Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session KP2: Student Poster Session |
Hide Abstracts |
Room: Exhibit Hall D (Student Poster Display Area) |
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KP2.00001: FLUID DYNAMICS STUDENT POSTER COMPETITION - GENERAL FLUID DYNAMICS |
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KP2.00002: Large-eddy simulation of zero-pressure-gradient turbulent boundary layer with solid particle suspension Mustafa Rahman, Ravi Samtaney We present results of solid particles suspension and transport in a fully-developed turbulent boundary layer flow using large-eddy simulation of the incompressible Navier-Stokes equations. We adopt the Eulerian-Eulerian approach to simulating particle laden flow with a large number of particles, in which the particles are characterized by statistical descriptors. For the particulate phase, the direct quadrature method of moments (DQMOM) is chosen in which the weights and abscissas of the quadrature approximation are tracked directly rather than the moments themselves. The underlying approach in modeling the turbulence of fluid phase utilizes the stretched spiral vortex subgrid-scale model and a virtual wall model similar to the work proposed by Inoue \& Pullin (J. Fluid Mech. 2011). The solver is verified against simple analytical solutions and the computational results are found to be in a good agreement with these. The capability of the new numerical solver will be exercised to investigate turbulent transport of sand in sandstorms. Finally, the adequacy and limitations of the solver will be discussed. [Preview Abstract] |
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KP2.00003: Physical modeling of the atmospheric boundary layer for wind energy and wind engineering studies Gregory Taylor-Power, John Turner, Martin Wosnik The Flow Physics Facility (FPF) at UNH has test section dimensions W6.0m, H2.7m, L=72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPF’s ability to experimentally simulate different types of the atmospheric boundary layer (ABL): the stable, unstable, and neutral ABL. The neutral ABL is characterized by a zero potential temperature gradient, which is readily achieved in the FPF by operating when air and floor temperatures are close to equal. The stable and unstable ABLs have positive and negative vertical temperature gradients, respectively, which are more difficult to simulate without direct control of air or test section floor temperature. The test section floor is a 10 inch thick concrete cement slab and has significant thermal mass. When combined with the diurnal temperature variation of the ambient air, it is possible to achieve vertical temperature gradients in the test section, and produce weakly stable or weakly unstable boundary layer. Achievable Richardson numbers and Obukhov lengths are estimated. The different boundary layer profiles were measured, and compared to theoretical atmospheric models. [Preview Abstract] |
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KP2.00004: Rayleigh-B\'enard convection at high Prandtl numbers in circular and square geometry Stephen R. Johnston, Enrico Fonda, Katepalli R. Sreenivasan, Devesh Ranjan Experiments using water and simulations have shown that flow structures and turbulent fluctuations in Rayleigh-B\'enard convection are affected by the shape of the container. We study the effect of the geometry in both square and cylindrical test cells of aspect ratio of order unity in high Prandtl fluids (up to $10^4$). Flow visualization using a photochromic dye seeded throughout the fluid allows us to uninvasively study the evolution of the large scale structures. We discuss the observations in the two geometries and compare them with previous observations at low Prandtl numbers. [Preview Abstract] |
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KP2.00005: The Negligible Role of Thermal Inertia in the Marangoni Instability and Evaporation Instability Problems John Shrefler, Georg Dietze, Ranga Narayanan The classical Marangoni instability problem, principally introduced by Pearson in 1958, takes the interface of two fluids heated from below to be non-deflecting and as a consequence of this assumption thermal inertia is responsible for the onset of convective flows. However, in practical problems where interfacial deflections are uncontrollable and necessarily present, we find that thermal inertia is of very little importance for a broad class of fluids. Neglecting the contribution of thermal inertia, we find that the instability persists as in the classical case. This is shown by way of an integral boundary layer method for long wavelength flows and confirmed by detailed calculations using the full equations. We aim to demonstrate that the principal result that thermal inertia is unimportant continues to hold for the evaporation instability problem, provided pure component phase change is considered. [Preview Abstract] |
