Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session JU: Poster Session: 15:35-17:00 |
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Room: Salt Palace Convention Center Ballroom A-D |
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JU.00001: The Aeroacoustics of Turbulent Coanda Wall Jets Caroline Lubert, Jason Fox Turbulent Coanda wall jets have become increasingly widely used in a variety of industrial applications in recent years, due to the substantial flow deflection that they afford. A related characteristic is the enhanced turbulence levels and entrainment they offer, compared with conventional jet flows. This characteristic is, however, generally accompanied by a significant increase in the noise levels associated with devices employing this effect. As a consequence, the potential offered by Coanda devices is yet to be fully realized. This problem provides the impetus for the research detailed in this poster. To date, some work has been done on developing a mathematical model of the Turbulent Mixing Noise emitted by such a device, assuming that the surface adjoining the turbulent flow was essentially 2-D. This poster extends this fundamental model, through a combination of mathematical modeling and acoustical and optical experiments. The effect of a variety of parameters, including nozzle configuration and jet exit velocity will be discussed, and ways of reducing or attenuating the noise generated by such flow, whilst still maintaining the crucial flow characteristics, will be presented. [Preview Abstract] |
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JU.00002: Reduction of shock induced noise in imperfectly expanded supersonic jets using convex optimization Sam Adhikari Imperfectly expanded jets generate screech noise. The imbalance between the backpressure and the exit pressure of the imperfectly expanded jets produce shock cells and expansion or compression waves from the nozzle. The instability waves and the shock cells interact to generate the screech sound. The mathematical model consists of cylindrical coordinate based full Navier-Stokes equations and large-eddy-simulation turbulence modeling. Analytical and computational analysis of the three-dimensional helical effects provide a model that relates several parameters with shock cell patterns, screech frequency and distribution of shock generation locations. Convex optimization techniques minimize the shock cell patterns and the instability waves. The objective functions are (convex) quadratic and the constraint functions are affine. In the quadratic optimization programs, minimization of the quadratic functions over a set of polyhedrons provides the optimal result. Various industry standard methods like regression analysis, distance between polyhedra, bounding variance, Markowitz optimization, and second order cone programming is used for Quadratic Optimization. [Preview Abstract] |
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JU.00003: Cross sectional image of the pipe flow with periodical side flow injection Toshihisa Ueda, Yuusuke Sugikawa, Naotaka Higuchi Mixing is one of the essential processes in most industries. The enhancement of mixing and reaction in laminar conditions plays an important role in high viscous fluids, a flow in microsystems , chemical- and bio- reactors. In the present study, periodical flow motion is investigated to enhance the mixing. The experimental apparatus consists of a main flow pipe and four branching flow pipes which is installed normal to the main pipe. Glycerin is used as a working fluid. The glycerin flows in a steady state condition in the main pipe while the branching flow is injected periodically from four pipes. The cross sectional image of the mixing of main flow and branching flows is visualized by inserting the Rodamin B in the first branching flow. The laser sheet is formed at the test cross section and the location of the branching flow is visualized. When only one branching flow is periodically injected, a simple circle pattern is periodically formed at the cross section. When the number of the branching flow is increased, the cross sectional pattern becomes complex and the interface between main flow and branching flow increases, which results in an increase in the molecular diffusion and enhance the mixing. [Preview Abstract] |
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JU.00004: Multifractal Analysis of Taylor-Couette Flow with Hourglass Geometry in both Laminar and Turbulent Regimes Adam Kowalski, Thomas Olsen, Richard Wiener Previously we have presented Correlation Dimension and Kaplan-Yorke Dimension analyses of the irregular generation of new Taylor Vortex Pairs in both laminar and turbulent Taylor-Couette flow with hourglass geometry could be characterized as low dimensional chaos\footnote{A. Kowalski, T. Olsen, \& R. Wiener, Bull. Am. Phys. Soc. \textbf{50-9}, P1.00030 (2006).}. We now present a multifractal analysis\footnote{J. A. Glazier \& A. Libchaber, IEEE Trans. On Circuits and Systems \textbf{35-7}, 790 (1988).}$^,$\footnote{T. Halsey, M. H. Jensen, L. P. Kadanoff, I. Procaccia, \& B. I. Shraiman, Phys. Rev. A \textbf{33}, 1141 (1986).} of the same data. We comment on the additional insights into the physical process provided. [Preview Abstract] |
