sakakibara We studied a behavior of the flow in a cylindrical container with a rotating disk. The apparatus consists of a fixed cylindrical container of the inner diameter of 140 mm and height H, and a coaxial rotating disc with a diameter of 140 mm connected with a cylindrical shaft driven by an electrical motor. The radial gap between rotating disk and side wall is very slight distance. The height H is variable up to 100 mm. The velocity distribution in the container was measured by means of particle image velocimetry (PIV). The results of this experiments will be discussed at the conference. [Preview Abstract] |
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KP1.00075: Measurement of flow inside a vacuum cleaner head Ryotaro Iguchi, Hisataka Ban, Jun Sakakibara Vacuum cleaner head with rotating brushes is widely used as a home appliance. Although it efficiently collects dusts from the floor, flow field of the air and motion of the dust inside the head have not been fully investigated. In this study, we performed 3D-PIV (particle tracking velocimetry) measurement of velocity field inside the head. Water was used as working fluid, which allows a use of fluorescent particle to reduce unwanted reflection from the brushes and inner surface of the head. Mean velocity field and turbulence statistics in the head with and without the brush will be presented. [Preview Abstract] |
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KP1.00076: Long-Time Asymptotics of a Box-Type Initial Condition in a Viscous Fluid Conduit Nevil Franco, Emily Webb, Michelle Maiden, Mark Hoefer, Gennady El The initial value problem for a localized hump disturbance is fundamental to dispersive nonlinear waves, beginning with studies of the celebrated, completely integrable Korteweg-de Vries equation. However, understanding responses to similar disturbances in many realistic dispersive wave systems is more complicated because they lack the mathematical property of complete integrability. This project applies Whitham nonlinear wave modulation theory to estimate how a viscous fluid conduit evolves this classic initial value problem. Comparisons between theory, numerical simulations, and experiments are presented. The conduit system consists of a viscous fluid column (glycerol) and a diluted, dyed version of the same fluid introduced to the column through a nozzle at the bottom. Steady injection and the buoyancy of the injected fluid leads to the eventual formation of a stable fluid conduit. Within this structure, a one hump disturbance is introduced and is observed to break up into a quantifiable number of solitons. This structure's experimental evolution is to Whitham theory and numerical simulations of a long-wave interfacial model equation. The method presented is general and can be applied to other dispersive nonlinear wave systems. [Preview Abstract] |
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KP1.00077: Laminar flow drag reduction on a soft porous media surface Zhenxing Wu, Michael Tambasco, Parisa Mirbod The ability to control flow reduction in microchannels could significantly advance microfluidic-based devices in a wide range of industrial applications including biomedical fields. The aim of this work is to understand the fundamental physics of the laminar skin friction coefficient and the related drag reduction due to the existence of porous media in the pressure-driven flow. We conducted an analytical framework to predict a laminar Newtonian fluid flow and corresponding drag reduction in a rectangular microchannel which coated with various soft random porous media. Specifically, we present predictions of the laminar skin friction coefficient, and drag reduction for pressure-driven flows. We found the laminar drag reduction is strongly depended on the Darcy permeability of porous medium, the thickness of the permeable layer, and the height of the microchannel. To verify the accuracy of our analytical predictions, several pressure-drop experiments were conducted. We chose various combinations of porous material and the morphology of the fibers to achieve a unique height ratio, between the height of two domains, and permeability parameter of porous media for each experiment. We found a good agreement between the experiments and analytical predictions of laminar drag reduction. [Preview Abstract] |
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KP1.00078: Model of an Evaporating Drop Experiment Nicolas Rodriguez A computational model of an experimental procedure to measure vapor distributions surrounding sessile drops is developed to evaluate the uncertainty in the experimental results. Methanol, which is expected to have predominantly diffusive vapor transport, is chosen as a validation test for our model. The experimental process first uses a Fourier transform infrared spectrometer to measure the absorbance along lines passing through the vapor cloud. Since the measurement contains some errors, our model allows adding random noises to the computational integrated absorbance to mimic this. Then the resulting data are interpolated before passing through a computed tomography routine to generate the vapor distribution. Next, the gradients of the vapor distribution are computed along a given control volume surrounding the drop so that the diffusive flux can be evaluated as the net rate of diffusion out of the control volume. Our model of methanol evaporation shows that the accumulated errors of the whole experimental procedure affect the diffusive fluxes at different control volumes and are sensitive to how the noisy data of integrated absorbance are interpolated. This indicates the importance of investigating a variety of data fitting methods to choose which is best to present the data. [Preview Abstract] |
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KP1.00079: Inertial objects in complex flows Rayhan Syed, George Ho, Samuel Cavas, Jialun Bao, Philip Yecko Chaotic Advection and Finite Time Lyapunov Exponents both describe stirring and transport in complex and time-dependent flows, but FTLE analysis has been largely limited to either purely kinematic flow models or high Reynolds number flow field data. The neglect of dynamic effects in FTLE and Lagrangian Coherent Structure studies has stymied detailed information about the role of pressure, Coriolis effects and object inertia. We present results of laboratory and numerical experiments on time-dependent and multi-gyre Stokes flows. In the lab, a time-dependent effectively two-dimensional low Re flow is used to distinguish transport properties of passive tracer from those of small paramagnetic spheres. Companion results of FTLE calculations for inertial particles in a time-dependent multi-gyre flow are presented, illustrating the critical roles of density, Stokes number and Coriolis forces on their transport. Results of Direct Numerical Simulations of fully resolved inertial objects (spheroids) immersed in a three dimensional (ABC) flow show the role of shape and finite size in inertial transport at small finite Re. [Preview Abstract] |
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KP1.00080: The stability of baroclinic diffusion-driven boundary layers in the abyssal ocean Bryan Kaiser, Lawrence Pratt The diffusion of adiabatic boundary conditions at sloping boundaries into stratified, diffusive flows produces baroclinic vorticity that drives laminar boundary layer (BL) flows. Many studies have investigated laminar solutions but observations of BLs in the abyssal ocean depict vigorous turbulence. The turbulent BLs generate upwelling and downwelling on long time scales and therefore may play an important role in the global overturning circulation and ultimately in the climate state. We investigate the stability of BLs in stratified, diffusive flows on sloping boundaries subjected to tidal oscillations and rotation for conditions typical of the extra-polar abyss on shallow slopes in order to gain insight into the structure of the observed turbulence. While linear stability analysis can predict the onset of instability in some flows (such as Rayleigh-B\'{e}nard and Taylor-Couette flows), it fails to predict the onset of instabilities due to shear forces (such as Poiseuille and Couette flow). Both shear instability and convective instability are possible in the BLs of interest, therefore we use a combined approach of linear stability analysis and simulation to determine stability criteria. We present the physical mechanisms of instability as well as the stability criteria. [Preview Abstract] |
(Author Not Attending)
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KP1.00081: Flow induced on a salt waterbody due to the impingement of a freshwater drop. Islam Benouaguef, Edison Amah, Naga Musunuri, Denis Blackmore, Ian Fischer, Pushpendra Singh The particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques are used to study the flow induced on the surface of a salt waterbody when a drop impinges on the surface. The measurements show that the impingement of a fresh water drop causes a strong axisymmetric solutocapillary flow about the vertical line passing through the center of impact. The fluid directly below the center of impact rises upward, and near the surface it moves away from the center of impact. The flow, which develops within a fraction of second after the impact, persists for several seconds and the volume of water circulated is two orders of magnitude larger than the volume circulated when a freshwater drop falls on a freshwater body. [Preview Abstract] |
