Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session LA: Poster Session (3:15-5:00PM) |
Hide Abstracts |
Room: Ballroom I-IV Foyer |
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LA.00001: Oscillatory Behavior of an Arc Airfoil in Low-Speed Airflow Majid Molki, Negin Sattari A computational investigation is conducted to study the oscillatory behavior of an arc airfoil situated in low-speed airflow. The present work is relevant to situations where the conventional rigid airfoils do not apply, such as the flight of bats. The outcome of this study is also beneficial in the design of micro air vehicles with flexible wings. The computations are performed using a deforming mesh to accommodate the airfoil oscillations. An unsteady, spatially second-order algorithm is employed to capture the time-variations of the lift and drag coefficients. A key feature of the present work is the flow response to airfoil oscillations. Fast Fourier Transform was applied to various parameters of the flow. For certain values of angle of attack for the non-oscillating airfoil, the flow has a dominant frequency and a well-defined vortex shedding. For other values of angle of attack, the flow around the non-oscillating airfoil contains many frequencies and has complex vortical structures. However, the oscillating airfoil in all cases makes the flow field periodic with well-defined patterns of vortex shedding. In this work, the flux of vorticity from the airfoil surface into the airflow is computed and compared with the pressure gradient along the surface of the airfoil. Effects of oscillations on magnitude and behavior of aerodynamic forces are also studied. [Preview Abstract] |
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LA.00002: A universal law of the elasticity of multilamellar lipid membranes under compression Yves Dubief, Leonie Cowley Multilamellar lipid membranes play critical roles in the mechanics and chemistry of cells, lung and biolubrication of articular joints. One of their most interesting mechanical properties is their elasticity than enable them to resist anisotropic compression where the pressure in the direction normal to the membrane is larger than in other directions. This resistance to compression is strongly dependent on hydration, or the number of water molecules confined between two adjacent lipid membranes. Using coarse-grained molecular dynamics, we show that the elastic behavior or multilamellar membranes is in fact universal over a large range of hydration. A universal law is derived from considerations of intermolecular forces and volume vacancy between lipid molecules. The ability of the proposed law to predict the increase of the membrane surface area as a function of the compression rate and hydration is expected to help the modeling of multilamellar membranes at the continuum level. [Preview Abstract] |
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LA.00003: Designing self-propelling micro-swimmers using responsive gels Benjamin Bingham, Hassan Masoud, Alexander Alexeev We use computational modeling to design a synthetic micro-swimmer that not only self-propels but also navigates in highly viscous environments. Our simple swimmer consists of a cubic gel body with two rectangular stiff flaps attached to its opposite sides and a stimuli-sensitive flexible flap at the body front. The responsive gel undergoes periodic expansion and contraction that can be induced by certain external stimuli such as temperature, light, magnetic or electric fields. The periodic changes in the volume of the body lead to asymmetric beating motion of the propulsion flaps which propel the micro-swimmer through the inertialess fluid. We study the effect of body elasticity on the locomotion of our swimmer and show how the elasticity of the body can be harnessed to induce forward and backward swimming motion. We also demonstrate that our swimmer can successfully turn in the desired direction following the bending of the responsive steering flap. In this scenario, the steering flap bends and creates flow asymmetry which results in the swimmer rotation. [Preview Abstract] |
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LA.00004: Flexible Wing Pitch-up and Pitch-down in Free Steam Flows D. Qi, G. He, Y. Liu The direct simulations of the pitch-up and pitch-down of flexible and rigid wings in a free stream are conducted at the Reynolds number of $Re=100$ by using the lattice Boltzmann flexible particle method. The effect of bending flexibility in span-wise direction on unsteady aerodynamics are investigated. It is found that when the reduced frequency is large, the lift and drag forces increase nonlinearly upto a maximum as the flexibility increases, then falls down as the flexibility becomes excessively large. The maximum value in both lift and drag forces are significantly larger for a flexible wing than for a rigid wing. However, when the reduced frequency is small, no obvious lift maximum is observed. It seems that flexibility can be used to enhance the lift force at a high reduced frequency. The power efficiency, or lift force per input power, has a similar behavior to the lift, indicating the flexibility could benefit the power efficiency. Surprisingly flexibility improves lift only during pitch-down motion while the flexibility has a negative impact on lift during pitch-up motion, indicating that the pitch-down motion dominates the lift improvement due to flexibility. In a maneuver case a small and adequate deformation may largely enhances the wake capture, results in large LEV and TEV and reduces the flow separation. The wake capture is a main mechanism for a flexible wing to improve the lift. [Preview Abstract] |
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LA.00005: Simplified physical models of the flow around flexible insect wings at low Reynolds numbers Steve Harenberg, Johnny Reis, Laura Miller Some of the smallest insects fly at Reynolds numbers in the range of 5-100. We built a dynamically scaled physical model of a flexible insect wing and measured the resulting wing deformations and flow fields. The wing models were submerged in diluted corn syrup and rotated about the root of the wing for Reynolds numbers ranging from 1-100. Spatially resolved flow fields were obtained using particle image velocimetry (PIV). Deformations of the wing were tracked using DLTdv software to determine the motion and induced curvature of the wing. [Preview Abstract] |
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LA.00006: Particle Deposition During Airway Closure Cheng-Feng Tai, David Halpern, James B. Grotberg Inhaled aerosol particles deposit in the lung and may be from environmental, toxic, or medical therapy sources. While much research focuses on inspiratory deposition, primarily at airway bifurcations due to inertial impaction, there are other mechanisms that allow the particles to reach the airway surface, such as gravitational settling and diffusion depending on particle size. We introduce a new mechanism not previously studied, i.e. aerosol deposition from airway closure. The airways are lined with a liquid layer. Due to the surface tension driven instability, a liquid plug can form from this layer which blocks the airway. This process of airway closure tends to occur toward the end of expiration. In this study, the efficiency of the impaction of the particles during airway closure will be investigated. The particles will be released from the upstream of the airway and convected by the air flow and deposited onto the closing liquid layer. We solve the governing equations using a finite volume approach in conjunction with a sharp interface method for the interfaces. Once the velocity field of the gas flow is obtained, the path of the particles will be calculated and the efficiency of the deposition can be estimated. [Preview Abstract] |