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KP2.00006: First Signs of Flow Reversal Within a Separated Turbulent Boundary Layer Jared Hammerton, Amy Lang A shark's skin is covered in millions of microscopic scales that have been shown to be able to bristle in a reversing flow. ~The motive of this project is to further explore a potential bio-inspired passive separation control mechanism which can reduce drag. ~To better understand this mechanism, a more complete understanding of flow reversal within the turbulent boundary layer is required. ~In order to capture this phenomenon, water tunnel testing at The University of Alabama was conducted. ~Using a long flat plate and a rotating cylinder, a large turbulent boundary layer and adverse pressure gradient were generated. ~Under our testing conditions the boundary layer had a Reynolds number of 200,000 and a boundary layer height in the testing window of 5.6 cm. ~The adverse pressure gradient causes the viscous length scale to increase and thus increase the size of the individual components of the turbulent boundary layer. ~This will make the low speed streaks approximately 1 cm in width and thus large enough to measure. ~Results will be presented that test our hypothesis that the first signs of flow reversal will occur within the section of lowest momentum located furthest from the wall, or within the low speed streaks. ~ [Preview Abstract] |
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KP2.00007: ABSTRACT WITHDRAWN |
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KP2.00008: Application of Piezoelectrics to Flapping-Wing MAVs Alex Widstrand, J. Paul Hubner Micro air vehicles (MAVs) are a class of unmanned aerial vehicles that are size-restricted and operate at low velocities and low Reynolds numbers. An ongoing challenge with MAVs is that their flight-related operations are highly constrained by their size and weight, which limits battery size and, therefore, available power. One type of MAV called an ornithopter flies using flapping wings to create both lift and thrust, much like birds and insects do. Further bio-inspiration from bats led to the design of membrane wings for these vehicles, which provide aerodynamic benefits through passive vibration. In an attempt to capitalize on this vibration, a piezoelectric film, which generates a voltage when stressed, was investigated as the wing surface. Two wing planforms with constant area were designed and fabricated. The goal was to measure the wings' flight characteristics and output energy in freestream conditions. Complications with the flapper arose which prevented wind tunnel tests from being performed; however, energy data was obtained from table-top shaker tests. Preliminary results indicate that wing shape affects the magnitude of the charge generated, with a quarter-elliptic planform outperforming a rectangular planform. [Preview Abstract] |
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KP2.00009: Ultra-high speed measurement of a laser-induced underwater shock wave Keisuke Hayasaka, Yoshiyuki Tagawa We find that a laser-induced underwater shock wave has an interesting character: peak pressure varies in propagation direction while pressure impulse is the same for all directions. In general, a shock wave is often approximated as a single-spherical wave, which seems to contradict with the aforementioned character. In this research, we investigate a structure of a laser-induced underwater shock wave in order to rationalize the character. We utilize an ultra-high speed camera to visualize the shock waves and plasmas. Our measurement results reveal that the shock wave and the plasma consist of multiple spherical-shock waves and multiple plasmas. We here suggest a simple model of multiple-shock waves: a laser-induced shock wave can be interpreted as a collection of spherical shocks originated from multiple plasmas. This model explains both the different peak pressures and the same pressure impulses. In addition, we estimate shock pressure in a two-dimensioned field using non-invasive optical methods, which measure a projected density field of a shock wave. [Preview Abstract] |