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KP1.00082: Origin of the Earth's Electromagnetic Field Based on the Pulsating Mantle Hypothesis (PMH) Hassan Gholibeigian In PMH, the Earth's Inner Core's Dislocation (ICD) and Outer Core's Bulge (OCB) phenomena are generated by unbalanced gravitational fields of the Sun and Moon on the Earth. Distance between the Earth's center and inner core's center varies permanently in magnitude and direction inside two hemispheres. Geometrical loci of the inner core's center has the shape of back and force spiral cone in each hemisphere. In other words, the inner core is rotating fast in the outer core inverse of the Earth's rotation a round per day. This mechanism speed up the processes inside the core and generates a Large Scale Forced Convection System (LSFCS) inverse of the Earth's rotation in the core. The LSFCS is the origin of the Earth's electromagnetic field. The LSFCS generates huge mass transfer and momentum of inertia inside the Earth too. The inner core's axis which is the Earth's electromagnetic axis doesn't cross the Earth's geophysical axis and rotates around it per day. The mechanism of this LSFCS has diurnal, monthly and yearly cycles. These cycles are sources of the Earth's electromagnetic field variability. Direction of the variable Earth's magnetic field lines from the South Pole (hemisphere) to the sky and 146 seconds/years apparent solar day length variations can be two observable factors for this mechanism. This dynamic system may occurred inside the other planets like the Sun and the Jupiter. [Preview Abstract] |
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KP1.00083: Tracer filamentation at an unstable ocean front Yen Chia Feng, Amala Mahadevan, Jean-Luc Thiffeault, Philip Yecko A front, where two bodies of ocean water with different physical properties meet, can become unstable and lead to a flow with high strain rate and vorticity. Phytoplankton and other oceanic tracers are stirred into filaments by such flow fields, as can often be seen in satellite imagery. The stretching and folding of a tracer by a two-dimensional flow field has been well studied. In the ocean, however, the vertical shear of horizontal velocity is typically two orders of magnitude larger than the horizontal velocity gradient. Theoretical calculations show that vertical shear alters the way in which horizontal strain affects the tracer, resulting in thin, sloping structures in the tracer field. Using a non-hydrostatic ocean model of an unstable ocean front, we simulate tracer filamentation to identify the effect of vertical shear on the deformation of the tracer. In a complementary laboratory experiment, we generate a simple, vertically sheared strain flow and use dye and particle image velocimetry to quantify the filamentary structures in terms of the strain and shear. We identify how vertical shear alters the tracer filaments and infer how the evolution of tracers in the ocean will differ from the idealized two-dimensional paradigm. [Preview Abstract] |
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KP1.00084: 3D-PTV measurements of jet flow between parallel flat plates Hiroki Kubo, Tatsuro Suzuki, Jun Sakakibara Jet flow in between parallel flat plates was studied experimentally. Flow measurements are carried out using the three-dimensional particle tracking velocimetry (3D-PTV), which allows to measure three dimensional three components of velocity vectors. The plates were rectangular, and separated by 10 mm gap. The nozzle having a square cross-section was installed at an edge of the parallel plates and air was issued into the gap. Downstream evolution of centerline mean velocity, half value width and jet momentum decay will be presented. [Preview Abstract] |
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KP1.00085: An adaptive control process for the temporal shaping of a jet in cross flow Stephen Schein, Takeshi Shoji, Ann Karagozian, Robert M'Closkey This study demonstrates an iterative process for shaping the temporal exit velocity for a gaseous jet in crossflow (JICF). Alternative temporal velocity waveforms, typically measured via hotwire anemometry at the center of the nozzle exit, can significantly affect JICF mixing characteristics\footnote{Shoji, T., Ph.D. Dissertation, UCLA, 2017}. The most challenging waveforms to create are those with rapid transitions in the jet velocity, e.g., single- and double-pulse square waves. While linear models of the jet velocity actuation can be empirically determined and used, in practice they yield poor reproductions of the desired waveforms because the jet velocity is a highly nonlinear function of the actuation variable. This research presents an approach to improve waveform control by using the periodicity of the desired velocity deviation relative to the mean jet velocity. A local model relating perturbations of the harmonics in the input variable to jet velocity harmonics is empirically determined, providing a means to adjust the input harmonics so that the jet profile converges to the desired signal. The process is necessarily iterative because the local model must be re-identified at each new operating point, but the scheme converges rapidly under a variety of flow conditions. [Preview Abstract] |
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KP1.00086: High-Efficiency Multiscale Modeling of Cell Deformations in Confined Microenvironments in Microcirculation and Microfluidic Devices Huijie Lu, Zhangli Peng Our goal is to develop a high-efficiency multiscale modeling method to predict the stress and deformation of cells during the interactions with their microenvironments in microcirculation and microfluidic devices, including red blood cells (RBCs) and circulating tumor cells (CTCs). There are more than 1 billion people in the world suffering from RBC diseases, e.g. anemia, sickle cell diseases, and malaria. The mechanical properties of RBCs are changed in these diseases due to molecular structure alternations, which is not only important for understanding the disease pathology but also provides an opportunity for diagnostics. On the other hand, the mechanical properties of cancer cells are also altered compared to healthy cells. This can lead to acquired ability to cross the narrow capillary networks and endothelial gaps, which is crucial for metastasis, the leading cause of cancer mortality. Therefore, it is important to predict the deformation and stress of RBCs and CTCs in microcirculations. We are developing a high-efficiency multiscale model of cell-fluid interaction to study these two topics. [Preview Abstract] |
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KP1.00087: Nonlinear electrokinetic phenomena in insulator-based dielectrophoretic microdevices. Zhijian Liu, Di Li, Xiangchun Xuan Insulator-based dielectrophoresis (iDEP) is an emerging technology that has been widely used to manipulate particles and cells in microfluidic devices. However, the presence of in-channel insulators can cause two simultaneous nonlinear electrokinetic phenomena that may strongly disturb the linear electrokinetic flow and affect the particle and cell manipulation in iDEP microdevices: one is electrothermal flow due to the amplified Joule heating in the fluid around the insulators, and the other is induced charge electroosmotic (ICEO) flow due to the electrical polarization of the insulators. We study these nonlinear phenomena in the electrokinetic flow of buffer solutions with varying molecular concentrations through a constriction microchannel We find that the ICEO and electrothermal flows are dominant in low and high ionic concentration fluids, respectively. Increasing the magnitude of electric field can also change the flow from ICEO to electrothermal in low concentration fluids. [Preview Abstract] |
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KP1.00088: Strategic obstacle placement reduces drop breakup probability in concentrated emulsion flowing into a constriction Jian Wei Khor, Yu Hua, Alison Bick, Sindy Tang In this study, we investigate the effect of an obstacle on the breakup probability of droplets within a concentrated emulsion flowing into a constriction. We introduce a concentrated emulsion as a 2D monolayer through a tapered channel into a narrow constriction. This geometry is commonly used for the serial interrogation of droplet content in droplet microfluidics applications. We found that certain drop-drop interactions near the constriction entrance lead to the breakup of these drops at a high flow rates. Such breakup sets the upper limit for the droplet interrogation throughput. Incidentally, previous findings have shown that strategic placement of a circular post near a narrow exit can reduce the conflict from the interactions among living organisms (humans, ants, and sheep) or a cluster of particles when entering a narrow exit. Inspired by these results, we modify the tapered channel by placing a circular post in a strategic location near the constriction entrance in order to reduce catastrophic drop-drop interactions and to avoid breakup. Preliminary work shows that the circular posts can reduce the breakup fraction of drops by up to 17{\%}. The optimization of the location and size of the obstacle is expected to further reduce the breakup fraction. [Preview Abstract] |
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KP1.00089: Probing wetting at the nanoscale Kevin Lippera, Caroline Mortagne, Thierry Ondarcuhu, Michael Benzaquen Understanding the physics of wetting is a major issue which comes into play in many applications such as smart materials and bio-mechanical research. The aim of the present work is to study wetting at the nano-scale using Atomic Force Microscopy (AFM). To serve as AFM tips, we design very specific nano-needles with radii below 100 nm fitted with controlled nanometric defects. Dipping the tips into a liquid and using the FM-AFM mode, we are able to monitor the forces and the dissipation induced by the dynamics of the nano-meniscus anchored on the defects. We develop a theoretical model successful at reproducing more than 90 experiments with different liquids, tips and defect sizes. This unprecedented technique coupled with robust theoretical modeling is very promising to address still unanswered questions such as the dissipation of moving contact lines, and in particular confront the Cox-Voinov and de Gennes models. [Preview Abstract] |