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LA.00007: Transient motion of mucus plugs in respiratory airways Parsa Zamankhan, Yingying Hu, Brian Helenbrook, Shuichi Takayama, James B. Grotberg Airway closure occurs in lung diseases such as asthma, cystic fibrosis, or emphysema which have an excess of mucus that forms plugs. The reopening process involves displacement of mucus plugs in the airways by the airflow of respiration. Mucus is a non-Newtonian fluid with a yield stress; therefore its behavior can be approximated by a Bingham fluid constitutive equation. In this work the reopening process is approximated by simulation of a transient Bingham fluid plug in a 2D channel. The governing equations are solved by an Arbitrary Lagrangian Eulerian (ALE) finite element method through an in-house code. The constitutive equation for the Bingham fluid is implemented through a regularization method. The effects of the yield stress on the flow features and wall stresses are discussed with applications to potential injuries to the airway epithelial cells which form the wall. The minimum driving pressure for the initiation of the motion is computed and its value is related to the mucus properties and the plug shape. [Preview Abstract] |
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LA.00008: Mucus Rupture in A Collapsed airway: An Experimental Study Yingying Hu, Shiyao Bian, James B. Grotberg Mucus plugs can completely obstruct an airway. Difficulty in mucus clearance results in lost gas exchange and inflammation. Non-Newtonian properties of mucus, yielding stress and shear-thinning, play significant roles in mucus clearance. We use aqueous carbopol 940 as a mucus stimulant to study clearance of a mucus plug with properties of yielding stress and shear-thinning in a bench-top experiment. A collapsed airway of the 12$^{th}$ generation in a human lung is simulated in a two-dimensional PDMS channel. A stable pressure drop is set along the plug to drive rupture. A micro-PIV technique is used to acquire velocity fields during the rupture process. A yielding pressure drop (initiating plug yielding) is nearly independent of initial plug length. Plug rupture can occur by focused deformation along the centerline or by total plug propagation where the trailing film is thicker than the precursor film. Maximum velocity appears at the rupture moment, and increases at higher pressure drop or smaller plug length. The wall shear gradient can undergo a rapid reversal when rupture occurs, possibly an injurious event to underlying airway epithelial cells. [Preview Abstract] |
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LA.00009: Microbubble array under ultrasound excitation and its application in cell capture Jifu Tan, Antony Thomas, Yaling Liu In this paper, we studied the fluid flow and particle motion induced by a microbubble array exited under ultrasound. A circulation vortex generated in spaces between microbubble array could be controlled by the spacing of the array, the amplitude and frequency of the ultrasound. We observed that particles/cells of particular size could be trapped near the microbubble surface. The microbubble array is used to enrich bimolecular concentration locally as well as capture cells. Such active attraction mechanism has advantages over traditional passive capture methods. [Preview Abstract] |
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LA.00010: Dynamic behavior of lean swirling premixed flame generated by change in gravitational orientation -Nonlinear forecasting based on the complex network theory Masahito Amano, Koshiro Maki, Takaya Miyano, Hiroshi Gotoda We experimentally investigated the deterministic nature in the dynamic behavior of a lean swirling premixed flame generated by a change in gravitational orientation from the viewpoint of nonlinear forecasting based on the complex network theory. When the gravitational direction is changed relative to the flame front, i.e., in inverted gravity, an unstable flame is formed in a limited domain of equivalence ratio and swirl number (Gotoda. H et al., PRE, vol. 81, 026211, 2010). A radial basis function network, which quantifies the predictability of time variations in flame front fluctuations of the unstable flames, is applied as a sophisticated nonlinear forecasting method in this work. A nonlinear forecasting approach based on the complex network theory clearly demonstrates that the dynamic behavior of flame front fluctuations represents low-dimensional deterministic chaos. The deterministic nature in the dynamic behavior of flame front fluctuations revealed using the radial basis function network has not yet been reported in previous research on the flame front instability. [Preview Abstract] |
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LA.00011: Analysis and Development of a Quick Acting Diaphragm-less Shock Tube Driver Rocco Portaro, Hoi Dick Ng This work discusses the construction and performance characteristics of a diaphragmless shock tube driver. Shock waves play integral roles in many industrial, medical and scientific environments, consequently it is important to observe the behaviour of these waves and how they interact with their surroundings. The diaphragmless shock tube provides a quick and effective means of producing shock waves in gases. The major advantages compared to conventional diaphragms include, minimal downtime between repeated experiments, opening times comparable to those of conventional diaphragms and infinitely adjustable opening pressure without the use of various diaphragm thicknesses. Moreover, the diaphragmless design also eliminates fragments that are carried downstream of the shock tube once the conventional diaphragm is ruptured. The design utilized in this work is built on that of Downey et al. [M.S. Downey, T.J. Cloete, A.D.B.Yates, Shock Waves 21(4): 315-319, 2011] and is improved in order to obtain faster opening times leading to stronger shock formation. Furthermore in depth numerical analysis using the commercial CFD package Fluent is carried out to validate experimental data for driven pressures and opening times as a function of driver pressure. [Preview Abstract] |
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LA.00012: ABSTRACT WITHDRAWN |
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LA.00013: Calibration of the k-$\epsilon$ model constants for use in CFD applications Nina Glover, Serge Guillias, Liora Malki-Epshtein The k-$\epsilon$ turbulence model is a popular choice in CFD modelling due to its robust nature and the fact that it has been well validated. However it has been noted in previous research that the k-$\epsilon$ model has problems predicting flow separation as well as unconfined and transient flows. The model contains five empirical model constants whose values were found through data fitting for a wide range of flows (Launder 1972) but ad-hoc adjustments are often made to these values depending on the situation being modeled. Here we use the example of flow within a regular street canyon to perform a Bayesian calibration of the model constants against wind tunnel data. This allows us to assess the sensitivity of the CFD model to changes in these constants, find the most suitable values for the constants as well as quantifying the uncertainty related to the constants and the CFD model as a whole. [Preview Abstract] |
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LA.00014: ABSTRACT WITHDRAWN |
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LA.00015: Control of Polymer Electrodes Shape via Microflow Control in a Drying Droplet Yunseok Jang We demonstrated a simple patterning method for the deposition of polymer electrodes such as poly(3,4- ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). We made use of the difference in wettability between hydrophobic surfaces and hydrophilic surfaces to make the patterns. However, the patterns made with our patterning method created undesirable ring-like stains, which were caused by the outward flow of the solute within the PEDOT/PSS solution drop. To achieve homogenous device performance, we proposed a simple process for removing this ring-like stain by making the surface tension gradient in the PEDOT/PSS solution drop. Because this surface tension gradient causes the inward flow of the solute within the PEDOT/PSS solution drop, the ring-like stain is removed. Finally, we confirmed the potential of our patterning method for polymer electrodes such as the PEDOT/PSS by fabricating pentacene thin-film transistors (TFTs) and measuring the electrical properties of the pentacene TFTs. [Preview Abstract] |