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JU.00005: The Damped, Driven Pendulum as a Test Case for Algorithms to Control Low Dimensional Chaos Lucas Hill, Thomas Olsen, Richard Wiener Previously, we have employed the Recursive Proportional Feedback algorithm\footnote{Rollins \textit{et al}, Phys. Rev. E \textbf{47}, R780 (1993).} to achieve control of the chaotic formation of Taylor-Vortex pairs in Modified Taylor-Couette flow with hourglass geometry\footnote{Wiener \textit{et al}, Phys. Rev. Lett. \textbf{83}, 2340 (1999).}. We have developed analogous algorithms and seek to test them in a more easily accessible system to test them prior to implementation in the Taylor-Couette system. To this end we have implemented a damped driven mechanical pendulum\footnote{J. A. Blackburn \textit{et al}, Rev. Sci. Instr. \textbf{60}, 422 (1989).}. We report on the measures of chaos and the application of control algorithms. [Preview Abstract] |
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JU.00006: Reaction-Diffusion Model Simulations of Varying Lengths Employed to interpret Chaotic Taylor Vortex Formation in Modified Taylor-Couette Flow Yunjie Zhao, Andrew Halmstad, Thomas Olsen, Richard Wiener Previously, we have observed a period-doubling cascade to chaos in Modified Taylor-Couette Flow with Hourglass Geometry\footnote{Richard J. Wiener \textit{et al}, Phys. Rev. E \textbf{55}, 5489 (1997).}. Such behavior has been modeled by The Reaction-Diffusion equation\footnote{H. Riecke and H.-G. Paap, Europhys. Lett. \textbf{14}, 1235 (1991).}. In the experiment, chaotic formation of Taylor-Vortex pair formation was restricted to a very narrow band about the waist of the hourglass. The calculations of Riecke and Paap suggested that a quadrupling of the length of the system would lead to spatial chaos in the vortex formation. We present a careful recreation of the previous calculation and consider an intermediate length. We demonstrate that doubling the length should be sufficient to observe spatially chaotic behavior. [Preview Abstract] |
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JU.00007: Modeling of Bio-Fluids Flow with Complex Geometry Using Immersed Boundary Method Shaolin Mao, Ismail Celik Fluid dynamics problems in the area of bio-fluids involve complex geometries and moving boundaries in addition to strong transients. The applications of CFD to such problems traditionally employ boundary fitted coordinates, which require generation of complicated computational grids. The alternative approach utilizing Cartesian coordinates with embedded virtual force method (immersed boundary method) avoids the problem of expensive and time consuming boundary fitted grid. The simple orthogonal grids directly benefit numerical accuracy and computational efficiency. An immediate application of immersed boundary method (IB) is to modify in-house CFD DREAM code for bio-engineering applications using domain decomposition methodology. Several benchmarks are tested and numerical results for gas-droplet two-phase flow are shown to examine the transport and dispersion of germ-laden droplets in a room. This modeling effort provides valuable information for ventilation control strategies to improve airflow patterns to reduce indoor airborne infection risk. [Preview Abstract] |
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JU.00008: Lattices for lattice Boltzmann methods Shyam Chikatamarla, Iliya Karlin The lattices widely used for lattice Boltzmann methods (LBM) viz., the 3 velocity lattice in 1D, $3^2$ in 2D and $3^3$ in 3D (including its prunes 15 and 19 velocity lattices) are simplest or lowest order approximations to the Boltzmann BGK equation. Although, these approximations (lattices) have been successful in simulating simple isothermal flows, they introduce significant errors for complex flows like compressible flows, multiphase flows, micro flows etc. The above mentioned lattices can be collected into order-3 or three velocity set approximations in a hierarchical approximation to the Boltzmann equation. Thus, higher order approximations to the Boltzmann equation are first derived in 1D and then extended to higher dimensions [Chikatamarla \textit{et al.},\textit{Phys Rev Lett} 97 (19): No. 190601 (2006)]. The thermodynamic consistency and stability of these newly identified lattices is ensured via entropic construction of LBM [Karlin \textit{et al.}, \textit{Europhys. Lett.} 47 (2): 182 (1999)]. In this work, all possible lattices are identified, to any desired accuracy, in all three dimensions. Superiority of these new lattices and the entropic construction of LBM are demonstrated. Finally, a computationally efficient implementation of LBM models, via the product form of evaluation of equilibrium [Chikatamarla \textit{et al.}, \textit{Phys. Rev. Lett.} 97 (1): No. 010201 (2006)], is presented. [Preview Abstract] |