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KP2.00010: Three-dimensional blade coating of complex fluid Vachitar Singh, Emma Grimaldi, Alban Sauret, Emilie Dressaire The application of a layer of non-newtonian fluid on a solid substrate is an important industrial problem involved in polymer or paint coatings, and an everyday life challenge when it comes to spreading peanut butter on a toast. Most experimental and theoretical work has focused on the two-dimensional situation, i.e. the scraping of a fixed blade on a moving substrate to turn a thick layer of liquid into a thin coat. However the spreading of a finite volume of non-newtonian fluid using a blade has received less attention, despite significant practical and fundamental implications. In this study, we investigate experimentally the spreading of a finite volume of a model non-newtonian fluid, carbopol, initially deposited against the fixed blade. As the substrate is translated at constant speed, we characterize the dynamics of spreading and the final shape of the coated layer. We measure and rationalize the influence of the liquid volume, the height and orientation of the blade, and the speed of the substrate on the spreading. [Preview Abstract] |
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KP2.00011: FLUID DYNAMICS STUDENT POSTER COMPETITION - CFD |
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KP2.00012: ABSTRACT WITHDRAWN |
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KP2.00013: Design of a rapid magnetic microfluidic mixer Matthew Ballard, Drew Owen, Zachary Grant Mills, Srinivas Hanasoge, Peter Hesketh, Alexander Alexeev Using three-dimensional simulations and experiments, we demonstrate rapid mixing of fluid streams in a microchannel using orbiting magnetic microbeads. We use a lattice Boltzmann model coupled to a Brownian dynamics model to perform numerical simulations that study in depth the effect of system parameters such as channel configuration and fluid and bead velocities. We use our findings to aid the design of an experimental micromixer. Using this experimental device, we demonstrate rapid microfluidic mixing over a compact channel length, and validate our numerical simulation results. Finally, we use numerical simulations to study the physical mechanisms leading to microfluidic mixing in our system. Our findings demonstrate a promising method of rapid microfluidic mixing over a short distance, with applications in lab-on-a-chip sample testing. [Preview Abstract] |
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KP2.00014: Controlling Hazardous Releases while Protecting Passengers in Civil Infrastructure Systems Sara P. Rimer, Nikolaos D. Katopodes The threat of accidental or deliberate toxic chemicals released into public spaces is a significant concern to public safety, and the real-time detection and mitigation of such hazardous contaminants has the potential to minimize harm and save lives. Furthermore, the safe evacuation of occupants during such a catastrophe is of utmost importance. This research develops a comprehensive means to address such scenarios, through both the sensing and control of contaminants, and the modeling of and potential communication to occupants as they evacuate. A computational fluid dynamics model is developed of a simplified public space characterized by a long conduit (e.g. airport terminal) with unidirectional ambient flow that is capable of detecting and mitigating the hazardous contaminant (via boundary ports) over several time horizons using model predictive control optimization. Additionally, a physical prototype is built to test the real-time feasibility of this computational flow control model. The prototype is a blower wind-tunnel with an elongated test section with the capability of sensing (via digital camera) an injected `contaminant' (propylene glycol smoke), and then mitigating that contaminant using actuators (compressed air operated vacuum nozzles) which are operated by a set of pressure regulators and a programmable controller. Finally, an agent-based model is developed to simulate ``agents'' (i.e. building occupants) as they evacuate a public space, and is coupled with the computational flow control model such that agents must interact with a dynamic, threatening environment. [Preview Abstract] |
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KP2.00015: Modifying Airfoils for Low Reynolds Flight Christopher Ong, Maria-Isabel Carnasciali There has been increased interest in Micro Air Vehicles (MAV) by both the private and government sectors. MAVs are miniature classed-UAVs that can operate in tighter spaces in urban or wooded regions.~ Sizes vary -- from that of an insect to that of small bird -- depending on intended functionality and usually operate at much lower speeds. Studies have shown that the aerodynamic performance of well-known airfoils can change significantly at low Reynolds numbers. In this work, we examine via parametric CFD analysis tools the behavior of airfoils at low Reynolds values. Furthermore, we investigate the impact of adding bio-inspired features to the airfoils such as humps or dimples. Results will be presented in comparison to established values. [Preview Abstract] |