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KP1.00090: High throughput separation of live microalgae Endre Joachim Mossige, Atle Jensen A high throughput microfluidic device is used to separate live algal cells of distinctively different shape and size. We demonstrate separation and concentration of four different cell types, shaped like rods, spheres or disks. Our results are compared to results obtained using rigid spheres. We identify different separation modes by streakline visualizations that depend on the size and shape of spheres and algal cells. By tuning the flow field, the concentration ratio is maximized for each type of particle. Our results show that the majority of cells separate with higher concentration ratios than rigid spheres of similar size. We present a second order relation between size and concentration ratio for test spheres and demonstrate excellent agreement with the data points ($R^2$=0.9997). Velocity measurements by $\mu$PIV and PTV show that fluid and particle inertia is necessary for separation. [Preview Abstract] |
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KP1.00091: Load Balancing Strategies for Multiphase Flows on Structured Grids Kristopher Olshefski, Mark Owkes The computation time required to perform large simulations of complex systems is currently one of the leading bottlenecks of computational research. Parallelization allows multiple processing cores to perform calculations simultaneously and reduces computational times. However, load imbalances between processors waste computing resources as processors wait for others to complete imbalanced tasks. In multiphase flows, these imbalances arise due to the additional computational effort required at the gas-liquid interface. However, many current load balancing schemes are only designed for unstructured grid applications. The purpose of this research is to develop a load balancing strategy while maintaining the simplicity of a structured grid. Several approaches are investigated including brute force oversubscription, node oversubscription through Message Passing Interface (MPI) commands, and shared memory load balancing using OpenMP. Each of these strategies are tested with a simple one-dimensional model prior to implementation into the three-dimensional NGA code. Current results show load balancing will reduce computational time by at least 30\%. [Preview Abstract] |
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KP1.00092: Unstructured Finite Elements and Dynamic Meshing for Explicit Phase Tracking in Multiphase Problems Anirban Chandra, Fan Yang, Yu Zhang, Ehsan Shams, Onkar Sahni, Assad Oberai, Mark Shephard Multi-phase processes involving phase change at interfaces, such as evaporation of a liquid or combustion of a solid, represent an interesting class of problems with varied applications. Large density ratio across phases, discontinuous fields at the interface and rapidly evolving geometries are some of the inherent challenges which influence the numerical modeling of multi-phase phase change problems. In this work, a mathematically consistent and robust computational approach to address these issues is presented. We use stabilized finite element methods on mixed topology unstructured grids for solving the compressible Navier-Stokes equations. Appropriate jump conditions derived from conservations laws across the interface are handled by using discontinuous interpolations, while the continuity of temperature and tangential velocity is enforced using a penalty parameter. The arbitrary Lagrangian-Eulerian (ALE) technique is utilized to explicitly track the interface motion. Mesh at the interface is constrained to move with the interface while elsewhere it is moved using the linear elasticity analogy. Repositioning is applied to the layered mesh that maintains its structure and normal resolution. In addition, mesh modification is used to preserve the quality of the volumetric mesh. [Preview Abstract] |
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KP1.00093: Comparison of LES and PIV Velocity Fields in a Complex Multi-Stream Supersonic Nozzle Samuel Banahene, Harry Winick, Mattew Berry, Andrew Tenney, Mark Glauser, Cory Stack, Datta Gaitonde, Christopher Ruscher, Andrew Magstadt Two independent Large Eddy Simulations (LES) were conducted on a Mach $=$ 1.6 rectangular multi-stream nozzle. PIV data was taken on the same nozzle for the purposes of experimental validation. We will compare centerline velocity measurements from these data sets at various downstream locations. Mean and RMS velocity contours and profiles from these LES data sets show reasonable agreement with PIV data. Shear layer growth rates will also be compared between the experimental and computational visualizations. Based on the acquired velocity contours, it appears that both LES data sets slightly overestimate shear layer growth in the jet plume. Velocity spectra will be extracted from the LES time-series for comparison between these two independent studies. Flow over the aft-deck of the nozzle appears similar between all data sets, with the exception that the LES data seems to overemphasize boundary layer growth. [Preview Abstract] |
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KP1.00094: New Turbulent Multiphase Flow Facilities for Simulation Benchmarking Chee Hau Teoh, Ashwanth Salibindla, Ashik Ullah Mohammad Masuk, Rui Ni The Fluid Transport Lab at Penn State has devoted last few years on developing new experimental facilities to unveil the underlying physics of coupling between solid-gas and gas-liquid multiphase flow in a turbulent environment. In this poster, I will introduce one bubbly flow facility and one dusty flow facility for validating and verifying simulation results. [Preview Abstract] |
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KP1.00095: Hopping Diffusion of Nanoparticles in Polymer Solutions: Non-Gaussian Stochastic Nature and Typical Timescale Xu Zheng, Chundong Xue, Guoqing Hu The diffusion of nanoparticles (NPs) in crowded and heterogeneous environments is intriguing as it presents the mesoscopic behavior distinct from the classical Brownian motion. It is of great interest to explore how NPs are able to hop through such crowded networks. In this study, we present experimental results to demonstrate the occurrence of hopping diffusion and characterize the typical timescale of hopping dynamics in entangled polymer solutions. Current experiments focus on the hopping behavior of “large” NPs subjected to the constraint in entangled polymer solutions. Thus, we clarify the non-Gaussian stochastic nature and the time-varied tendency of the hopping dynamics in polymer solutions. We establish a scaling law of the hopping time scale $\tau_{\mathrm{hop}}$. The time-varied non-Gaussianity reveals the prevalence of the competition among the short-time relaxation of polymer entanglement strand, the hopping dynamics, and the long-time reptation. The hopping motion of large NPs in entangled polymer solutions occurs only when $\tau_{\mathrm{hop\thinspace }}$is larger than the entanglement timescale but smaller than the reptation timescale, and it is attributed to the thermally activated process by overcoming the free energy barrier. [Preview Abstract] |
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KP1.00096: Perspectives on continuum flow models for force-driven nano-channel liquid flows Ali Beskok, Jafar Ghorbanian, Alper Celebi A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs. [Preview Abstract] |
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KP1.00097: Ion transport in self-assembled 2D nanofluidic channels constructed by graphene oxide sheets cross-linked with glyoxal and ethylenediamine monomers. Chih-Chang Chang, Wei-Hao Huang Graphene oxide (GO) sheets in aqueous solution becomes negatively charged due to the dissociation of surface functional group (e.g., -OH, -COOH). Therefore, the membrane constructed by GO sheets would disintegrate owing to electrostatic repulsion. In this work, two monomers (glyoxal and ethylenediamine) were used for cross-linking GO sheets to construct composite graphene oxide-framework (GOF) membranes with 2D nanofluidic channels through the vacuum filtration method. Results of X-ray diffraction (XRD) showed that~$d$-spacing in GOF layers (nanochannel size) is tuned to a value of approximately 1 nm in wet state.~The stretching of $d$-spacing could be effectively suppressed and the stability of GOF membranes in aqueous solution was greatly improved. Finally, the ion transport and nonlinear current-voltage characteristics of these GOF membranes in salt (KCl) solution were investigated experimentally. The results showed that ion transport through GOF membrane begins to deviate from bulk behavior up to the salt concentration of 0.01M and gradually plateaus at low salt concentrations, i.e., the surface-charge-governed ion transport in 2D GOF nanofluidic channels. The nonlinear $I-V$ characteristic of GOF membranes due to concentration polarization was also observed. [Preview Abstract] |