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LA.00016: Experimental investigation of free falling thin disks. Part II: Onset of three dimensional motion from zigzag to spiral Cunbiao Lee, Hongjie Zhong The free falling motion of thin disk with small dimensionless moment of inertia was investigated experimentally. Transition from two dimensional zigzag motions to three dimensional spiral motions takes place as a consequence of breakup of planar symmetry flow structures. The counter-rotating vortices behind the disk became asymmetry induced by the instability of three dimensional disturbances, one of the separation location moves from the edge to the disk broad surface which induced a new upright vortex. The oscillation in the direction normal to zigzag plane increases with the development of instability. Meanwhile, the oscillation of nutation angle vanishes and reaches a constant value. In addition, we have shown that small moment of inertia is responsible for growth of disturbances in the third dimension by means of generalized Kirchhoff equations. [Preview Abstract] |
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LA.00017: Experimental study on thermocapillary motion of isolated drop and coalescence problems of drops JingChang Xie, Hai Lin Thermocapillay migrations of drops under temperature gradient were studied through ground-based experiment, experiment using drop tower and space experiment in microgravity. The motion of isolated drop at moderate to large Marangoni numbers (Ma) and the interaction of drops were investigated. Experimental data show that the scaled migration velocity of isolated drop, V/V$_{YGB}$, appears an obvious decrease trend with the increase of Maragoni number up to 5500. This result does not agree with some theoretical predictions. Interferometry was applied in our space experiment to visualize the whole temperature field and to get detailed informations of temperature variation around a moving drop and the thermal wake behind it. Interferometric images indicate that drop's migration very sensitively follows the direction of temperature gradient because of slow migration velocity and microgravity condition. The temperature disturbance around a leading drop and the thermal wake behind it would exist for a quite long time in the real case. The variation of temperature field would substantially affect the migration velocity of a trailing drop in both direction and value, and this would bring about coalescence problems of two or multiple drops. [Preview Abstract] |
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LA.00018: Droplet Breakup Mechanisms in Air-blast Atomizers Amir Abbas Aliabadi, Seyed Mohammad Taghavi, Kelly Lim Atomization processes are encountered in many natural and man-made phenomena. Examples are pollen release by plants, human cough or sneeze, engine fuel injectors, spray paint and many more. The physics governing the atomization of liquids is important in understanding and utilizing atomization processes in both natural and industrial processes. We have observed the governing physics of droplet breakup in an air-blast water atomizer using a high magnification, high speed, and high resolution LASER imaging technique. The droplet breakup mechanisms are investigated in three major categories. First, the liquid drops are flattened to form an oblate ellipsoid (lenticular deformation). Subsequent deformation depends on the magnitude of the internal forces relative to external forces. The ellipsoid is converted into a torus that becomes stretched and disintegrates into smaller drops. Second, the drops become elongated to form a long cylindrical thread or ligament that break up into smaller drops (Cigar-shaped deformation). Third, local deformation on the drop surface creates bulges and protuberances that eventually detach themselves from the parent drop to form smaller drops. [Preview Abstract] |
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LA.00019: Development of Anodized-Aluminum Temperature-Sensitive Paint for Flow Field Measurements Akihisa Aikawa, Hirotaka Sakaue Anodized-aluminum temperature-sensitive paint (AA-TSP) is developed to capture the flow fields related to the temperature. Instead of using conventional polymer type TSP, the anodized-aluminum coating can hold material properties from cryogenic to high temperatures limited by its melting point of $\sim$ 930 K. We studied various luminophores onto this coating as a global temperature sensor. Six different quantum dots, which varied the luminescent peak wavelengths, are applied onto this coating. Rhodamine-B, pyronin B, pyronin Y, and europium complex are studied, which are also good candidates as the temperature sensing probes. The temperature calibrations of the developed AA-TSP are shown. The temperature is varied from 100 to 500 K. The temperature sensitivities of the developed AA-TSPs are related to the temperature range calibrated. Comparisons of the AA-TSPs related to the sensitive temperature range are included. A global temperature measurement in a hypersonic wind tunnel is shown as a demonstration of the developed AA-TSPs. [Preview Abstract] |
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LA.00020: Dual luminescence imaging applied for capturing the temperature distribution of a super-cooled droplet in collision icing Katsuaki Morita, Koji Okamoto, Hirotaka Sakaue Dual luminescence image is applied to capture the temperature distribution of a super-cooled droplet in icing when the droplet collides onto a plate. The imaging technique captures the temperature-sensitive luminescence and the temperature-insensitive luminescence, which are spectrally separated. These images are captured by a hi-speed color camera. The icing process from super-cooled condition to ice gives insight into further understandings of the icing in flights, power cables, architectures, etc. The icing formation is shown by time steps by using the hi-speed camera. The formation is discussed from the images captured. The plates are coated with icephobic coatings to understand their effects on the collision icing. [Preview Abstract] |
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LA.00021: ABSTRACT WITHDRAWN |
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LA.00022: Influence of local parameters on the dispersion of traffic-related pollutants within street canyons Styliani Karra, Liora Malki-Epshtein Ventilation within urban cities and street canyons and the associated air quality is a problem of increasing interest in the last decades. It is important for to minimise exposure of the population to traffic-related pollutants at street level. The residence time of pollutants within the street canyons depends on the meteorological conditions such as wind speed and direction, geometry layout and local parameters (position of traffic lane within the street). An experimental study was carried out to investigate the influence of traffic lane position on the dispersion of traffic-related pollutants within different street canyons geometries: symmetrical (equal building heights on both sides of the street), non-symmetrical (uniform building heights but lower on one side of the street) and heterogeneous (non-uniform building heights on both sides of the street) under constant meteorological conditions. Laboratory experiments were carried out within a water channel and simultaneous measurements of velocity field and concentration scalar levels within and above the street canyons using PIV and PLIF techniques. Traffic -related emissions were simulated using a line emission source. Two positions were examined for all street geometries: line emission source was placed in the centre of the street canyon; line emission source was placed off the centre of the street. [Preview Abstract] |
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LA.00023: Wake Structure of Oscillating Cylinders Michael Cohrs, Wayne Ernst, Ashwin Vaidya We studied the vortex-induced oscillations of a tethered cylinder in a flow tank. The cylinder shows various changes (steady, periodic, autorotation) in its orientation as a function of Reynolds number and particle aspect ratio. In particular, we examine a new metric- namely, the distance from the cylinder to the vortex as a function of the Reynolds number. This simple metric proves to be very helpful in characterizing the changes in vortex structure and serves as a useful marker for the various bifurcations in the flow. It is implied through data visualization that this critical point (which indicates a change in wake structure) is present regardless of the lengths of the cylinders. We examined Reynolds numbers in the range of about Re = 550 to Re = 4800, based on the cylinder's length. We also examined relationships between Strouhal number for the particle and associated vortex as a function of Reynolds number and particle aspect ratio. [Preview Abstract] |