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JU.00009: Modeling Flow and Turbulence in Forest Canopies Brandon Little, Aric McLanahan, Steve Edburg, David Stock, Brian Lamb Control strategies for mountain pine beetles often include releasing trace concentrations of pheromone mimics into the forest canopy. For such a release to be effective for control, diffusivities within the canopy must be known. To compute flow within the canopy, the trees are treated as a porous medium by including sink/source terms in the momentum equations. Trees also affect turbulence within the canopy. With RANS models, sink/source terms can be added to the kinetic energy and dissipation equations to account for this change, but the best form of these added terms is not known. A one-dimensional momentum equation with a k-$\varepsilon $ closure was used to study various forms of the sink/source terms for k and $\varepsilon $ for a homogeneous forest with a neutrally stable flow. A new form of the sink/source terms that models the turbulent length scales in the canopy best matched the field data [Preview Abstract] |
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JU.00010: Thermal Management of Electronic Chips in a Channel Using Input Power to Control Flow Velocity Esam Alawadhi In this research, thermal management control of electronic chips is investigated using the input power. The examined system consists of two-parallel plates containing three heated chips attached on the lower plate. Time-dependent heat flux is supplied at the base of the chips to simulate a real operation for an electronic device. The value of the channel's inlet velocity is varied with the heat flux variations. The problem is solved as a conjugate heat transfer problem, and the finite element method is utilized to solve the problem. The effects of the heat flux oscillating period and amplitude, and Reynolds number are investigated. The heat flux applied to the chips is varying harmonically, but the channel's inlet velocity was kept time-independent. Results indicate that the variations of the heat flux significantly affect the Nusselt number at the surface of the chips exposed to the flow. Dynamics changing of the flow streamlines and the temperature contours are presented. [Preview Abstract] |
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JU.00011: Heat and fluid flow in a modified Rayleigh-Benard cavity with an inverted-V upper plate Antonio Campo, Hassan Ridouane, Jane Chang The heat and fluid flow characteristics of air inside a modified Rayleigh-Benard (RB) cavity with a lower flat plate and an inverted-V upper plate has been investigated numerically using the finite-volume method. The problem is controlled by two parameters: (1) the Rayleigh number Ra and (2) the relative height of the vertical sidewalls d. The numerical velocity and temperature fields are presented in terms of streamlines, isotherms, local and mean heat fluxes. The critical Ra values descriptive of the transition from symmetrical to asymmetrical buoyant airflow due to incremental changes in Ra were determined. A general correlation equation for the Nusselt number in terms of Ra and the dimensionless d was developed using nonlinear multiple regression theory. [Preview Abstract] |
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JU.00012: The height and temperature effects on the Leidenfrost phenomenon with hastelloy Satoshi Yoshida, Mezbah Uddin, Satoshi Someya, Koji Okamoto The interaction phenomena of one drop impinging on a hot surface around Leidenfrost temperature have been experimentally investigated. In this experiment especially droplet interaction behavior with respect to the different droplet height was analyzed with high speed camera at 5000 frame per second. A large influence on the Leidenfrost phenomena of hastelloy and several materials was determined. In addition to the hastelloy, SUS 304, SUS 316, Aluminum, Titanium and Zircalloy were used as specimens. It has been observed that with increasing the droplet falling height, evaporation time of the droplet was decreased. At a certain droplet falling height and surface temperature, a droplet jet extraction phenomenon has been observed. Because of the vaporization at the first impact of the droplet bottom, the vaporization pressure attack top of the droplet, then the jet has been extracted from top of the droplet. At higher droplet falling distance and temperature, the jet extraction phenomenon does not occur, since the droplet has higher impact moment. [Preview Abstract] |
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JU.00013: Low-frequency instabilities in the presence of inhomogeneous parallel flows Sudip Sen Here we present a novel theory in fluid flow instabilities, which has significant implications in our conventional knowledge in various areas, from basic fluid dynamics, fusion technology to space sciences. We have shown that (contrary to the usual believe that a parallel flow shear (first spacial derivative) is always destabilizing to various fluid instabilities) the destabilizing influence of the shear in the parallel flow can be suppressed altogether if one takes the effect of the flow curvature (second spatial derivative) into account. The transverse curvature in the parallel flow can overcome the destabilizing influence of the shear and can render the low frequency modes stable. This novel theory is applicable to various low-frequency waves and instabilities in various physical systems from laboratory, space, high temperature plasma and fluid medium to magnetohydrodynamics. This is because it is only natural that all actual flow profiles must in principle be curved rather than a pure straight line (only in this case the flow shear will be relevant), the inclusion of curvature in the flow profile rather than the shear alone is therefore more realistic. [Preview Abstract] |