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KP2.00016: Controlling Wavebreaking in a Viscous Fluid Conduit Dalton Anderson, Michelle Maiden, Mark Hoefer This poster will present a new technique in the experimental investigation of dispersive hydrodynamics. In shallow water flows, internal ocean waves, superfluids, and optical media, wave breaking can be resolved by a dispersive shock wave (DSW). In this work, an experimental method to control the location of DSW formation (gradient catastrophe) is explained. The central idea is to convert an initial value problem (Riemann problem) into an equivalent boundary value problem. The system to which this technique is applied is a fluid conduit resulting from high viscosity contrast between a buoyant interior and heavier exterior fluid. The conduit cross-sectional area is modeled by a nonlinear, conservative, dispersive, third order partial differential equation. Using this model, the aim is to predict the breaking location of a DSW by controlling one boundary condition. An analytical expression for this boundary condition is derived by solving the dispersionless equation backward in time from the desired step via the method of characteristics. This is used in experiment to generate an injection rate profile for a high precision piston pump. This translates to the desired conduit shape. Varying the jump height and desired breaking location indicates good control of DSW formation. This result can be improved by deriving a conduit profile by numerical simulation of the full model equation. Controlling the breaking location of a DSW allows for the investigation of dynamics independent of the boundary. [Preview Abstract] |
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KP2.00017: Modeling Droplet Motion on Liquid-Infused Surface Using Lattice Boltzmann Method Mingfei Zhao, Xin Yong Understanding self-assembly of nanoparticles driven by the evaporation of the particle-covered sacrificial liquid mass dispensed on a solid substrate is of technological important for various printing and deposition techniques. Although the convective deposition of suspended nanoparticles (known as the coffee ring effect) has been studied extensively, the self-assembly of nanoparticles directly delivered to the liquid-gas interface remains unexplored. In this work, we develop a hybrid model that combines free-energy multiphase LBM with Lagrangian particle tracking method to reveal the complex interplay between nanoparticles, convective flow in liquid, and the dynamics of three-phase contact line on the substrate. We first verify our computational model using existing computational and experimental results. We then investigate the evaporation phenomena of a particle-covered droplet with specified nanoparticle distributions and wetting properties. By controlling the boundary conditions, we can implement desired contact angle hysteresis on the substrate that matches experiment observations. This study provides a theoretical framework to explore the dynamics of nanoparticle self-assembly at evaporating liquid-vapor interfaces. [Preview Abstract] |
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KP2.00018: A finite volume method for fluctuating hydrodynamics of simple fluids Kiran Narayanan, Ravi Samtaney, Brian Moran Fluctuating hydrodynamics accounts for stochastic effects that arise at mesoscopic and macroscopic scales. We present a finite volume method for numerical solutions of the fluctuating compressible Navier Stokes equations. Case studies for simple fluids are demonstrated via the use of two different equations of state (EOS) : a perfect gas EOS, and a Lennard-Jones EOS for liquid argon developed by Johnson {\it et al. } (Mol. Phys. 1993). We extend the fourth order conservative finite volume scheme originally developed by McCorquodale and Colella (Comm. in App. Math. \& Comput. Sci. 2011), to evaluate the deterministic and stochastic fluxes. The expressions for the cell-centered discretizations of the stochastic shear stress and stochastic heat flux are adopted from Espanol, P (Physica A. 1998), where the discretizations were shown to satisfy the fluctuation-dissipation theorem. A third order Runge-Kutta scheme with weights proposed by Delong et. al. (Phy. Rev. E. 2013) is used for the numerical time integration. Accuracy of the proposed scheme will be demonstrated. Comparisons of the numerical solution against theory for a perfect gas as well as liquid argon will be presented. Regularizations of the stochastic fluxes in the limit of zero mesh sizes will be discussed. [Preview Abstract] |
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KP2.00019: FLUID DYNAMICS STUDENT POSTER COMPETITION - MICROFLOWS, DROPLETS AND BUBBLES |