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LA.00024: The mass, energy, space and time systemic theory- Black hole will take the dark comet to impact our earth Dayong Cao Our solar system has a companion black hole-``Tyche.'' A black hole have many dark planets (dark comets) like that Sun have many planets. The companion black hole could take its dark comets to go into our solar system, So there are a lot of dark comet near the orbit of Jupiter. The companion black hole go near our solar system every 25-27 million years. It could take its dark comets to impact our earth and could trigger the Mass Extinction. The black hole is the space-time center like a dark gas ball. So it absorb the space-time to go to its center like that Sun absorb the mass of matter by the gravity. Because it can absorb the space-time, when the companion black hole go near our solar system, it can cause the expand of space-time of solar system and the red-shift of our observation. The new idea will instead of the ``cosmic inflation''. The black hole and sun build up a system together. When the black hole inbreak our solar system in 20 years, not only it will break our environment, but aslo it will change the systemic genetical code of our life and thing. So it will kill many lives and will produce new life. So it could trigger the Mass Extinction. [Preview Abstract] |
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LA.00025: The mass, energy, space and time systemic theory-MEST Dayong Cao The displacement and period of the orbit of the motion are the space-time; the probability of them are the quantum space-time. Both of the energy-momentum tensor and metric tensor belong to the gravitational field. It can direct the space-time. The black hole has a space-time center as a origin of a mass-energy coordinate system and a binding energy of space-time like that sun has a mass-energy center and the nuclear energy. And it has a dark matter field around. There is a balance energy equation between sun and black hole. \begin{equation} E=h\nu=mc^2 \end{equation} Among it, E: the energy of wave of sun, m: the mass of wave, c: the velocity of wave, $\nu$: the frequence of wave, h: the Planck constant. \begin{equation} E'{\psi}=i{\hbar}\frac{\partial{\psi}}{{\partial}t} \end{equation} \begin{equation} m'{\psi}=-i{\hbar}\frac{{\partial}{\psi}{\partial}t} {{(\partial}x)^2} \end{equation} Among it, $E'\psi$: the energy of dark wave of black hole, $m'\psi$: the mass of dark wave, c$'$: the velocity of dark wave, ${\psi}$: the Wave Functions. \begin{equation} h\nu+E'{\psi}=mc^2+m'{\psi}c'^2, (c'^2=-\frac{({\partial}x)^2} {({\partial}t)^2}) \end{equation} [Preview Abstract] |
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LA.00026: ABSTRACT WITHDRAWN |
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LA.00027: Axially asymmetric rotating tank experiments for thermally forced stationary waves in geophysical fluids Huei-Ping Huang, Julian Hunt, Ashish Sharma, Louis Tse, Harindra Fernando, Andrey Gunawan, Patrick Phelan, Arthur Madrid, Michael Thompson Fluid dynamical experiments using a rotating tank with an imposed radial temperature gradient provide classical examples of the realization of large-scale atmospheric circulation in a laboratory setting. The last decade has seen a revival of such experiments for research and education. Classical rotating tank experiments have adopted axially symmetric boundary conditions to maintain a zonally uniform ``pole-to-equator'' temperature gradient. Symmetry breaking arises from internal dynamics of baroclinic instability. A notable exception is the class of experiments for topographic effects, in which an isolated obstacle is added to the bottom boundary. This study explores a new type of experiments that are axially asymmetric due to an imposed, zonally non-uniform, temperature in the lateral boundary. This mimics the contrast of warm pool versus cold tongue in the tropical Pacific Ocean. The experiments produced thermally forced quasi-stationary waves with their wavelength comparable to the scale of the localized thermal boundary forcing. The applications of this new type of experiments to understanding Earth's climate will be discussed. [Preview Abstract] |
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LA.00028: Possible Electrostatic Precursors to Granular Slip Events Troy Shinbrot, Nirmal Thyagu For at least the past 40 years, reports have repeatedly appeared of atmospheric lightning and related effects preceding major earthquakes. Many of these reports are anecdotal and of uncertain reliability, while others appear to have been substantiated by more recent scientific electric field measurements. In this work, we describe laboratory experiments that appear to exhibit sporadic, but statistically significant, electrical precursors to granular slip events. The cause of this phenomenon is unclear: the materials used are neither piezoelectric nor triboluminescent. We speculate that the electrical signals may be related to other electrical phenomena known to be associated with material failures in other contexts, for example in crack formation and in tape peeling. [Preview Abstract] |
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LA.00029: The formation of bulges and coastal currents from buoyant outflows Pablo Huq Buoyant outflows exiting (e.g. from an estuary or a sea strait) to the coastal ocean may form large bulges and coastal currents which propagate downshelf. Laboratory experiments show that the effect of the earth's rotation is to deflect the trajectory of the buoyant outflow into an inertial circle so that the buoyant outflow impacts the coastline further downshelf at an impact angle $\phi$. Bulges form if $\phi$ is larger than 60$^{\circ}$. Bulges store a significant fraction of the buoyant outflow; this attenuates the scales of the downshelf coastal current. The characteristics of the coastal current also depend on the ambient depth parameter, h/H, and the bottom slope parameter R/y$_{B}$. The width of the outflow also influences whether or not bulges form; bulge formation is described by a two-parameter space comprising the ambient depth parameter h/H and the Kelvin number K. Comparisons are made with oceanic observations. [Preview Abstract] |
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LA.00030: Lattice Boltzmann inverse modeling of water flows in the Everglades National Park Andrew Pearson, Michael Sukop, Victor Engel Knowledge of water flow in the Everglades National Park is vital for ecosystem restoration efforts. Of interest here is the planned rehabilitation of ``ridge-and-slough'' habitats, characterized by numerous adjacent sawgrass ridges aligned parallel to the flow direction. In many areas, reduced water flow due to water management systems has resulted in the conversion of ridge-and-slough landscapes into dense sawgrass stands. Previous studies of water flow have included tracer experiments, typically performed at several points in the region, with measurements taken over several days. Here we report initial results of inverse modeling of data from the EverTREx series of experiments using the parameter estimation code PEST coupled with a Lattice Boltzmann code. We perform two-component simulations in two dimensions, using satellite imagery to model the presence of vegetation in analogy with a porous medium. The final goals of this project are to reduce or remove the need for on-the-ground experiments for determining water flow characteristics in the Everglades, and to predict the effect of changes in water management systems on the flow. [Preview Abstract] |