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JU.00014: Laboratory and numerical studies of stratified spin-up flow stability Sergey Smirnov, Rafael Pacheco The stability of stratified rotating flows is investigated by means of laboratory experiments and numerical simulations in axisymmetric cylindrical and annular containers with both horizontal and sloping bottoms. The baroclinic current in initiated via incremental spin-up/down of a linearly stratified fluid by an abrupt change in the rotation rate of the system. The flow stability depends on the characteristic values of the Rossby number, $\varepsilon =\Delta \Omega $/$\Omega $, and the Burger number, $B_{u}$ = \textit{NH}/\textit{fR}, where $f$ = 2$\Omega $ is the Coriolis parameter, $R$ is the characteristic horizontal length scale of the flow, $H$ is the depth of the fluid layer, and $N$ is the buoyancy frequency. Particular attention is given to the nonlinear flow regime (finite Rossby numbers). It is found that axisymmetric spin-up current loses its azimuthal symmetry when $B_{u} \quad <$ 1, and breaks into a system of large-scale cyclonic and anticyclonic vortices with predominantly vertical axis of rotation. The eddies always develop at the density fronts formed by the corner regions adjacent to the sidewalls of the container. It is also shown that the stability of the spin-up flow is affected by the bottom slope. In the presence of the latter the bottom boundary layer experiences a qualitatively different behavior. While the density field demonstrates a smooth monotonic behavior in the case of stratified spin-up at all times, it reveals high-frequency fluctuations in the spin-down case. [Preview Abstract] |
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JU.00015: Turbulence characteristics of flow over two dimensional dunes in the presence of surface waves Satya P. Ojha, Bijoy S. Mazumder This paper presents the results of an experimental study of flow over asymmetric wavy bottom boundary in the presence of surface waves carried out in a laboratory flume. The bottom of the flume is made wavy by fixing 12 asymmetric dunes of mean length 32 cm and mean height 3 cm. Four types of experiments were performed, one with current alone and three with combined wave-current flow with three different wave frequencies. A 3-D Micro ADV is used for turbulent velocity measurements. The effect of wave superposition is to increase flow resistance. Moreover, the apparent bottom roughness is found to increase with increasing wave frequency. The suspended sediment concentration is also found to change with addition of surface waves. [Preview Abstract] |
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JU.00016: Radial band formation in binary mixtures of flowing granular media in a tilted tank William Hourigan, Thomas Ward The formation of radial band of glass beads in a variable-sized grain mixture in a tilted rotating tank is examined experimentally for angles between 15$^{\circ}$ and 65$^{\circ}$ from the horizon and for rotation speeds $\le 50$ RPM. The mixture is composed of glass beads of two sizes; which have diameters between $100-600 \mu$m. Images are recorded of band formation for differing concentrations. We examine the width of the band and the distance from the bottom surface of the tank as a function of the concentration, tilt angle and speed. [Preview Abstract] |
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JU.00017: Interfacial instability of a miscible ferrodroplet immersed in a thin layer of solvent Ching-Yao Chen, W.-K. Tsai We experimentally study the interfacial instability of a ferrodroplet immersed in a thin layer of solvent and subjected a perpendicular uniform field. Affected by the magnetic field, an interesting interfacial instability, which is a new mixed type of Rosensweig instability and miscible labyrinthine instability, is observed. Initially, the droplet is lifted by the perpendicular field and forms a typical Rosensweig peak along the field direction. On the other hand, confined by the thin layer of solvent, labyrinthine fingers are triggered by magnetization on the plane of substrate. Because of diffusion, the height of Rosensweig peak decays and serves as an injecting source to enhance the labyrinthine fingers. Consequently, very vigorous fingering is resulted. [Preview Abstract] |