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KP2.00020: Modeling a Bouncing Droplet with a Lubrication Force Matthew Cessna In our laboratory experiments, a shallow bath of silicone oil of a particular viscosity was placed on an electromagnetic shaker where it was driven by a constant frequency just below the threshold of Faraday instability. A small droplet was then manually created on the surface of the vibrating bath and the bouncing behavior of the droplet was observed and recorded with the aid of a high speed camera. Droplets of sufficient size do not coalesce with the bath due to a thin air film that forms between them. Coalescence is avoided when the time for the bath to accelerate the droplet back into ballistic motion is shorter than the time required for the thin air film to deplete. Computer software was utilized to process the images and plot the dynamics of the droplet. The experimental data revealed that the acceleration of the droplets measured below -1 g at the moment when a droplet was being launched back into flight by the oscillating bath. We investigate whether lubrication theory accounts for these measurements and model a bouncing droplet on a vibrating bath of the same viscosity with a lubrication force to reproduce our experimental data using Matlab. [Preview Abstract] |
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KP2.00021: Partial Coalescence of Liquid Cones with an Electrified Plate Madeline Zhang, Casey Bartlett, James Bird As a liquid drop contacts a surface in the presence of an electric field, charge can promote rapid spreading upon contact. In the moments prior to contact, the drop will often develop a conical tip that is qualitatively similar to that seen in droplet pairs undergoing electrocoalescence. Recently it has been shown that in strong electric fields, droplet pairs can contact and then immediately recoil. Yet, it is unclear whether a similar phenomenon exists for droplets that contact charged solid surfaces. Here, we show that droplets can indeed be repelled from dry rigid surfaces, provided that there is sufficient charge. Our high-speed experiments reveal that when an electric field deforms the contacting drop beyond a critical cone angle, the drop will recoil rather than spread. This critical angle is significantly greater than the critical angle previously observed for the identical drop pair coalescence-recoil transition, but is consistent with surface tension-driven dynamics. [Preview Abstract] |
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KP2.00022: Experimental study on the motion of a pair of bubbles in quiescent liquids Hiroaki Kusuno, Toshiyuki Sanada Understanding of the bubble-bubble interaction problem is important step to achieve more accurate bubbly flow simulation. Some theoretical models of bubble-bubble interaction have been proposed. And some numerical results have also been reported. However, the experimental verifications are insufficient. In this study, we experimentally investigated the motion of a pair of bubbles initially positioned in-line configuration in ultrapure water or an aqueous surfactant solution. The bubble motion were observed by two high speed video cameras. The bubbles Reynolds number was ranged from 50 to 300. In ultrapure water, initially the trailing bubble deviated from the vertical line on the leading bubble owing to the wake of the leading bubble. And then, the slight difference of the bubble radius changed the relative motion. When the trailing bubble slightly larger than the leading bubble, the trailing bubble approached to the leading bubble due to it's buoyancy difference. The bubbles attracted and collided only when the bubbles rising approximately side by side configuration. In addition, we will also discuss the motion of bubbles rising in an aqueous surfactant solution. [Preview Abstract] |
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KP2.00023: Polymer and protein interfacial competition in a shell production process Emma Willard, Greg Randall We are exploring oil-in-aqueous polymer compound droplet formulations to UV polymerize into shells while in a strong AC electric field (kV/cm, 20 MHz). The electric field drives the drops to adopt a concentric configuration so that a ``perfect'' spherical shell can be polymerized with a uniform wall thickness. In our previous study of oil-in-water droplet centering, we determined that droplet stretching in the electric field was a problem, which we overcame by using protein additives to strengthen the oil/water interface. However, adding polymer to the shell fluid has been shown to weaken the droplet interface and further complicates T junction droplet generation. In this work, we study the adsorption competition between bovine serum albumin and polyethylene glycol diacrylate with the pendant drop method to generate a polymer/protein shell formulation that will resist stretching in the centering electric field. Furthermore, we explore droplet generation of polymer/protein shell formulations in a double T junction and stretching in an electric field. [Preview Abstract] |