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LA.00031: Effective Interactions Between Intruders in Vibrated Granular Materials Rachel Derby, Brian Utter Despite the strong fluctuations in a rapidly moving granular material, dissipation and correlations in collisions can lead to long range forces in granular materials. In this experiment, we study the long-range attraction between two objects when immersed in a vibrated granular system. Depending on the strength of vibration, a granular system can take the form of a gas or be fluidized. We place two large intruders in each of these systems to track the effective interactions between the intruders, varying frequency, amplitude, size of grains, and the shape of the intruder. In particular, we study the interaction of spheres in a granular gas and the effective force between plates in a granular fluid. Using image processing, we track the separation of the intruders over time. We find that parallel plates attract if they are separated by less than approximately 15 particle diameters and reach a final position in which one ordered layer of grains is between them. Granular gas experiments suggest a long-range interaction, but observed effects in the mean position are much weaker than the fluctuations. Ongoing work focuses on varying the vibration parameters (amplitude, frequency, {\&} waveform) and increasing statistics. [Preview Abstract] |
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LA.00032: Effects of Shear Thickening Properties in Oscillating Non-Newtonian Fluids Roxanne Able, Yogi Patel, Jon Bougie We study the behavior of a shear-thickening, non-Newtonian fluid when shaken at a variety of accelerational amplitudes and frequencies. Mixing corn starch with water, using cesium chloride to match density and prevent separation, produces a fluid with shear thickening properties. When a thin layer of this fluid is vertically oscillated, it can produce Faraday waves as well as other phenomena that are characteristic of non-Newtonian fluids, such as stable holes and time-dependent, delocalized regions that grow from small initial disturbances in the fluid layer. We investigate how the concentration of corn starch (and as a result the shear-thickening properties of the fluid) affects which phenomena are observed, and we demonstrate that this concentration does have a significant effect on the fluid behavior. [Preview Abstract] |
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LA.00033: Pulsed laser induced self-assembly of nanoparticle arrays: Competing liquid phase instabilities J.A. Diez, A.G. Gonzalez, Y. Wu, J.D. Fowlkes, N.A. Roberts, P.D. Rack, L. Kondic Thin film copper rings were synthesized on silicon dioxide thin films with various radii, thicknesses and widths and were subsequently liquefied via a nanosecond pulse laser treatment. During the nanoscale liquid lifetimes, the rings experience competing retraction dynamics and thin film and/or Rayleigh-Plateau type of instability, which lead to arrays of ordered nanodroplets. Ultimately, the original geometry dictates the instability pathway, which for narrow rings obeys the Rayleigh-Plateau type of instability, while for wider rings is influenced by the thin film instability. Hydrodynamic simulations describe well the observed time and length scales as well as the observed radial and circumferential instabilities which lead to different nanodroplet ensembles. [Preview Abstract] |
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LA.00034: Effect of viscosity ratio on liquid-liquid jets subjected to radial/axial electric field Siddharth Gadkari, Rochish Thaokar Linear stability analysis for viscous liquid-liquid electrified jets subjected to axisymmetric (m=0) and asymmetric (m=1) perturbations has been performed. Both radial and axial electric field configurations are considered and the importance of viscosity ratio ($\lambda $= viscosity of surrounding fluid/Viscosity of inside fluid) is studied. $\lambda $ is shown to have a damping effect on both the modes of perturbation. However the effect is more pronounced for the m=1 mode as compared to m=0 mode in the presence of electric fields. Viscosity ratio, along with electric field can control the dominance of individual modes. While m = 1 mode can only be realized in the lower $\lambda $ limit when radial field is on, it is always possible to realize m = 1 mode under axial fields provided the threshold field is applied. A phase diagram showing predominance of the two modes at any given value of electric field and viscosity ratio is generated for both axial and radial electric field setups. This phase diagram can serve as a guideline for the required set of operating parameters in order to suppress/realize any desired mode of instability. [Preview Abstract] |
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LA.00035: Kinetic approach to Kaluza's magnetohydrodynamics A. Sandoval-Villalbazo, L.S. Garcia-Colin Ten years ago we presented a formalism by means of which the basic tenets of relativistic magnetohydrodynamics were derived using Kaluza's ideas about unifying fields in terms of the corresponding space time curvature for a given metric.\footnote{A. Sandoval-Villalbazo and L.S. Garcia-Colin; Phys. of Plasmas 7, 4823 (2000).} In this work we present an attempt to obtain the thermodynamic properties of a charged fluid using using Boltzmann's equation for a dilute system adapted to kaluza's formalism. The main results that we obtain are analytical expressions for the main currents and corresponding forces, within the formalism of linear irreversible thermodynamics. We also indicate how transport coefficients can be calculated. Other relevant results are also mentioned. [Preview Abstract] |
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LA.00036: Effect of electrode geometry on charging of a water droplet in a dielectric liquid Myungmo Ahn, Do Jin Im, In Seok Kang Electrophoresis of a charged droplet (ECD) in a dielectric liquid can be used as a droplet manipulation method without complicated electrode or circuit design. For further utilization of its advantages, we need thorough understanding on the charging mechanism and the electrode geometry effect. We have investigated the effect of electrode geometry on the amount of charging experimentally and numerically. In the experiments, we have checked the difference of charge amount between the pin type and the plate type electrodes. A high speed camera and an electrometer are used for the measurement simultaneously. We also have calculated the charge amounts for both cases numerically. The charge amounts predicted from the simulation show good agreement with those of the experiments. In both cases, a droplet gets more charges on the pin type electrode. This result can be used for better design in the microfluidic applications using electric charging method. [Preview Abstract] |
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LA.00037: A microfluidic platform for impedance analysis and characterization of human umbilical vein endothelial cells Vanessa Velasco, Kenny King, Robert Keynton, Stuart Williams The characterization of endothelium morphology and permeability under fluid shear stress can provide essential information regarding the onset of different pathological conditions, as well as, the uptake of drugs and biomolecules. Real-time assessment of the integrity of cell monolayers and cell motility has been accomplished by implementing electrical impedance analysis. In this study, we report a micro-electrode array biosensor incorporated into a microfluidic platform for the impedance spectroscopy of Human Umbilical Vein Endothelial Cells (HUVECs) under physiological fluid shear stress. The biosensor consists of two adjacent and identical microfluidic channels which allows for simultaneous assessment of the electrical properties of a HUVEC monolayer and that of the cell culture media alone. Additionally, the biosensor is attached to a custom designed electronic system that simplifies the data acquisition and analysis of time-dependent multiplexed measurements for the different electrodes. The impedance spectrum (40 Hz to 10 MHz) was collected for HUVECs before and under different physiological fluid shear stress forces to yield insight to flow induced changes in HUVEC morphology, permeability, and relevant electrical parameters. This biosensor can be used as an \textit{in vitro} model of the endothelium for new drug discovery, as well as, part of biochemical assays for cell mechanism studies. [Preview Abstract] |