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KP1.00098: Effects of surface group deprotonation on the water desalination by graphene oxide membranes Chao Fang, Zhou Yu, Rui Qiao Graphene-based membranes have shown great potential in enabling highly efficient water desalination from salty water. Effectively engineering these membranes necessitates a fundamental understanding of how the molecular structure and chemical details of the nanopores in these membranes govern the transport of water and ions through them. Here, we use molecular dynamics simulations to investigate how deprotonation of the carboxyl groups along the perimeter of the nanopores in single-layer graphene oxide membranes affects the water transport and salt leakage through these pores. Modest deprotonation lowers the energy barrier for water translocation through the pores and thus enhances the water flux; too strong a deprotonation, however, reduces the water flux by slowing down the dynamics of water molecules inside the pores. These effects are pronounced for pores with a diameter of 0.68nm but is weak for pores with a diameter of 1.12nm. Deprotonation only modestly increases the ion leakage through the nanopores. These results suggest that the deprotonation of the surface groups in graphene oxide membranes may be tailored to improve the performance of these membranes. [Preview Abstract] |
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KP1.00099: Probing the Chaotic Dynamics of Fluids using Insights from Coupled Map Lattices Johnathon Barbish, Mu Xu, Mark Paul Many difficult fluid challenges exhibit high-dimensional spatiotemporal chaos. Natural examples include the dynamics of the atmosphere and oceans. New insights have been gained by studying canonical fluid problems such as Rayleigh-B\'{e}nard convection where significant progress has been made using large-scale computations of the partial differential equations that describe the fluid flow. However, these computations remain very expensive which makes it difficult, if not currently impossible, to explore new ideas that require large sample sets, vast sweeps of parameter space, and long-time statistics. We study these questions using coupled map lattices (CML) in one and two dimensions. We compute the covariant Lyapunov vectors to probe fundamental features of the CML's including the Lyapunov spectrum, fractal dimension, and the principal angle between the stable and unstable manifolds. We are particularly interested in the role of a conservation law on the chaotic dynamics, the use of ideas from equilibrium thermodynamics to yield a coarse-grained representation, and in the development of reduced order models. [Preview Abstract] |
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KP1.00100: Transport in the Stochastic Lorenz System Scott Weady, Sahil Agarwal, Larry Wilen, John Wettlaufer We study transport in the stochastic Lorenz system mathematically, computationally and using a circuit model. The circuit model provides a very efficient method for computing long time averages of polynomials in the variables $X,Y,$ and $Z$ with real-time updates. In particular, we use this approach to the quantity $\langle XY \rangle$, which is the heat transport corresponding with Rayleigh-B\'enard convection. We interpret our results in the framework of analytical stochastic upper bounds [1] for $\langle XY \rangle$ versus $\rho$ (the reduced Rayleigh number), as well as against numerical solutions. For a given $\rho$ we find a rich dependence of the transport on both noise color and amplitude due to the detailed coupling of noise with Unstable Periodic Orbits.\\ {\bf [1]} {S. Agarwal and J. S. Wettlaufer, Maximal stochastic transport in the Lorenz equations, {\em Phys. Lett. A} {\bf 380}, 142 (2016).} [Preview Abstract] |
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KP1.00101: Boundary layer streaming in viscoelastic fluids Seyed Amir Bahrani, Maxime Costalanga, Laurent Royon, Philippe Brunet Oscillations of bodies immersed in fluids are known to generate secondary steady flows (streaming). These flows have strong similarities with acoustic streaming induced by sound and ultrasound waves. A typical situation, investigated here, is that of a cylinder oscillating perpendicular to its axis, generating two pairs of counter-rotating steady vortices due to the transfer of vorticity from an inner boundary layer. While most studies so far investigated the situation of newtonian fluids, here, we consider the situation of a viscoelastic fluid. By using Particle Image Velocimetry, we carry out an experimental study of the flow structure and magnitude over a range of amplitude (A up to 2.5 mm, nearly half the cylinder diameter) and frequency (f between 5 and 100 Hz). We observe unprecedented behaviors at higher frequency (f \textgreater 50 Hz) : at high enough amplitude, the usual flow with 2 pairs of vortices is replaced by a more complex flow where 4 pairs of vortices are observed. At smaller frequency, we observe reversal large scale vortices that replace the usual inner and outer ones in Newtonian fluids. The main intention of this work is to understand the influence of the complex and nonlinear rheology on the mechanism of streaming flow. In this way, another source of purely rheological nonlinearity is expected, competing with hydrodynamic nonlinearity. We evidence the effect of elasticity in streaming. [Preview Abstract] |
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KP1.00102: Dynamics and structures of transitional viscoelastic turbulence in channel flow Ashwin Shekar, Sung-Ning Wang, Michael Graham Introducing a trace amount of polymer into turbulent flows can result in a substantial reduction of drag. However, the mechanism is not fully understood at high levels of drag reduction. In this work we perform direct numerical simulations (DNS) of viscoelastic channel flow turbulence using a scheme that guarantees the positive-definiteness of polymer conformation tensor without artificial diffusion. Here we present the results of two parametric studies with the bulk Reynolds number fixed at 2000. First, the Weissenberg number (Wi) is kept at 100 and we vary the viscosity ratio (ratio ratio of the solvent viscosity and the total viscosity). Maximum drag reduction (MDR) is observed with viscosity ratio \textless 0.95. As we decrease the viscosity ratio, i.e. increase polymer concentration, the mean velocity profile is almost invariant. However, this is accompanied by a decrease in velocity fluctuations but the flow stays turbulent. Turbulent kinetic energy budget analysis shows that, in this parameter regime, polymer becomes the major source of velocity fluctuations, replacing the energy transfer from the mean flow. In the second study, we fix the viscosity ratio at 0.95 and trace the Wi up to this regime and present the accompanying changes in flow quantities and structures. [Preview Abstract] |
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KP1.00103: Boundary layer in flow of Shear-dependent-viscosity fluids between parallel plates nariman ashrafi, Ali Sadeghi, Mehdi Shafahi Formation of the boundary layer in the laminar flow of Herschel--Bulkley fluid between parallel plates is taken into consideration . In particular, the study is focused on the flow of the shear thinning and shear thickening fluids past a partial vertical wall in between the plates. Upon numerically solving the continuity and momentum equations the flow is analyzed throughout the domain using a finite volume scheme. The shear stress at the wall together with velocity distribution are evaluated and compared with experimental results for several values of Herschel-Bulkley coefficients for fluidity and flow behavior index. [Preview Abstract] |
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KP1.00104: Modelling dynamic transport and adsorption of arsenic in soil-bed filters for long-term performance evaluation Sourav Mondal, Raka Mondal, Sirshendu De, Ian Griffiths Purification of contaminated water following the safe water guidelines while generating sufficiently large throughput is a crucial requirement for the steady supply of safe water to large populations. Adsorption-based filtration processes using a multilayer soil bed has been posed as a viable method to achieve this goal. This work describes the theory of operation and prediction of the long-term behaviour of such a system. The fixed-bed column has a single input of contaminated water from the top and an output from the bottom. As the contaminant passes through the column, it is adsorbed by the medium. Like any other adsorption medium, the filter has a certain lifespan, beyond which the filtrate does not meet the safe limit of drinking water, which is defined as `breakthrough'. A mathematical model is developed that couples the fluid flow through the porous medium to the convective, diffusive and adsorptive transport of the contaminant. The results are validated with experimental observations and the model is then used to predict the breakthrough and lifetime of the filter. The key advantage of this model is that it can predict the long-term behaviour of any adsorption column system for any set of physical characteristics of the system. [Preview Abstract] |
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KP1.00105: Pattern formation study of dissolution-driven convection Noufe Aljahdaly, Layachi Hadji A three-dimensional pattern formation analysis is performed to investigate the dissolution-driven convection induced by the sequestration of carbon dioxide. We model this situation by considering a Rayleigh-Taylor like base state consisting of carbon-rich heavy brine overlying a carbon-free layer and seek, through a linear stability analysis, the instability threshold conditions as function of the thickness of the CO$_2$-rich brine layer. Our model accounts for carbon diffusion anisotropy, permeability dependence on depth and the presence of a first order chemical reaction between the carbon-rich brine and host mineralogy. A small amplitude nonlinear stability analysis is performed to isolate the preferred regular pattern and solute flux conditions at the interface. The latter are used to derive equations for the time and space evolution of the interface as it migrates upward. We quantify the terminal time when the interface reaches the top boundary as function of the type of solute boundary conditions at the top boundary thereby also quantifying the beginning of the shutdown regime. The analysis will also shed light on the development of the three-dimensional fingering pattern that is observed when the constant flux regime is attained. [Preview Abstract] |