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JU.00018: Finite Sample Effects in Temperature Gradient Focusing. Hao Lin, Jonathan Shackman, David Ross Temperature gradient focusing (TGF) is a new and promising microfluidic electrokinetic focusing method which can provide high concentration factors. In general TGF works in the linear regime where the analyte concentration is small when compared with buffer ion concentrations. However, this presumption may at times be violated. Under this situation strong nonlinear interactions between sample and buffer ions may occur, which eventually lead to peak shifting and distortion, and the loss of detectability and resolution. In this work we combine theory, simulation, and experiments to present a detailed study on nonlinear sample-buffer interactions in TGF. One of the key results is the derivation of a generalized Kohlrausch regulating function (KRF) that is valid for systems in which the electrophoretic mobilities are not constant but vary spatially. This generalized KRF greatly simplifies the analysis, reducing the problem to a single equation describing sample concentration evolution, and is applicable to other problems with heterogeneous electrophoretic mobilities. Using this sample evolution equation we have derived an understanding of the nonlinear peak deformation phenomenon observed experimentally in TGF. We have used numerical simulations to validate our theory, and to quantitatively predict TGF. Our results demonstrate excellent agreement with experiment. [Preview Abstract] |
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JU.00019: Field-effect control of ion-transport in nanofluidic channels Ankit Raj, Daejoong Kim, Mark Shannon Ion transport in nanoscale channels has recently received overwhelming attention due to various promising applications. The Debye length being comparable to the channel dimensions leads to some interesting consequences like ion-exclusion-enrichment effect. The flow is dominated by surface charges within the nanochannel due to high surface to volume ratio. By varying the surface charge at the walls of the nanochannel with the application of a gate voltage the flow of ions can be controlled due to its effect on the concentration of the co-ions/counter-ions inside the nanochannel. To observe the concentration polarization of ions due to a nanochannel and to get conductivity measurements, we have fabricated a planar nanochannel structure in a silicon-glass device using conventional micro-fabrication techniques with heavily doped silicon substrate as the gate electrode that can help vary the surface charge on the walls of a nanochannel. We study the concentration polarization for charged fluorescent dyes like fluorescein and rhodamine 6G and the effect of the gate potential on this phenomenon for various salt concentrations. Also, we measure the conductivity of ions through the nanochannel and can vary it with the application of a gate voltage. We present a detailed characterization of gate effect on ion-conductivity through nanochannels for various salt concentrations. [Preview Abstract] |
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JU.00020: Micromachined Fabry-Perot Interferometer with Embedded Nanochannels for Nanoscale Fluid Dynamics Frieder Mugele, Koen M. van Delft, Jan C.T. Eijkel, Helmut Rathgen, Albert van den Berg We describe a microfabricated Fabry-P\'erot interferometer with nanochannels of various heights between 6 and 20 nm embedded in its cavity. By multiple beam interferometry, the device enables the study of liquid behavior in the nanochannels without using fluorescent substances. During filling studies of ethanol and water, an intriguing filling mode for partially wetting water was observed, tentatively attributed to the entrapment of a large amount of gas inside the channels. [Preview Abstract] |
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JU.00021: Characteristic of Boundary Layer on a Continuous Moving Surface in Power Law Fluids Xinxin Zhang, Hao Zhang, Lianchun Zheng This paper presents a theoretical and numerical analysis of the boundary layer flow on a continuous moving surface in power law fluid. The estimated formulas for the laminar boundary layer thickness and the friction coefficient are obtained. The analogy between the thermal diffusivity and the kinematic viscosity is drawn and the power law model of the thermal diffusivity is established. The similarity equations of the boundary layer are obtained, which only involve two independent parameters: power law index and Prandtl number. The velocity distribution, the temperature distribution and the shearing stress distribution are obtained numerically by considering the effect of the power law viscosity on the viscous and thermal diffusivities. The results show that the dimensionless velocity distribution depends on the velocity ratio parameter of the plate and the power law index. The dimensionless temperature distribution depends not only on the velocity ratio parameter of the plate, but also on the power law index and Prandtl number of fluids. [Preview Abstract] |