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LA.00038: Non-Newtonian behavior of magnetized ferrofluids as revealed by high speed x-ray phase contrast imaging Joy A. Prescod, A. Cali, S. Nunez, R. Smith, M. Vieira, A.D. Trubatch, P. Yecko, W.-K. Lee Objects moving through a magnetized ferrofluid experience enhanced drag as a result of the presence of magnetic particles and magnetic particle agglomerations which form due to magnetic attractive forces. The precise impact of an agglomeration on an object depends on the characteristics of the agglomeration, the relative sizes of the object and agglomeration, as well as other control parameters. In this study, high speed phase contrast imaging was used to directly image the impact of long thread-like magnetic particle agglomerations on the rheological properties of ferrofluids. Particularly, numerous types of interactions between these threads and translating objects, including free-falling 500 micron sized solid glass spheres and intermittently rising vapor bubbles were quantified. At these scales, objects may bind to particle threads resulting in momentary re-direction or arrest of the object's trajectory, alluding to a form of yield stress. Therefore, there is a macro-viscosity property in flows of this type, which has a potentially significant impact of the use of ferrofluids in micro-fluidics and drug delivery. [Preview Abstract] |
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LA.00039: DNA Size Segragation at a Convergent Stagnation Point James Boulger, Jennifer Kreft Pearce We investigate using counter-rotating vortices and a convergent stagnation point to segregate different sizes of DNA using a lattice Boltzmann based simulation with a bead-spring model for the polymer. We find that longer DNA molecules are left rotating in the fluid while shorter molecules aggregate at the stagnation point. The separation of the polymers depends on the fluid flow rate and a non-specific attractive force with the channel walls. We report on the robustness of this technique. [Preview Abstract] |
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LA.00040: Falling ball viscometry of magnetized ferrofluids Alex Cali, W.K. Lee, Samuel Nunez Jr., Joy Prescod, Rose Smith, A.D. Trubatch, Matthew Vieira, Philip Yecko Falling spheres of 500 $\mu$m were used to perform viscometric experiments on magnetized ferrofluids. The role of the angle of orientation of an applied unifom field relative to the direction of fall has been examined with high speed phase contrast imaging using the Advanced Photon Source. The magnetized ferrofluid exhibits an anisotropic viscosity that we can quantify in terms of a tensorial viscosity coefficient. We find that the effective drag is greater when the fall occurs normal to the applied field rather than parallel to it, a result that is opposite to what is predicted by many ferrofluid magnetoviscosity models, but consistent with the properties of electro- and magneto-rheological fluid, liquid crystal, and polymer fluid rheology models. Finally, we discuss the dispersion of these results in terms of thread-like aggregations of magnetic particles observed in the experiments. [Preview Abstract] |
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LA.00041: Ink transfer mechanism for gravure-offset printing by using flow visualization Seung-Hyun Lee, Ki-Sang Nam We investigated ink transfer mechanism for gravure-offset printing by monitoring ink transfer process. For convenient visualization of ink transfer, cantilever-type roll-to-plate gravure offset printing system is designed. We visualized ink transfer process from patterned plate to rolling blanket roller. Serial images were captured by using high-speed CMOS camera and long range microscope, and analyzed by image process. We investigated the rotational effect of blanket roller on ink transfer mechanism by comparing the ink transfer process with different pattern angle and printing speed. [Preview Abstract] |
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LA.00042: Enhanced evaporation from surfaces of width comparable to that of the mass boundary layer thickness Karine Ip, Shreyas Mandre We investigate the optimal distribution of spacing and size of stomata on a leaf, which enhances net evaporation rate. Although evaporation flux is known to be maximal at contact lines, is diffusion of the vapor also enhanced by the accompanying increase in the total perimeter when the contact lines are adjacent? The evaporation rate from the stomata is analyzed using a 1-D model for stomata distributions on a leaf and a 2-D convection-diffusion equation in the surrounding space. A universal behavior is observed as a function of the Peclet number Pe and stomata size. For stomata much wider than the mass boundary layer thickness, evaporation rate increases as the stomata are made smaller; but below a critical size, the evaporation rate saturates to a constant value. This transition occurs when stomata size is comparable to the mass boundary layer thickness. We experimentally tested this behavior with liquid evaporating from micro-channels of varying channel widths in a wind tunnel providing a range of Pe. [Preview Abstract] |
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LA.00043: Effects of Microstructural Parameters on Permeability of Fibrous Materials to Non-Newtonian Fluids B. Emami, H. Vahedi Tafreshi In this work, a series of numerical simulations has been devised to relate the non-Newtonian permeability constant of a fibrous medium to its Newtonian counterpart. Developing virtual 3-D geometries that resemble the internal microstructure of a fibrous material, we studied the effects of fiber diameter, fiber in-plane and through-plane orientations, and media's porosity on the media's permeability to Non-Newtonian fluids such as blood. The results of our digital experiments are used in conjunction with available analytical relations, derived to predict the non-Newtonian permeability constants of granular beds, to develop new empirical correlations for fibrous materials. [Preview Abstract] |
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LA.00044: Time resolved measurements of particle lift off from the wall in a turbulent water channel flow Rene van Hout, Boris Rabencov, Javier Arca Time-Resolved Particle Image Velocimetry (TR-PIV) and digital holography measurements were carried out in a dilute particle-laden flow tracking both Polystyrene Spheres (PS, $\sim $0.583 mm, $d^{+}\sim $10) as well as resolving the instantaneous velocity field of the turbulent flow. Measurements were performed in a closed loop, transparent, square channel facility (50x50 mm$^{2})$ at 127.5cm from the inlet with bulk water velocity 0.3 m/s (Re$_{h}$ = 7353) and friction velocity 0.0174 m/s. Data were captured at 1~kHz, corresponding to a time scale 5x smaller than the flow's viscous scale. Single view digital holographic cinematography was used to track the 3D PS motion inside the VOI (17x17x50 mm$^{3})$ including the wall bottom. TR-PIV in a vertical plane (29.3x29.3 mm$^{2})$ oriented along the channel's centerline imaged PS together with flow tracers. Discrimination was based on their size difference. Instantaneous sequences of PS plotted on the spatial velocity, vorticity and swirling strength maps showed the effect of turbulent flow structures and resulting particle movement. Results are presented for particles that lift off from the bottom wall as a result of complex interaction with ejection and sweep motions. [Preview Abstract] |
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LA.00045: Lagrangian particle tracking in strained and buoyant flows Armann Gylfason, Dimitry Ivanov, Lahcen Bouhlali, Chung-min Lee We present experimental particle tracking results in two turbulent flow configurations, straining flow and buoyant flow. Our focus is on the influence of large scale structure of such flows on the motions of passive and inertial particles, in particular acceleration statistics, Lagrangian structure functions, and two point statistics. The results are contrasted with previous work, and our results from approximately isotropic flows. The Eulerian structure of the underlying flow field is measured by applying the PIV method. [Preview Abstract] |