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KP1.00106: A data driven model for the impact of IFT and density variations on CO$_{\mathrm{2}}$ sequestration in porous media Mohammad Nomeli, Amir Riaz CO$_{\mathrm{2}}$ storage in geological formations is one of the most promising solutions for mitigating the amount of greenhouse gases released into the atmosphere. One of the important issues for CO$_{\mathrm{2}}$ storage in subsurface environments is the sealing efficiency of low-permeable cap-rocks overlying potential CO$_{\mathrm{2}}$ storage reservoirs. A novel model is proposed to find the IFT of the systems (CO$_{\mathrm{2}}$/brine-salt) in a range of temperatures (300-373 K), pressures (50-250 bar), and up to 6 molal salinity applicable to CO$_{\mathrm{2}}$ storage in geological formations through a machine learning-assisted modeling of experimental data. The IFT between mineral surfaces and CO$_{\mathrm{2}}$/brine-salt solutions determines the efficiency of enhanced oil or gas recovery operations as well as our ability to inject and store CO$_{\mathrm{2}}$ in geological formations. Finally, we use the new model to evaluate the effects of formation depth on the actual efficiency of CO$_{\mathrm{2}}$ storage. The results indicate that, in the case of CO$_{\mathrm{2}}$ storage in deep subsurface environments as a global-warming mitigation strategy, CO$_{\mathrm{2}}$ storage capacity are improved with reservoir depth. [Preview Abstract] |
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KP1.00107: Thin film dynamics and its effect on two phase flow in porous media Yaniv Edery, Steffen Berg, David Weitz We show with confocal microscopy that thin films for both imbibition and drainage serve as conduit to seemingly isolated oil ganglia. Interfacial drag forces on these thin films move fluid from one ganglion to the other leading to destabilization of capillary forces over long-time scales. Using unique experimental setup, we quantify the effect of thin film flow between ganglia. This shows that the physics of two phase flow in porous media is far richer than geometry coupled with capillary forces alone. [Preview Abstract] |
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KP1.00108: Simultaneous two-phase flow measurement techniques using Particle Image Velocimetry. Hadis Matinpour, Joseph Atkinson, Sean Bennett Most geophysical and environmental flows in nature are turbulent flow and entrain suspended sediments. Turbulent-sediment interaction is one of the most challenging and complicated phenomenon. Many studies have investigated turbulent modulation by suspended sediments. However, there is little investigation on studying sediments in suspension as a two-phase flow, one phase of sediments and another phase of fluid. In this study, we designed and employed a state-of-the-art two-phase PIV method to measure each phase instantaneous velocities simultaneously and separately. The technique that we have developed is employing a computer-vision based method, which enables us to discriminate sediment particles from fluid tracer particles based on two thresholds, dissimilar particle sizes and different particle intensities. To validate two-phase PIV method, we also measured only fluid phase velocities by florescent tracer particles and a camera equipped with a narrow-band filter. Results from imaged processing method are compared with results from physically discriminated two phase method. [Preview Abstract] |
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KP1.00109: Preferential Concentration Of Solid Particles In Turbulent Horizontal Circular Pipe Flow Jaehee Kim, Kyung-Soo Yang In particle-laden turbulent pipe flow, turbophoresis can lead to a preferential concentration of particles near the wall. To investigate this phenomenon, one-way coupled Direct Numerical Simulation (DNS) has been performed. Fully-developed turbulent pipe flow of the carrier fluid (air) is at $Re_{\tau } =200$ based on the pipe radius and the mean friction velocity, whereas the Stokes numbers of the particles (solid) are $St^{+}=\,0.1,\,\,1,\,\,10$ based on the mean friction velocity and the kinematic viscosity of the fluid. The computational domain for particle simulation is extended along the axial direction by duplicating the domain of the fluid simulation. By doing so, particle statistics in the spatially developing region as well as in the fully-developed region can be obtained. Accumulation of particles has been noticed at $St^{+}\,=\,$1 and 10 mostly in the viscous sublayer, more intensive in the latter case. Compared with other authors' previous results, our results suggest that drag force on the particles should be computed by using an empirical correlation and a higher-order interpolation scheme even in a low-Re regime in order to improve the accuracy of particle simulation. [Preview Abstract] |
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KP1.00110: Modeling and Simulation of Swirl Stabilized Turbulent Non-Premixed Flames Salvador Badillo-Rios, Ann Karagozian Flame stabilization is an important design criterion for many combustion chambers, especially at lean conditions and/or high power output, where insufficient stabilization can result in dangerous oscillations and noisy or damaged combustors. At high flow rates, swirling flow can offer a suitable stabilization mechanism, although understanding the dynamics of swirl-stabilized turbulent flames remains a significant challenge. Utilizing the General Equation and Mesh Solver (GEMS) code, which solves the Navier-Stokes equations along with the energy equation and five species equations, 2D axisymmetric and full 3D parametric studies and simulations are performed to guide the design and development of an experimental swirl combustor configuration and to study the effects of swirl on statistically stationary combustion. Results show that as the momentum of air is directed into the inner air inlet rather than the outer inlet of the swirl combustor, the central recirculating region becomes stronger and more unsteady, improving mixing and burning efficiency in that region. A high temperature region is found to occur as a result of burning of the trapped fuel from the central toroidal vortex. The effects of other parameters on flowfield and flame-stabilization dynamics are explored. [Preview Abstract] |
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KP1.00111: A novel device for hydrodynamic separation of inertial particles Lydia M. Tsiverioti, Mahdi Esmaily, Ali Mani Current methods of particle separation, ranging from filtration devices to cyclones are inadequate in terms of maintenance or precision, respectively. A recent analytical work has shown that inertial particles placed in a flow that is temporally and spatially varying, exhibit extremely different behavior for a slight change in their size. In such flows, particles of a certain size can form cluster whereas particles that are larger in diameter by as low as 1% can disperse. The objective of this study is to employ this phenomenon and design a device that produces a suitable flow for the realization of this phenomenon. In this poster, we describe our numerical method that was developed to produce an initial design. We then demonstrate that the computed geometry is conducive to particle separation by performing CFD simulations. Finally, we predict the operating regime of this device by computing the diameter and density of the particles that can be separated in practice. [Preview Abstract] |
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KP1.00112: The fluid mechanics of channel fracturing flows: experiment Ahmadreza Rashedi, Zachery Tucker, Guillaume Ovarlez, Sarah Hormozi We show our preliminary experimental results on the role of fluid mechanics in channel fracturing flows, particularly yield stress fracturing fluids. Recent trends in the oil industry have included the use of cyclic pumping of a proppant slurry interspersed with a yield stress fracturing fluid, which is found to increase wells productivity, if particles disperse in a certain fashion. Our experimental study aims to investigate the physical mechanisms responsible for dispersing the particles (proppant) within a yield stress carrier fluid, and to measure the dispersion of proppant slugs in various fracturing regimes. To this end we have designed and built~a unique experimental setup that resembles a fracture configuration coupled with a particle image/tracking velocimetry setup operating at micro to macro dimensions. Moreover, we have designed optically engineered suspensions of complex fluids with tunable yield stress and consistency, well controlled density match-mismatch properties and refractive indices for both X-rays and visible lights. We present our experimental system and preliminary results. [Preview Abstract] |