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JU.00022: The Explanation of the Photon's Electric and Magnetic Fields; and its Particle and Wave Characteristics Russell Moon, Victor Vasiliev Using the principles of the Vortex Theory, the creation of the photon's electric and magnetic components are explained: the condensed region of space is responsible for creating the photon's electric component and its particle effect; its expansion and contraction is responsible for its frequency; its motion through three dimensional space creates a wave in the surrounding space. This wave is responsible for the photon's magnetic component and wave characteristics. The simultaneous expansion and contraction of both the dense region of space that is the photon and the surrounding space it passes through explains why the electric and magnetic effects are at right angles to each other. Also the photon's particle and wave characteristics are explained. 1.Russell Moon, \textit{The Bases of the Vortex Theory of Space}. Publishing house of ZNAK, Moscow, Russia, 2002, 32 pp., (in Russian). 2 R.G. Moon, \textit{The Possible Existence of a New Particle: the Neutral Pentaquark}? Book of materials, The Research Centre of Ecological Safety of the Russian Academy of Sciences: Scientific Seminar 0f Ecology and Space 1, February 22, 2005, Saint-Petersburg, Russia, 2005, pp. 98-104. [Preview Abstract] |
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JU.00023: ABSTRACT WITHDRAWN |
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JU.00024: Lagrangian Properties of Cloud Particles in Turbulence Obtained by Holographic Particle Tracking J.P. Fugal, J. Lu, H. Nordsiek, E.W. Saw, R.A. Shaw We have designed a laboratory system for studying Lagrangian statistics of particles in homogeneous, isotropic turbulence. The system is designed to match the flow and particle conditions governing the collision rate of droplets in atmospheric clouds (e.g., particle Stokes number and gravitational settling parameter). Two methods for particle tracking are used, both based on digital in-line holography. The first is a combination of stereo-imaging and holography using two cameras. The second uses a single holographic system with depth resolution improved by temporal averaging of particle position. These approaches provide a tool for quantifying the 3-D Lagrangian properties of inertial particles with finite settling speed in homogeneous isotropic turbulence. Lagrangian statistics relevant to the cloud coalescence problem are discussed. Acknowledgement: This work has benefited greatly from our collaboration with E. Bodenschatz, L. Collins, and Z. Warhaft through the International Collaboration for Turbulence Research (ICTR). [Preview Abstract] |
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JU.00025: Study of flow and particle distribution in a bifurcation using dynamic NMR Microscopy E.O. Fridjonsson, J.D. Seymour, S.L. Codd, G.R. Cokelet The flow and distribution of Newtonian, polymeric and colloid suspension fluids at low Reynolds numbers in bifurcations has importance in a wide range of disciplines, including microvascular physiology and microfluidic devices. A bifurcation consisting of circular capillaries laser etched in a hard polymer with inlet diameter 2.64 mm, bifurcating to a small diameter outlet of 0.76 mm, and a large outlet of 1.35 mm diameter is examined using four distinct fluids (Water, 0.25 percent (w/w) Xanthan Gum, 8 and 22 percent (v/v) polydisperse oil inside core-shell latex particles) at different flow rates from 5mL/hr to 30mL/hr covering a range of Reynolds numbers based on the entry flow from 0.3 to 8. A Bruker DRX250 NMR system is used with PGSE techniques to obtain dynamic images of the fluids inside the bifurcation. Velocity in all three spatial directions is examined to determine the impact of secondary flows and characterize the transport in the bifurcation. The velocity data provides direct measurement of the volumetric distribution of the flow between the two channels. For the colloidal particle flow the distribution of colloid particles down the capillary is determined by examining the spectrally resolved propagator for the oil inside the core-shell particles in the direction perpendicular to the axial flow. Using dynamic NMR Microscopy the potential for using magnetic resonance for particle counting in a microscale bifurcation is thus demonstrated. [Preview Abstract] |
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JU.00026: A study of thermal turbulent boundary layers over heterogeneous surfaces. Leonardo Chamorro, Rob Stoll, Fernando Porte-Agel, Mehran Parsheh Wind tunnel experiments and large-eddy simulations are performed to investigate the effect of surface temperature transitions on the dynamics of thermally stratified turbulent boundary layers. Particular attention is placed on characterizing the spatial distribution of turbulent fluxes of heat and momentum, and understanding their relation to the velocity and temperature fields. This information is used to test parameterizations of surface fluxes commonly used in weather prediction and air quality models. These parameterizations, based on Monin-Obukhov similarity theory, are found to significantly underestimate the surface heat flux due to their inability to capture the heat flux enhancement associated with advection of relatively warm air over cold surfaces. The wind tunnel measurements and simulation results are also used to develop and test new parameterizations for the average surface fluxes. The new parameterizations are based on local similarity theory and result in substantially improved predictions of the surface fluxes. [Preview Abstract] |