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LA.00046: Pore-scale Analysis of the effects of Contact Angle Hysteresis on Blob Mobilization in a Pore Doublet Shao-Yiu Hsu, Roland Glantz, Markus Hilpert The mobilization of residual oil blobs in porous media is of major interest to the petroleum industry. We studied the Jamin effect, which hampers the blob mobilization, experimentally in a pore doublet model and explain the Jamin effect through contact angle hysteresis. A liquid blob was trapped in one of the tubes of the pore doublet model and then subjected to different pressure gradients. We measured the contact angles (in 2D and 3D) as well as the mean curvatures of the blob. Due to gravity effects and hysteresis, the contact angles of the blob were initially (zero pressure gradient) non-uniform and exhibited a pronounced altitude dependence. As the pressure gradient was increased, the contact angles became more uniform and the altitude dependence of the contact angle decreased. At the same time, the mean curvature of the drainage interface increased, and the mean curvature of the imbibition interface decreased. The pressure drops across the pore model, which we inferred with our theory from the measured contact angles and mean curvatures, were in line with the directly measured pressure data. We not only show that a trapped blob can sustain a finite pressure gradient but also develop methods to measure the contact angles and mean curvatures in 3D. [Preview Abstract] |
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LA.00047: ABSTRACT WITHDRAWN |
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LA.00048: Effect on Turbulence Radiation Interaction in Particle Laden Flow Mathew Cleveleand, Sourabh Apte, Todd Palmer The effects of Turbulence Radiation Interactions (TRI) in particulate laden flows can significantly influence thermal radiation fields and corresponding material heating. Most combustion problems contain strong heterogeneities which can be treated stochastically. In pulverized coal combustion these heterogeneities include particulate such as coal, fly-ash, and char. This work expands upon a simplified test case, developed by Deshmukh et al. (Proc. Comb. Inst., 2009), to highlight the effects of fuel particulate on TRI phenomena. This includes the decaying isotropic turbulence with a single-step reaction in the presence of solid particulates. Three different test cases were studied: a simplified gas-phase combustion problem without particulate, non-reacting particulate in the gas-phase combustion, a solid-fuel/gas-oxidizer combustion model. Sensitivity of TRI uncertainties such as thermal radiation fields and thermal emission to the presence fuel particulates is investigated in this test problem using direct numerical simulation for the gas-phase and Monte-Carlo approach for the radiative heat transfer. [Preview Abstract] |
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LA.00049: Shooting inertial wave packets into rotating turbulence Eran Sharon, Ehud Yarom, Kobi Cohen We experimentally study the effect of localized fluctuations in energy injection rate on existing rotating turbulent flow. We show that such fluctuations generate packets of inertial waves, propagating along the axis of rotation. Close to the energy source the propagating pulses leave the steady turbulent field unaffected. Energy is transferred from the pulses into the steady turbulent field only at height h above the injection plane. This height is determined by equating the propagation time of an inertial wave to h, with the time for nonlinear interaction between the wave and the turbulent field. This mechanism, which allows ``shooting'' turbulence to selected heights, is expected to be important in rapidly rotating geophysical flows. [Preview Abstract] |
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LA.00050: Flow Instability in Channel Flow with a Streamwise-periodic Array of Circular Cylinders Kyongjun Lee, Dong-Hyeog Yoon, Kyung-Soo Yang A parametric study has been carried out to elucidate the characteristics of flow instability in laminar channel flow with a streamwise-periodic array of circular cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to a significant change in flow instability. There exist two kinds of instability; flow undergoes a primary instability (Hopf bifurcation) at a low Reynolds number, and the resulting time-periodic two-dimensional flow subsequently becomes unstable to three-dimensional disturbances at a higher Reynolds number (secondary instability). We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent time-periodic 2D flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinders and the channel wall. We also present a Floquet stability analysis on the time-periodic 2D flows to identify the onset of the secondary instability leading to 3D flow. [Preview Abstract] |
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LA.00051: Non-linear stability and transition analysis in reactive hypersonic shear-layers Luca Massa Carbon chemistry and the endothermic reactions it supports were previously shown to delay hypersonic boundary layer instability and transition. The present analysis addresses the analogous problem in free shear-layers and arrives to the conclusion that the lack of the acoustic trapping mechanism implies that endothermic chemistry can lead to stabilization or destabilization of the shear-layer depending on the free-stream temperature. This study identifies three mechanism by which carbon chemistry affects instability and transition. The first is rooted in the changes to the inflectional profiles caused by the visco- chemical interaction. The second is due to damping of the perturbation by finite rate chemistry. The third is linked to streamwise relaxation which delays the onset of secondary instability of vortical structures generated by a saturated primary instability wave. Linear analysis predicts changes in growth rate lower than 30\% for Mach numbers below 5. Nonlinear parabolized stability analysis predicts significantly larger differences, depending on whether the primary or secondary instability trigger the transition onset. [Preview Abstract] |
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LA.00052: Dispersion of capillary waves in elliptical cylindrical jets Ghobad Amini, Ali Dolatabadi In this work motion of a low speed liquid jet issuing from an elliptic orifice through the air is studied. Mathematical solution of viscous free-surface flow for this asymmetric geometry is simplified by using one-dimensional Cosserat (directed curve) equations which can be assumed as a low order form of Navier-Stokes equations for slender jets. Linear solution is performed and temporal and spatial dispersion equations are derived. Growth rate and phase speed of unstable and stable modes under various conditions are presented. The possibility of instability of asymmetric disturbances is studied too. With distance down the jet, major and minor axes are altered and finally jet breaks up due to capillary instability. The effect of jet velocity and viscosity and also orifice ellipticity on axis-switching and breakup is investigated. [Preview Abstract] |
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LA.00053: Influence of confinement by smooth and rough walls on particle dynamics in dense hard-sphere suspensions Burak Eral, Dirk van den Ende, Michel Duits, Frieder Mugele We used video microscopy and particle tracking to study the dynamics of confined hard-sphere suspensions. Our fluids consisted of 1.1-$\mu $m-diameter silica spheres suspended at volume fractions of 0.33--0.42 in water-dimethyl sulfoxide. Suspensions were confined in a quasiparallel geometry between two glass surfaces. First, as the separation distance (H) is decreased from 18 to 1 particle diameter, a transition takes place from a subdiffusive behavior (as in bulk) at large H, to completely caged particle dynamics at small H. These changes are accompanied by a strong decrease in the amplitude of the mean-square displacement (MSD) in the horizontal plane parallel to the confining surfaces. In contrast, the global volume fraction essentially remains constant when H is decreased. Second, measuring the MSD as a function of distance from the confining walls, we found that the MSD is not spatially uniform but smaller close to the walls.. Although confinement also induces local variations in volume fraction, the spatial variations in MSD can be attributed only partially to this effect. The changes in MSD are predominantly a direct effect of the confining surfaces. Hence, both the wall roughness and the separation distance (H) influence the dynamics in confined geometries. [Preview Abstract] |