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KP2.00024: A new device for generating thin jets of highly-viscous liquid Hajime Onuki, Yuto OI, Yoshiyuki Tagawa Thin liquid jets are applied to various devices, such as ink-jet printers. However, it is challenging to generate liquid jets of highly-viscous liquids ($\sim$ 1,000 cSt) using existing methods. To overcome this challenge, we invent a highly-viscous liquid-jet generator. This device has simple structure as follows: a wettable-thin tube is inserted into a liquid filled container. We keep the liquid level inside a thin tube deeper than that outside of the tube. When an impulsive force acts on the bottom of the container, a thin jet is generated. The jet is up to 20 times faster than the initial velocity given by the impulsive force. We successfully generate jets with a wide range of viscosity (1-1,000 cSt). We also propose the physical model based on pressure-impulse approach to rationalize its mechanism. Inside the thin tube, a gradient of pressure impulse is much larger than that outside of the tube. We verify the performance of our device experimentally. We find that the proposed model can describe all experimental results in this research. [Preview Abstract] |
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KP2.00025: Modeling Electrospray Deposition of Nanoparticle Inks Ao Li, Jefferson Fideles Da Silva, Xin Yong Electrospray of nanoparticle inks is of great importance to the manufacturing of functional materials. In this study, we develop a new three-dimensional multiphysics method to model the electrospray of colloidal suspension to a flat substrate. The Lagrangian Particle Tracking (LPT) transport equation is coupled to mass and heat transfer using convective droplet vaporization model, which allow us to track each particle-laden ink droplets and dry nanoparticles in the electrospray plume and probe the deposit structures. Herein, we consider dilute inks that are experimentally relevant, assuming monodisperse nanoparticles. We characterize the overall statistics of the plume and the dynamics of individual ink droplet or dry nanoparticle. It is shown that the segregation effect affects not only primary and satellite droplets but also dry nanoparticles. We observe nanoparticles deposit structure changing process, in particular time evolution of the density profile along radial direction. Our results show that the region of high nanoparticle density transitioning from only the edge to both the edge and center, which agrees with previous experimental studies. [Preview Abstract] |
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KP2.00026: Experimental Research on the Capture of Fine Particles in a High-voltage Electric Field Xing Jin, Shuiqing Li Mechanisms for capturing of fine particles through a high-voltage electric field were examined using the electrostatic precipitator (ESP) as an example system. The dimensionless equations governing particle transport were solved and a laboratory-scale ESP was experimentally examined. The analysis indicates that particles in the size range of 0.1-1$\mu $m have the lowest electric migration velocity and there is a capture-effective zone in the middle of the ESP for fine particles. Subsequent increase in length had little effect for grade efficiency because of the influence of electrohydrodynamic (EHD) flow. In the particle boundary layer zone, dipole-dipole force and VDW force play crucial roles in capturing fine particles. The packing structure of fine particles on the collecting plate is investigated by digital microscopy technology. The effects of pre-charging, pre-polarization and external electric field on packing morphologies are discussed. It is found that the dipole-dipole force between particles causes the formation of long particle chains and the maximum length of particle dendrites during the packing is dependent on both the density of external field and deposit structure. [Preview Abstract] |
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KP2.00027: Volume of a laser-induced microjet Sennosuke Kawamoto, Keisuke Hayasaka, Yuto Noguchi, Yoshiyuki Tagawa Needle-free injection systems are of great importance for medical treatments. In spite of their great potential, these systems are not commonly used. One of the common problems is strong pain caused by diffusion shape of the jet. To solve this problem, the usage of a high-speed highly-focused microjet as needle-free injection system is expected. It is thus crucial to control important indicators such as ejected volume of the jet for its safe application. We conduct experiments to reveal which parameter influences mostly the ejected volume. In the experiments, we use a glass tube of an inner diameter of 500 micro-meter, which is filled with the liquid. One end is connected to a syringe and the other end is opened. Radiating the pulse laser instantaneously vapors the liquid, followed by the generation of a shockwave. We find that the maximum volume of a laser-induced bubble is approximately proportional to the ejected volume. It is also found that the occurrence of cavitation does not affect the ejected volume while it changes the jet velocity. [Preview Abstract] |