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JU.00027: Lagrangian Investigation of Two-dimensional Decaying Turbulence Michael Wilczek, Oliver Kamps, Rudolf Friedrich We present a numerical investigation of two-dimensional decaying turbulence in the Lagrangian picture. Focusing on single particle statistics, we investigate Lagrangian trajectories in a freely evolving turbulent velocity field. The dynamical evolution of the tracer particles is strongly dominated by the emergence and evolution of coherent structures. For a statistical analysis we focus on the Lagrangian acceleration as a central quantity. We find that the time-resolved acceleration pdf has a highly non-Gaussian functional form with pronounced tails. When normalized by its standard deviation the pdf's of this quantity collapse over a wide temporal range of the decay process, indicating that a self-similar scaling regime can also be found in the Lagrangian frame of reference. In addition to that a decomposition of the acceleration into components parallel and perpendicular to the velocity gives further information about the impact of coherent vortices on the Lagrangian dynamics. [Preview Abstract] |
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JU.00028: Vortex Induced Oscillations of Cylinders at Intermediate Reynolds Numbers Ashwin Vaidya, Roberto Camassa, Bong Jae Chung, Angele Freeman, Philip Howard, Richard McLaughlin The orientational aspect of bodies interacting with fluids is a very fascinating subject. In this study we look at the orientation and dynamics of a hinged cylinder which is immersed in a flow and free to rotate in the direction transverse to the flow. In this presentation, we will systematically discuss our experimental observations on the oscillatory dynamics of the body and the various bifurcations that it undergoes with changing Reynolds numbers and particle inertia. We also hope to be able to discuss the vortex shedding process that gives rise to these oscillations and a three dimensional numerical simulation that is being attempted based on the Chimera grid method using a finite volume scheme. [Preview Abstract] |
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JU.00029: Binary Gas Mixtures of Light Helium to Intensify Laminar Forced Convection in Round Tubes Antonio Campo, Salah Chikh, Mohammad Papari, Mahammad Mobinipouya This paper addresses potential heat transfer enhancement of laminar gaseous flows inside tubes with constant wall temperatures. The goal is to investigate the capabilities of certain binary gas mixtures of light helium as the primary gas with nitrogen, oxygen, carbon dioxide, methane, sulfur hexafluoride and tetrafluoromethane as the secondary heavier gases. The velocity of the binary gas mixtures is fully established and the temperature develops from a uniform value. The thermophysical properties of the binary gas mixtures depend on the molar gas composition in the w-domain [0, 1]. The two case studies involve a low mean bulk temperature of 300 K and the other a high mean bulk temperature of 600 K, both sharing 1 atm. The two target parameters for analysis and design are the maximum heat transfer rate and the pressure drop at the optimal molar gas composition. [Preview Abstract] |
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JU.00030: Detection of the Electromagnetic Field Induced by the Wake of a Ship Moving in a Random Sea of Finite Depth Oded Yaakobi, Gregory Zilman, Touvia Miloh The purpose of this work is to examine the feasibility to detect an ocean going vessel by its wake in the presence of wind waves. The wake of a ship and the ambient sea waves generate velocity field of electrically conductive seawater. Consequently a disturbance in the Earth geomagnetic field is induced. A closed-form solution for the magnetic field induced by the wake of a ship moving in a sea of finite depth is obtained, and the corresponding numerical simulations are performed. The results of the simulations are compared with the corresponding magnetic field disturbed by wind waves. Spectral analysis of the magnetic field, induced by the wake of a ship and sampled by an air-borne magnetometer moving steadily along a rectilinear path is performed. Numerical computations indicate that the spectra of the magnetic fields induced by the ambient random waves and by the wake of a moving body have quite different characteristic. Typically, the peaks of the body-induced magnetic field spectra are located in the range of frequencies where the corresponding values of the wind wave's spectra are less significant. It is shown that the feasibility of electromagnetic detection of ships wake depends on their speed and water depth. [Preview Abstract] |
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JU.00031: Dynamic pore-level modeling of multi-phase displacement processes in noncircular capillary tubes using a particle-based method Saeed Ovaysi, Mohammad Piri We present a fully dynamic particle-based model of incompressible two-phase flow in capillary tubes with angular cross section. Two-phase drainage and imbibition processes are simulated and the effects of wettability are also studied. The model takes into account viscous pressure drop in both invading and defending phases in addition to the capillary and gravity forces. It uses novel methods to handle particle inconsistencies and wetting strength of fluids. A fully parallel version of the model is used to simulate unsteady-state two-phase (oil and water) processes. The results for the capillary dominated limit are then compared against the values predicted using the MS-P theory. Hydraulic conductivity of fully saturated tubes are computed and compared against the available data in the literature. Dynamic effects are also discussed and it is shown that results for the dynamic system deviate from the MS-P limit. The success of this method in simulating multi-phase displacement processes in noncircular capillary elements provides the platform upon which multi-phase flow problems in highly irregular porous systems (encountered, for instance, in underground oil reservoirs) can be simulated. [Preview Abstract] |