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LA.00054: Large-scale structures of the turbulent boundary layer in wall-normal/spanwise plane Jae Hwa Lee, Jin Lee, Hyung Jin Sung Coherent wall-normal structures in turbulent boundary layer (TBL) have been investigated by scrutinizing the direct numerical simulation (DNS) dataset with \textit{Re}$_{\theta }$=2500. The spatial signatures of hairpin vortex legs were frequently observed in the vector fields of the wall-normal/spanwise (\textit{yz}) plane and it was found that groups of such hairpin legs induce wall-normal-aligned elongated structures with a large Reynolds shear stress; this result strongly supports the typical hairpin packet model. The two-point correlation of the velocity fluctuations showed that the wall-normal length scales vary linearly with the distance from the wall and the two-point correlations between the signed swirling motions showed that interactions between counter-rotating vortices are predominant throughout the boundary layer and especially frequent in the near-wall region. [Preview Abstract] |
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LA.00055: Observations of Anisotropy in Atmospheric Turbulence by Means of Moir\'{e} Deflectometry Saifollah Rasouli, M.D. Niry, Y. Rajabi, A.A. Panahi, J.J. Niemela We report observations of strong anisotropy in the statistical properties of atmospheric turbulence, using a method based on moir\'{e} deflectometry. By combining use of a telescope with moir\'{e} deflectometry we achieve a high sensitivity to fluctuations in the wave-front phase, which are, in turn, related to fluctuations in the fluid density. As phase fluctuations of the wave front in the aperature of the telescope are imaged on the first grating of the moir\'{e} deflectometer, a high spatial resolution is achieved. Experimentally, we measure covariance of angle of arrival (AA) between pairs of points displaced spatially on the telescope aperature and find significant differences between scaling exponents derived for covariances in the longitunal and transverse directions. We note that the method does not require the use of the Taylor hypothesis and has the advantage of being relatively simple and inexpensive. [Preview Abstract] |
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LA.00056: Large Eddy Simulation of Turbulent Flow in a Ribbed Pipe Changwoo Kang, Kyung-Soo Yang Turbulent flow in a pipe with periodically wall-mounted ribs has been investigated by large eddy simulation with a dynamic subgrid-scale model. The value of Re considered is 98,000, based on hydraulic diameter and mean bulk velocity. An immersed boundary method was employed to implement the ribs in the computational domain. The spacing of the ribs is the key parameter to produce the d-type, intermediate and k-type roughness flows. The mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the experimental measurements currently available. Turbulence statistics, including budgets of the Reynolds stresses, were computed, and analyzed to elucidate turbulence structures, especially around the ribs. In particular, effects of the ribs are identified by comparing the turbulence structures with those of smooth pipe flow. The present investigation is relevant to the erosion/corrosion that often occurs around a protruding roughness in a pipe system. [Preview Abstract] |
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LA.00057: Simulation of Colliding Vortex Rings and Parallel Performance of Lattice Boltzmann Method Baili Zhang, Ming Cheng, Jing Lou Vortex motion or flow with vorticity plays an essential role in almost all kinds of fluid motion of interest. In order to investigate the mechanisms of vortex reconnection, numerical simulation of collision of two vortex rings in three dimensions was carried out using lattice Boltzmann method. We have studied several runs with different initial angles and positions of the ring planes, i.e., head-on collision, inclined collision and off-side collision, keeping the other parameters fixed. However, in order to achieve high resolution on vortex reconnection and its coherent structures, hundreds million of lattices are often necessary in a three dimensional domain, parallel implementations are adopted to attend the demand of an expressive memory amount and processing power of the method. Two vortex collisions have been used as case study to evaluate our implementation, and very good parallel performance was achieved up to thousands of CPUs in a distributed computer system. The lattice Boltzmann method has proved to be an important technique for the numerical solution of partial differential equations because it has nearly ideal scalability on parallel computers for many applications. [Preview Abstract] |
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LA.00058: ABSTRACT WITHDRAWN |
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LA.00059: Nonlinear pulsations of a Hamiltonian system of the fourth order by a nonlinear trigonometric series George Miroshnikov Dynamics of Hamiltonian systems is the key issue of solitary waves since the initial-value problems on free surfaces and interfaces are reduced to Hamiltonian problems in the reference frame moving with the wave. The Hamiltonian approach covers applications at high Reynolds numbers, which range from the famous irrotational Boussinesq-Rayleigh solitary wave to the rotational waves with a uniform vorticity. The Hamiltonian system with a polynomial potential of the fourth order is studied in the asymmetric case of subcritical periodic pulsations by using a nonlinear trigonometric series in even powers of cosine. The series solutions are computed symbolically and compared with the numerical solution using the Fehlberg fourth-fifth order Runge-Kutta method with degree four interpolant. It is shown that the series solutions with uniform convergence are superior to the numeric solutions with local convergence. The qualitative comparison of the theoretical solutions with the experimental profiles of the Geminga pulsar is also provided. [Preview Abstract] |
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LA.00060: Thermophoresis of a thermally responsive polymer Klinton Kilgore, Jacob Ford, Jennifer Kreft Pearce Thermophoresis is the migration of a species in response to a temperature gradient. This mechanism can be used to manipulate molecules in microfluidic channels. We experimentally investigate thermophoresis of a synthetic polymer. The polymer is thermally responsive and changes conformation in aqueous solution at the cloud point temperature. Two forms of the polymer are present in the temperature gradient at an average temperature near the cloud point, with one conformation migrating to the hot side of the channel and the other to the cold. We also investigate the polymer's migratory dependence on dissolved ionic species, specifically NaCl, which changes the cloud point temperature. We examine the effect of the conformation change on thermophoresis using a lattice-Boltzmann- based simulation. [Preview Abstract] |
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LA.00061: An experimental investigation of the multiphase flows in a photobioreactor for algae cultivation Zifeng Yang, Hui Hu, Matteo del Ninno, Zhiyou Wen Algal biomass is a promising feedstock for biofuels production, with photobioreactors being one of the major cultivation systems for algal cells. Light absorption, fluid dynamics, and algal metabolism are three key factors in determining the overall performance of a photobioreactor. The behavior of the multiphase flow (i.e., liquid phase -- water, gas phase -- CO$_{2}$ and O$_{2}$, and solid phase -- algal cells) and turbulent mixing inside the reactor are the core connecting the three factors together. One of the major challenges in the optimal design of photobioreactors for algae cultivation is the lack of in-depth understanding of the characteristics of the multiphase flows and turbulent mixing. In this study, we present a comprehensive experimental study to investigate the effects of turbulent mixing in photobioreactors on the performance of a photobioreactor for algae cultivation. A high-resolution particle image velocity (PIV) system is used to achieve time-resolved, in-situ flow field measurements to quantify the turbulent mixing of the multiphase flows inside the bioreactor, while algal cultures are also grown in the same reactor with the same experimental settings. The mixing characteristics of the multiphase flow are correlated with the algal growth performance in the bioreactors to elucidate the underlying physics to explore/optimize design paradigms for the optimization of photobioreactor designs for algae cultivation. [Preview Abstract] |
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