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KP2.00028: FLUID DYNAMICS STUDENT POSTER COMPETITION - BIOFLUIDS |
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KP2.00029: A Modification of the Levich Model to Flux at a Rotating Disk in the presence of Planktonic Bacteria Akhenaton-Andrew Jones, Cullen Buie The Levich model of flow at a rotating disk describes convective mass transport to a disk when edge effects and wall effects can be neglected. It is used to interpret electrochemical reaction kinetics and electrochemical impedance of flow systems. The solution has been shown to be invalid for high densities ($\sim 1\% $v/v) of inert, non-motile nano-sized particles (\textless 0.1 $\mu $m) and macro-particles (\textgreater 1.5 $\mu $m), yet little work has been done for motile bacteria and bacterial sized particles. The influence of planktonic bacteria on rotating disk experiments is crucial for the evaluation of electrochemically active biofilms. In this work, we show that the presence of bacteria creates significant deviation from the ideal Levich model not shared by inert particles. We also study the impact of dead (fixed) bacteria on deviation form the Levich model. This work has implications for studies of microbial induced corrosion, microbial adhesion, and antibiotic transport to adhered biofilms preformed in rotating disk systems. [Preview Abstract] |
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KP2.00030: Intraventricular flow alterations due to dyssynchronous wall motion Audrey M. Pope, Hong Kuan Lai, Milad Samaee, Arvind Santhanakrishnan Roughly 30{\%} of patients with systolic heart failure suffer from left ventricular dyssynchrony (LVD), in which mechanical discoordination of the ventricle walls leads to poor hemodynamics and suboptimal cardiac function. There is currently no clear mechanistic understanding of how abnormalities in septal-lateral (SL) wall motion affects left ventricle (LV) function, which is needed to improve the treatment of LVD using cardiac resynchronization therapy. We use an experimental flow phantom with an LV physical model to study mechanistic effects of SL wall motion delay on LV function. To simulate mechanical LVD, two rigid shafts were coupled to two segments (apical and mid sections) along the septal wall of the LV model. Flow through the LV model was driven using a piston pump, and stepper motors coupled to the above shafts were used to locally perturb the septal wall segments relative to the pump motion. 2D PIV was used to examine the intraventricular flow through the LV physical model. Alterations to SL delay results in a reduction in the kinetic energy (KE) of the flow field compared to synchronous SL motion. The effect of varying SL motion delay from 0{\%} (synchronous) to 100{\%} (out-of-phase) on KE and viscous dissipation will be presented. [Preview Abstract] |
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KP2.00031: Diastolic filling in a physical model of obstructive hypertrophic cardiomyopathy Joseph Schovanec, Milad Samaee, Hong Kuan Lai, Arvind Santhanakrishnan Hypertrophic Cardiomyopathy (HCM) is an inherited heart disease that affects as much as one in 500 individuals, and is the most common cause of sudden death in young athletes. The myocardium becomes abnormally thick in HCM and deforms the internal geometry of the left ventricle (LV). Previous studies have shown that a vortex is formed during diastolic filling, and further that the dilated LV morphology seen in systolic heart failure results in altering the filling vortex from elliptical to spherical shape. We have also previously shown that increasing LV wall stiffness decreases the filling vortex circulation. However, alterations to intraventricular filling fluid dynamics due to an obstructive LV morphology and locally elevated wall stiffness (in the hypertrophied region) have not been previously examined from a mechanistic standpoint. We conducted an experimental study using an idealized HCM physical model and compared the intraventricular flow fields obtained from 2D PIV to a baseline LV physical model with lower wall stiffness and anatomical geometry. The obstruction in the HCM model leads to earlier breakdown of the filling vortex as compared to the anatomical LV. Intraventricular filling in both models under increased heart rates will be discussed. [Preview Abstract] |