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JU.00032: Flow Pattern within Cubical Arrays of Obstacles - Water Channel Results Marko Princevac, Hansheng Pan, Xiangyi Li, Michael Brown Flows within simple 3 by 3 and 5 by 5 cubical arrays were studied. A Particle Image Velocimetry (PIV) system was used for comprehensive flow measurements in the laboratory for Environmental Flow Modeling at the University of California, Riverside. The obstacles were reproduced using acrylic blocks whose refraction index is the same as the refraction index of salty water. Such setup allowed for laser sheet illumination through the obstacles enabling detailed measurements between the cubes. This is the first time that such detailed measurements of the flow between the obstacles were performed. A flow channeling at right angles to the incoming flow direction was noted. This novel flow feature, lateral channeling, observed and quantitatively measured within the array of cubes will be presented and discussed. The sideways channeling becomes less pronounced as array size increases which may be the reason why this phenomenon was not reported in the past. The sideways channeling becomes more intense when the mid-array cube is higher. This lateral flow channeling may be accountable for a significant initial plume spread observed when the plume encounters an urban area. The pattern was reproduced by k-e model. [Preview Abstract] |
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JU.00033: Phase Field Model of Contact Angle Hysteresis Mahesh Panchagnula, Srikanth Vedantam We describe a phase field theory based model in the Ginzburg-Landau framework for wetting of surfaces by sessile drops. The theory uses a two dimensional non-conserved phase field variable to parametrize the Gibbs free energy of the three dimensional system. Contact line tension is included through the gradient term in the free energy and contact angle hysteresis arises out of a special form of the kinetic coefficient. The form of the kinetic co-efficient is chosen to include both rate dependent as well as rate independent effects on contact angle hysteresis. In this fashion, hysteresis is included constitutively without explicit consideration of the underlying causes. We invoke a spherical cap approximation for the shape of most of the drop for the reduced order of dimensionality. Using this theory we examine the wetting of a surface containing a circular heterogeneous island. The model captures the empirically observed contact angle behavior and is found to be determined solely by the material properties at the contact line. [Preview Abstract] |
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JU.00034: Vortex Shedding behind an Airfoil: Where the Particles Come From Blake Cardwell, Kamran Mohseni Intensifying interest in flow actuation during flight is driving the quest of understanding vortex shedding flow structure. In support of this goal, fundamental questions regarding particle behavior must be answered. One such question is where the particles that make up a shed vortex pair come from, and how do they form into the recognizable shape now well known to fluid dynamisits. To answer this question, the distinctive regions of particle mixing which make up the vortex shape have been identified and advected backwards in time to understand how a vortex forms. [Preview Abstract] |
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JU.00035: Simulation of bio-locomotion by a momentum redistribution technique for self-propulsion Oscar Curet, Anup Shirgaonkar, Neelesh Patankar, Malcolm MacIver We have developed a general purpose computational approach for self-propulsion based on a momentum redistribution concept. In this poster, our primary goal is to show that the technique can simulate swimming of various organisms without using reduced order models for fluid dynamics. The approach fully resolves the motion of the organism and the surrounding fluid. Thus, it is an effective tool to obtain forces, flow fields, as well as the swimming velocity when the deformation kinematics of the organism are available from observational data. We will present images of computational flow fields for several examples including the aquatic locomotion of sperm, jellyfish, eel, and blackghost knifefish. These examples span a range of body configurations, swimming gaits, and Reynolds numbers in their natural environments. Peculiarities of various modes of swimming will be highlighted. [Preview Abstract] |
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