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KP1.00113: Understanding Core Collapse Through Dynamic Mode Decomposition Halley Aycock-Rizzo, Mohd Ali, Andrew Tenney, Matthew Berry, Zachary Berger, Mark Glauser The column mode (or preferred mode) and the shear layer mode in an axisymmetric high subsonic jet are analyzed using Dynamic Mode Decomposition (DMD) to study their relation to core collapse and instability. High frequency pressure sensor data at the exit of the jet are correlated to dominant DMD amplitudes. We focus on two spatial regions of interest: before and after core collapse. In the former, we investigate the contribution of both modes as they interact with the structure of the jet, and in the latter, where we find no shear layer mode, we are able to find remnants of the column mode and account for instability in terms of its evolution. Observations of the jet at different Mach numbers allow us to draw conclusions about core collapse in terms of the structure of the column mode in the transition between these two regions. [Preview Abstract] |
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KP1.00114: An analogy between the merger of two black holes and the collision of two point-vortices Maria Barbara El Fakhri, Giuseppe Di Labbio, Lyes Kadem, Hoi Dick Ng, Hamid Ait Abderrahmane This work is an attempt to produce an analogy between the merger of two black holes and the collision of two point-vortices produced in a shallow water layer. The former collision generates gravitational waves propagating at the speed of light, while the latter creates waves propagating along the free surface. The two point-vortices are generated by spinning two small magnetic discs. The vortices were brought to collide by displacing the spinning discs toward each other at several constant speeds. The resulting flow dynamics and surface waves were quantitatively investigated using particle image velocimetry measurements and interferometry. [Preview Abstract] |
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KP1.00115: A mechanism of thrust enhancement on a heaving plate due to flexibility at moderately low Reynolds numbers Yung-Sheng Lin, Yau-Ting Tzeng, Chien-Cheng Chang, Chin-Chou Chu A numerical study is conducted to investigate the force mechanisms for a 3D heaving flexible plate from the perspective of a diagnostic force element analysis (Chang 1992). The problem is relevant to a simplified flapping fish-tail with the front edge held fixed in space. The flow is assumed to be laminar with the Reynolds numbers fixed at Re$=$200 or 500, and the Strouhal number St ranging from 0.1 to 0.6, and the flexure amplitude of the plate a0 for 0.1 to 0.25 (dimensionless). It is shown that heaving, whilst increasing thrust generation, also reduces the frictional drag, yet the flexibility promotes thrust generation at the expense of accruing more frictional drag. In the literature, the thrust exerted on the tail-mimicking plate is largely credited to the vortices in the wake. However, this study performs a regional force analysis to show that the vorticity in the wake region supplies approximately 20-30{\%} of the total thrust, especially in the cases of strong thrust generation. Comparable contributions come also from the regions direct above and below the heaving plate (mainly including the attached vortices) as well as from the two side regions (mainly including the tip vortices) next to the flapping plate. In addition, the potential motion associated with the unsteady flapping and the contribution from the surface vorticity are non-negligible constituent force components. [Preview Abstract] |
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KP1.00116: Dynamics and stability of a 2D ideal vortex under external strain N. C. Hurst, J. R. Danielson, D. H. E. Dubin, C. M. Surko The behavior of an initially axisymmetric 2D ideal vortex under an externally imposed strain flow is studied experimentally [1]. The experiments are carried out using electron plasmas confined in a Penning-Malmberg trap; here, the dynamics of the plasma density transverse to the field are directly analogous to the dynamics of vorticity in a 2D ideal fluid. An external strain flow is applied using boundary conditions in a way that is consistent with 2D fluid dynamics. Data are compared to predictions from a theory assuming a piecewise constant elliptical vorticity distribution [2]. Excellent agreement is found for quasi-flat profiles, whereas the dynamics of smooth profiles feature modified stability limits and inviscid damping of periodic elliptical distortions. [1] N. C. Hurst, et. al., Phys. Rev. Lett. 117, 235001 (2016). [2] S. Kida, J. Phys. Soc. Japan 50, 3517 (1981). [Preview Abstract] |
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KP1.00117: Point vortex dynamics on a toroidal surface Takashi Sakajo, Yuuki Shimizu Interactions of vortex structures play an important role in the understanding of complex evolutions of fluid flows. Incompressible and inviscid flows with point-wise vorticity distributions in two-dimensional space, called point vortices, have been used as a theoretical model to describe such vortex interactions. The motion of point vortices has been investigated well in unbounded planes with boundaries as well as on a sphere owing to their physical relevance. On the other hand, it is of a theoretical interest to investigate how geometric nature of curved surfaces and the number of holes gives rise to different vortex interactions that are not observed in vortex dynamics in the plane and on the sphere. In the preceding studies, point-vortex interactions on surfaces of revolution have been investigated. In this presentation, we derive the equation of motion of point vortices on a toroidal surface, which is a compact, orientable 2D Riemannian manifold with a non-constant curvature with one handle. We then investigate the motion of two point vortices and the stability analysis of a latitudinal ring configuration of $N$ point vortices. [Preview Abstract] |
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KP1.00118: Vortex breakdown of compressible swirling flows in a pipe Harry Lee, Zvi Rusak, Shixiao Wang The manifold of branches of steady and axisymmetric states of compressible subsonic swirling flows in a finite-length straight circular pipe are developed. The analysis is based on Rusak et al. (2015) nonlinear partial differential equation for the solution of the flow stream function in terms of the inlet flow total enthalpy, entropy and circulation functions. This equation reflects the complicated thermo–physical interactions in the flows. The flow problem is solved numerically using a finite difference approach with a penalty procedure for identifying vortex breakdown and wall-separation states. Several types of solutions are found and used to form the bifurcation diagram of steady compressible flows with swirl as the inlet swirl level is increased at a fixed inlet Mach number. Results are compared with predictions from the global analysis approach of Rusak et al. (2015). The computed results provide theoretical predictions of the critical swirl levels for the first appearance of vortex breakdown states as a function of the inlet Mach number. The shows the delay in the appearance of breakdown with increase of the inlet axial flow Mach number in the subsonic range of operation. [Preview Abstract] |
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KP1.00119: Learning to classify wakes from local sensory information Mohamad Alsalman, Brendan Colvert, Eva Kanso Aquatic organisms exhibit remarkable abilities to sense local flow signals contained in their fluid environment and to surmise the origins~of these flows. For example, fish can discern the~information contained in various flow structures and utilize this~information for obstacle avoidance~and prey tracking. Flow structures created by flapping and swimming bodies are well~characterized in~the fluid dynamics literature; however, such characterization relies on classical methods that use an~external observer to~reconstruct global flow fields. The reconstructed flows, or wakes, are then classified according to the unsteady vortex patterns. Here,~we propose a new approach for wake identification: we~classify the wakes resulting from a flapping~airfoil by applying machine learning algorithms to local~flow information. In particular,~we simulate the wakes of an oscillating airfoil in an~incoming flow, extract the~downstream vorticity information, and train a classifier to learn the different flow structures and classify~new ones. This data-driven approach provides a promising framework for underwater navigation and detection~in application to autonomous bio-inspired vehicles. [Preview Abstract] |
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KP1.00120: The Role of the Separation Point in Streamwise VIV of Cylinders of Various Cross-sectional Shapes Neil Cagney, Stavroula Balabani Vortex-Induced Vibration (VIV) is a classic fluid-structure interaction problem and can lead to fatigue damage and catastrophic failure of bodies in cross-flow. VIV acting in the streamwise (flow) direction is relatively poorly understood compared to that acting in the transverse (lift) direction, but can have a very significant effect of the overall response of structures with two or more degrees of freedom (DOFs). We present time-resolved PIV measurements of the wake and structural response of cylinders with a range of cross-sectional shapes, including circular, elliptical, triangular and square. The response of a circular cylinder is characterised by two response branches, in agreement with previous studies. However, it is shown that for geometries with fixed separation points, no significant VIV is observed and vortex-shedding does not lock-in to the vibration frequency. This finding suggests that the fluid excitation caused by the interaction between the cylinder displacement and the shear layers is reliant on the ability of the separation point to vary. It also suggests that control of the separation points may be an effective means of restricting VIV of multi-DOF bodies. [Preview Abstract] |