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KP2.00032: FLUID DYNAMICS STUDENT POSTER COMPETITION - COMBUSTION |
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KP2.00033: Nonlinear dynamics of flame front instability induced by radiative heat loss: period-doubling bifurcation and chaos Hikaru Kinugawa, Kazuhiro Ueda, Hiroshi Gotoda We numerically study the nonlinear dynamics of flame front instability induced by radiative heat loss on the basis of dynamical systems theory. Our previous studies have shown that the radiative heat loss significantly produces the deterministic chaos of flame front temperature fluctuations throughout the period-doubling bifurcation known as Feigenbaum scenario [Gotoda et al., Combust. Theor. Model. 14, 479-493 (2010)], while its short-term behavior can be predicted using a local and global nonlinear predictors [Gotoda et al., Chaos 22, 033106 (2012)]. The present study reports that the similar kind of bifurcation process clearly appears at the fuel concentration, and that the fuel concentration dynamics in the well-developed chaos region is much more complicated than that of the flame front temperature. Recurrence quatification analysis we adopted in the present study can quantify the significant changes in the dynamics in the chaos region that cannot be capture in the bifurcation diagram. [Preview Abstract] |
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KP2.00034: Characterization of degeneration process in thermo-acoustic combustion instability using dynamical systems theory Kenta Hayashi, Hiroshi Gotoda, Yuta Okuno, Shigeru Tachibana We have experimentally investigated the degeneration process of combustion instability in a lean premixed gas-turbine model combustor on the basis of dynamical systems theory. Our previous study reported that with increasing the equivalence ratio, the dynamical behavior of combustion state close to lean blowout transits from stochastic fluctuations to periodic thermoacoustic combustion oscillations via low-dimensional chaotic oscillations (Gotoda et al., Chaos, 21, 013124 (2011) / Gotoda et al., Chaos, 22, 043128 (2012)). The further increase in the equivalence ratio gives rise to the quasi-periodic oscillations and the subsequent chaotic oscillations with small amplitudes. The route to chaotic oscillations is quantitatively shown by the use of nonlinear time series analysis involving the color recurrence plots, permutation entropy and local predictor. [Preview Abstract] |
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KP2.00035: Stratification effects on laminar premixed-flame response to mixture perturbations Tiernan Casey, Jyh-Yuan Chen While complete mixing on the molecular level is desirable for ensuring that combustion processes are limited by chemical kinetics rather than mass transport, it is often the case that practical devices operate with some degree of unmixedness. As such, phenomena such as ignition or flame propagation will inevitably occur in regions that exhibit mixture or thermal non-uniformity. Here we present unsteady simulations of laminar premixed flames in the low-Mach limit subject to mixture perturbations of varying wavelength and amplitude, and qualify their effect on the flame behavior. When flames experience variations in mixture the transport processes in the flame zone vary with time and the flame behavior can depend on the burned gas history. Also, the possibility of extending flames beyond their flammability limits so as to maximize the overall mass of fuel burned is explored by exploiting these unsteady effects. [Preview Abstract] |
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KP2.00036: High-Fidelity Simulations of Electrically-Charged Atomizing Diesel-Type Jets Benoit Gaillard, Mark Owkes, Bret Van Poppel Combustion of liquid fuels accounts for over a third of the energy usage today. Improving efficiency of combustion systems is critical to meet the energy needs while limiting environmental impacts. Additionally, a shift away from traditional fossil fuels to bio-derived alternatives requires fuel injection systems that can atomize fuels with a wide range of properties. In this work, the potential benefits of electrically-charged atomization is investigated using numerical simulations. Particularly, the electrostatic forces on the hydrodynamic jet are quantified and the impact of the forces is analyzed by comparing simulations of Diesel-type jets at realistic flow conditions. The simulations are performed using a state-of-the-art numerical framework that globally conserves mass, momentum, and the electric charge density even at the gas-liquid interface where discontinuities exist. [Preview Abstract] |
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