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KP1.00121: Vortex trajectory and wake structure behind an energy harvesting hydrofoil Walker Lee, Maximilien de Zordo-Banliat, Yunxing Su, Michael Miller, Kenneth Breuer Detailed knowledge regarding the wake structure behind a pitching and heaving hydrofoil is important for optimizing multi-foil energy harvesting systems. Here we report on measurements of the large vortices shed from the hydrofoil. An acoustic Doppler velocimeter is positioned in a water flume, downstream of a flapping hydrofoil (chord, $c$ = 10 cm) and traversed across the wake, measuring three components of velocity at 25 Hz over at least 20 cycles. The phase-averaged velocities are used to identify the primary vortex structures and to assess their trajectory, intensity and coherence as functions of frequency, $f$, pitching amplitude, $\theta$, and Reynolds number, $Re$. Different methods for identifying the vortex structures are developed and their utility and weakness are compared. It is found that the transverse distance between the shed vortices (i.e. the width of the wake) decreases as the reduced frequency ($fc/U$) rises, but is not sensitive to the pitching amplitude. The time at which a vortex arrives at a fixed downstream position is affected by both the time at the vortex separates from the foil and the vortex convection speed in the wake. These two quantities are assessed as functions of pitch amplitude, reduced frequency and Reynolds number. [Preview Abstract] |
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KP1.00122: DSMC Simulations of High Mach Number Taylor-Couette Flow Dr. Sahadev Pradhan The main focus of this work is to characterise the Taylor-Couette flow of an ideal gas between two coaxial cylinders at Mach number \textit{Ma }$=$\textit{ (U\textunderscore w / }$\backslash $\textit{sqrt\textbraceleft kb T\textunderscore w / m\textbraceright )}in the range 0.01 \textless Ma \textless , and Knudsen number \textit{Kn }$=$\textit{ (1 / (}$\backslash $\textit{sqrt\textbraceleft 2\textbraceright }$\backslash $\textit{pi d\textasciicircum 2 n\textunderscore d (r\textunderscore 2 - r\textunderscore 1))) }in the range 0.001 \textless Kn \textless , using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations. Here, \textit{r\textunderscore 1}and \textit{r\textunderscore 2}are the radius of inner and outer cylinder respectively, \textit{U\textunderscore w}is the circumferential wall velocity of the inner cylinder, \textit{T\textunderscore w}is the isothermal wall temperature, \textit{n\textunderscore d}is the number density of the gas molecules, $m$and $d$ are the molecular mass and diameter, and \textit{kb}is the Boltzmann constant. The cylindrical surfaces are specified as being diffusely reflecting with the thermal accommodation coefficient equal to one. In the present analysis of high Mach number compressible Taylor-Couette flow using DSMC method, wall slip in the temperature and the velocities are found to be significant. Slip occurs because the temperature/velocity of the molecules incident on the wall could be very different from that of the wall, even though the temperature/velocity of the reflected molecules is equal to that of the wall. Due to the high surface speed of the inner cylinder, significant heating of the gas is taking place. The gas temperature increases until the heat transfer to the surface equals the work done in moving the surface. The highest temperature is obtained near the moving surface of the inner cylinder at a radius of about (1.26 r\textunderscore 1). [Preview Abstract] |
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KP1.00123: Microparticle Separation by Cyclonic Separation Keegan Karback, Alexander Leith The ability to separate particles based on their size has wide ranging applications from the industrial to the medical. Currently, cyclonic separators are primarily used in agriculture and manufacturing to syphon out contaminates or products from an air supply. This has led us to believe that cyclonic separation has more applications than the agricultural and industrial. Using the OpenFoam computational package, we were able to determine the flow parameters of a vortex in a cyclonic separator in order to segregate dust particles to a cutoff size of tens of nanometers. To test the model, we constructed an experiment to separate a test dust of various sized particles. We filled a chamber with Arizona test dust and utilized an acoustic suspension technique to segregate particles finer than a coarse cutoff size and introduce them into the cyclonic separation apparatus where they were further separated via a vortex following our computational model. The size of the particles separated from this experiment will be used to further refine our model. [Preview Abstract] |
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KP1.00124: Possible self focusing mechanism of an inertial wave Waleed Mouhali, Thierry Lehner We study inertial wave-wave interaction into an incompressible inviscid rotating fluid, by analyzing a Ginzburg-Landau equation with complex coefficients (asymptotically derived from the relevant Navier-Stokes equation). We compute the wave coupling terms at different orders in wave amplitude, relying on an approximated associated Beltrami property. At third order it is shown that wave self-coupling can lead to wave self-focusing. A short comparison is made with recent experiments. [Preview Abstract] |
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KP1.00125: Experimental Investigation of Dispersive Shock Waves in Shallow Water Adam Binswanger Supersonic flow past a slender wedge is a canonical problem of interest in compressible fluid dynamics. However, the experiments are extremely delicate and require experimental expertise. Simpler experiments in which supercritical shallow water flows past a wedge have been implemented under the auspice of the hydraulic analogy. In doing so, the resulting shock was found to be an oscillatory, steady pattern now understood to be an oblique dispersive shock wave (DSW), paralleling similar phenomena in nonlinear fiber optics, ultra-cold atoms, and internal and surface water waves. We implement a similar shallow water experiment in which a sluice gate controls the shallow flow at supercritical velocities that are deflected by a slim wedge. By measuring phase shifts in a sinusoidal fringe pattern projected on the water surface we can reconstruct a surface profile using the Fourier Transform Profilometry technique. The experimental setup and image processing will be detailed and illustrative experimental surface wave profiles will be given. [Preview Abstract] |
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KP1.00126: Working research codes into fluid dynamics education: a science gateway approach Lachlan Mason, James Hetherington, Martin O'Reilly, May Yong, Radka Jersakova, Stuart Grieve, David Perez-Suarez, Roman Klapaukh, Richard V. Craster, Omar K. Matar Research codes are effective for illustrating complex concepts in educational fluid dynamics courses, compared to textbook examples, an interactive three-dimensional visualisation can bring a problem to life! Various barriers, however, prevent the adoption of research codes in teaching: codes are typically created for highly-specific `once-off' calculations and, as such, have no user interface and a steep learning curve. Moreover, a code may require access to high-performance computing resources that are not readily available in the classroom. This project allows academics to rapidly work research codes into their teaching via a minimalist `science gateway' framework. The gateway is a simple, yet flexible, web interface allowing students to construct and run simulations, as well as view and share their output. Behind the scenes, the common operations of job configuration, submission, monitoring and post-processing are customisable at the level of shell scripting. In this talk, we demonstrate the creation of an example teaching gateway connected to the Code BLUE fluid dynamics software. Student simulations can be run via a third-party cloud computing provider or a local high-performance cluster. [Preview Abstract] |
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KP1.00127: Soda bottle water rockets - a project students (seem to) like Veronica Eliasson In this talk I will present my experience of developing and leading an undergraduate student project for a junior level Fluid Mechanics course. My goal was to let students participate in a project that would help them to develop and retain a better understanding for several fluid mechanics concepts, while simultaneously being challenged in an interesting and fun way. Thus, students were divided into teams and asked to complete two things: 1) determine using theory mixed with numerical estimates how much water to add to the soda bottle given a maximum amount of allowable pressure for their bottle rocket; and 2) design, build and fly a rocket with the goal of reaching as high of an altitude as possible. I'll also talk about the weekly tasks given to students, the results, and finally share some of the comments and perspectives from the participating students. [Preview Abstract] |
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KP1.00128: Validation of A One Dimensional Model for Volumetrically Forced Jets Using Large Eddy Simulations Amitabh Bhattacharya, Chandra Shekhar Pant Volumetrically forced jets are often considered as idealized models for atmospheric clouds. In this work, we use an existing energy-consistent approach for dynamically expressing the entrainment rate constant, $\alpha$, in terms of radial integrals of the velocity field, Reynolds stress field and bouyancy field. We use a mixing length model to relate the Reynolds stress to the velocity gradient. We then construct a one-dimensional (1-D) model for evolving volumetrically forced jets, in which we assume that the radial variation of the axial velocity has a Gaussian shape. The imposed external forcing, with a Gaussian radial profile, is applied within a certain height range, far from the jet inlet. Large Eddy Simulations of forced jets are conducted to validate this 1-D model. We find that the axial velocity deviates significantly from a Gaussian profile if the forcing is confined to a radius that is much smaller than the jet radius; this in turn can lead to discrepancy between the LES and the 1-D model. On the other hand, if the forcing radius is comparable to the jet radius, then the 1-D model agrees well with the LES, even at high forcing Richardson number. The bouyancy flux within the forcing zone is predicted well by the 1-D model for all the cases. [Preview Abstract] |
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KP1.00129: Teaching with Stereoscopic Video: Opportunities and Challenges Evan Variano I will present my work on creating stereoscopic videos for fluid pedagogy. I discuss a variety of workflows for content creation and a variety of platforms for content delivery. I review the qualitative lessons learned when teaching with this material, and discuss outlook for the future. [Preview Abstract] |
(Author Not Attending)
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KP1.00130: Design and Testing of an Educational Water Tunnel Srinivas Kosaraju A new water tunnel is designed and tested for educational and research purposes at Northern Arizona University. The university currently owns an educational wind tunnel with a test section of 12in X 12in X 24in. However, due to limited size of test section and range of Reynolds numbers, its application is currently limited to very few experiments. In an effort to expand the educational and research capabilities, a student team is tasked to design, build and test a water tunnel as a Capstone Senior Design project. The water tunnel is designed to have a test section of 8in X 8in X 36in. and be able to test up to Re $=$ 50E3. Multiple numerical models are used to optimize the flow field inside the test section before building the physical apparatus. The water tunnel is designed to accommodate multiple experiments for drag and lift studies. The built-in die system can deliver up to three different colors to study the streamlines and vortex shedding from the surfaces. During the first phase, a low discharge pump is used to achieve Re $=$ 4E3 to test laminar flows. In the second phase, a high discharge pump will be used to achieve targeted Re $=$ 50E3 to study turbulent flows. [Preview Abstract] |
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KP1.00131: Girls Talk Math - Engaging Girls Through Math Media Francesca Bernardi, Katrina Morgan “Girls Talk Math: Engaging Girls through Math Media” is a free two-week long summer day camp for high-school girls in the Triangle area of NC. This past June the camp had its second run thanks to renewed funding from the Mathematical Association of America Tensor Women and Mathematics Grant. The camp involved 35 local high-school students who identify as female. Campers complete challenging problem sets and research the life of a female scientist who worked on similar problems. They report their work in a blog post and record a podcast about the scientist they researched. The curriculum has been developed by Mathematics graduate students at UNC from an inquiry based learning perspective; problem sets topics include some theoretical mathematics, but also more applied physics-based material. Campers worked on fluid dynamics, special relativity, and quantum mechanics problem sets which included experiments. The camp has received positive feedback from the local community and the second run saw a large increase in the number of participants. The program is evaluated using pre and post surveys, which measure campers' confidence and interest in pursuing higher level courses in STEM. The results from the past two summers have been encouraging. [Preview Abstract] |
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KP1.00132: Teaching fluid mechanics to high schoolers: methods, challenges, and outcome Harishankar Manikantan This talk will summarize the goals, methods, and both short- and long-term feedback from two high-school-level courses in fluid mechanics involving 43 students and cumulatively spanning over 100 hours of instruction. The goals of these courses were twofold: (a) to spark an interest in science and engineering and attract a more diverse demographic into college-level STEM programs; and (b) to train students in a `college-like' method of approaching the physics of common phenomena, with fluid mechanics as the context. The methods of instruction included classes revolving around the idea of dispelling misconceptions, group activities, `challenge' rounds and mock design projects to use fluid mechanics phenomena to achieve a specified goal, and simple hands-on experiments. The feedback during instruction was overwhelmingly positive, particularly in terms of a changing and favorable attitude towards math and engineering. Long after the program, a visible impact lies in a diverse group of students acknowledging that the course had a positive effect in their decision to choose an engineering or science major in a four-year college. [Preview Abstract] |
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KP1.00133: Eddy kinetic energy transport in barotropic turbulence Ian Grooms Eddy energy transport in rotating, barotropic turbulence is investigated using numerical simulation. Stochastic forcing is used to generate an inhomogeneous field of turbulence, and the time-mean energy profile is diagnosed. An advective-diffusive model for the transport is fit to the simulation data by requiring the model to accurately predict the observed time-mean energy distribution. Isotropic harmonic diffusion of energy is found to be an accurate model in the case of uniform, solid-body background rotation (the $f$-plane), with a diffusivity that scales reasonably well with a mixing-length law $\kappa\propto V\ell$ where $V$ and $\ell$ are `characteristic' eddy velocity and length scales. Passive tracer dynamics are added, and it is found that the energy diffusivity is $75\%$ of the tracer diffusivity. The addition of a differential background rotation with constant vorticity gradient $\beta$ leads to significant changes to the energy transport. The eddies generate and interact with a mean flow. Mean advection plus anisotropic diffusion is moderately accurate only for flows with scale separation between mean and eddies. [Preview Abstract] |
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KP1.00134: The spiral turbulence: a secondary instability of the IPS vortices in the Taylor-Couette flow? Arnaud Prigent, Talioua Abdessamad, Mutabazi Innocent We are interested in the study of the transition to turbulence in the Taylor-Couette flow, the flow between two independently rotating coaxial cylinders. Once the geometry is fixed, the flow is controlled by the inner and outer Reynolds numbers, Rei and Reo, and presents a large variety of flow regimes as described by Coles and Andereck et al. In counter-rotation, the transition is characterized by a succession of flow regimes with laminar-turbulent coexistence as the spiral turbulence, the helical alternance of laminar and turbulent flow. While they were expected to be observed before the apparition of the laminar-turbulent coexistence regimes, like the spiral turbulence, interpenetrating spiral vortices are observed before and also within these regimes. They affect significantly the flow. They are located between the inner cylinder and the nodal surface and disappear where turbulence occurs. We believe that these vortices act like finite amplitude perturbations triggering the turbulent domains in a bursting process like the one proposed by Marcus. We experimentally study the role played by these vortices through visualizations of the flow and PIV measurements. [Preview Abstract] |
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KP1.00135: Measuring Energy Dissipation in Reflecting Internal Waves using PIV Data Vrinda Desai, Bruce Rodenborn We previously conducted experiments and simulations that tested weakly nonlinear theories (Rodenborn et. al., Phys. Fluids, 2011) of internal wave reflection from a sloping boundary. In the previous study, we used integrated kinetic energy as a measure of internal wave beam energy. However, we use an algorithm by Lee et al. (Phys. Fluids, 26, 2014) to determine the energy flux of internal waves in our experiments using velocity field (PIV) measurements. We find good agreement between our laboratory data and our numerical simulations, where the energy flux is determined from the velocity and pressure fields. We also calculate the rate at which energy is dissipated in the reflection process by finding the energy flux into and out of a surface above the reflection region Eout=Ein. We find high rates of energy dissipation O(90\%) near the critical angle in both experiments and simulations. High dissipation at the critical angle occurs in our simulations even for weakly nonlinear wave beams and when the viscosity reduced by an order of magnitude, which implies that dissipation may be relevant to internal wave reflection in the ocean. [Preview Abstract] |
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