Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H9: General Fluid Dynamics |
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Chair: Thomas Corke, University of Notre Dame Room: B117 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H9.00001: Biofuels spills in surface waters – a laboratory investigation of mixing and interfacial dynamics Xiaoxiang Wang, Aline Cotel There are increasing risks of spills of ethanol-based biofuels in aquatic environments, however the environmental impact of such accidents is poorly understood and no adequate mitigation strategies are in place today. The interaction of water and biofuels is a complex dynamical problem and we aim to quantify the physical processes involved in such dynamics. A solution of ethanol and glycol is used to represent a typical ethanol-based fuel. A small-scale Plexiglas tank has been designed to investigate the effect of natural conditions on the mixing of water and biofuels, e.g. slope angle, flow rate, wave amplitude and frequency in wind driven conditions. Our previous work showed that the existence of two distinct mixing regimes; a first turbulence-driven fast mixing regime and a second regime driven by interface instabilities. We investigate these mixing regimes under an extended range of physical parameters representing more natural configurations. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H9.00002: Hydrodynamical force on a solid sphere in an incompressible inviscid fluid Rabab AlArki, D. Palaniappan Simple analytic results for the hydrodynamical force exerted on a rigid sphere of radius $a$ placed in singularity driven potential flows are determined. The motion induced singularities considered are (i) a source; (ii) a dipole; and (iii) a vortex ring, located at $(0,0,c)$, where $c>a$. The calculation is based on the exact solutions of the classical Neummann boundary value problem for a spherical boundary in inviscid hydrodynamics. The expressions for the force due to source and dipole are found to be algebraic in a/c, the radius-location ratio, while the result for a vortex ring is expressed in an integral form. Our analysis shows that the force due to a tangentially oriented initial dipole is less than that of a dipole in the radial direction. Graphical illustration are presented demonstrating the variation of the force with respect to a/c. The results may also be of intersect in the study of superfluids - treated as incompressible fluids - such as liquid helium or the interior of a neutron star. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H9.00003: Numerical investigation on fluid flow past transversely oscillating vertical rectangular cylinder Jeevananthan Kannan, Arul Prakash K In the present study, the rectangular cylinder was forced to vibrate for various flow configurations such as the AR (Aspect Ratio) ranging from 0.2 to 1 and Reynolds number based on (depth of the cylinder) as 100, 150, 200. The frequency ratio (excitation frequency, fe / natural shedding frequency, fns) chosen for the study was 0.5, 0.75, 1.0, 1.5 and 2.0. The vibrating amplitude 0.1, 0.2 and 0.3 of cylinder depth were also considered. For the slender aspect ratios (AR\textless 1), the flow phenomena becomes more complex, due to the short vortex formation length. The separated shear layers were incessantly swiveling behind the cylinder dispense the vortices in the downstream of the wake as inline shedding packets. Three dimensional Studies are also established for the selected cases. The influence of the cylinder vibration on the wake patterns, phase plane, lift, drag force etc. are presented and discussed. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H9.00004: A Numerical Simulation of the Density Oscilator Sergio Hernandez Zapata, Erick Javier Lopez Sanchez, Gerardo Ruiz Chavarria In this work we carry out a numerical simulation for the dynamics that originates when a fluid (salty water) is located on top of another less dense fluid (pure water) in the presence of gravity. This is an unstable situation that leads to the development of intercalating lines of descending salty water and ascending pure water. Another situation is studied where the fluids are in two containers joined by a small hole. In this case a time pattern of alternating flows develops leading to an oscillator. The study of the velocity field around the hole shows than in a certain interval of time it develops intercalating lines like in the former situation. An interesting result is the fact that when a given fluid is flowing in one direction a vorticity pattern develops in the other fluid. The Navier-Stokes, continuity and salt diffusion equations, are solved numerically in cylindrical coordinates, using a finite difference scheme in the axial and radial directions and a Fourier spectral method for the angular coordinate. On the other hand, the second order Adams-Bashfort method is used for the time evolution. The results are compared to a numerical simulation of a pedestrian oscillator we developed based on the Hebling and Molnar social force model. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H9.00005: Decalcomania Bernardo Palacios, Sandra Zetina, Roberto Zenit Decalcomania is a painting technique, used by many abstract painters such as Max Ernst and Remedios Varo, which is used to create striated textures of unique aesthetic appeal. A decalcomania consists of separating two flexible sheets, between which fluid paint had been placed. As the flexible sheets are detached and the paint retracts from its original edge, finger-like striae are formed. The technique holds a certain similarity to that used to test adhesive materials and to the Saffman-Taylor instability. To fully understand the process, we recreate it in a controlled manner. We used an experimental setup consisting of two transparency sheets, which separate angularly from each at a controlled rate. The process is filmed with a high-speed camera. The separation speed and fluid properties are varied, to determine their effect on the pattern formation and the produced texture. We present and discuss preliminary results of this study. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H9.00006: The Effects of Outer Flow Conditions on the Emergence and Evolution of Geometrical Self Similarity of a Bluff Body during Ablation Michael Allard, Christopher M White The ablation process (i.e., erosion) of a bluff body, low-temperature ablator is investigated. Two experimental configurations in a heated open-circuit thermal boundary layer wind tunnel are considered: (a) the bluff body is supported in the free stream or (b) placed within the boundary layer growing on the bottom wall of the tunnel. These two configurations were chosen to investigate the effects of outer flow conditions (i.e. uniform in the free stream and varying with the boundary layer) on the emergence and evolution of geometrical self similarity during ablation. A time sequence of streamwise-transverse and streamwise-wall normal images were recorded. The images were analyzed to investigate the temporal evolution of the bluff body's projected area, perimeter, and curvature. The results were compared to similar studies where the erosion was caused from fluid shear force and chemical dissolution both of which scaled-similarly. The insights gained from this study can be used to progress towards physics-based models of bluff body ablation. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H9.00007: Latent heat of vehicular motion Farzad Ahmadi, Austin Berrier, Mohammad Habibi, Jonathan Boreyko We have used the thermodynamic concept of latent heat, where a system loses energy due to a solid-to-liquid phase transition, to study the flow of a group of vehicles moving from rest. During traffic flow, drivers keep a large distance from the car in front of them to ensure safe driving. When a group of cars comes to a stop, for example at a red light, drivers voluntarily induce a "phase transition" from this "liquid phase" to a close-packed "solid phase." This phase transition is motivated by the intuition that maximizing displacement before stopping will minimize the overall travel time. To test the effects of latent heat on flow efficiency, a drone captured the dynamics of cars flowing through an intersection on a Smart Road where the initial spacing between cars at the red light was systematically varied. By correlating the experimental results with the Optimal Velocity Model (OVM), we find that the convention of inducing phase transitions at intersections offers no benefit, as the lag time (latent heat) of resumed flow offsets the initial increase in displacement. These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to maximize safety with no loss in flow efficiency. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H9.00008: Large-aperture Tunable Plasma Meta-material to Interact with Electromagnetic Waves Thomas Corke, Eric Matlis The formation of spatially periodic arrangements of glow discharge plasma resulting from charge instabilities were investigated as a tuneable plasma meta-material. The plasma was formed between two 2-D parallel dielectric covered electrodes: one consisting of an Indium-Tin-Oxide coated glass sheet, and the other consisting of a glass-covered circular electrode. The dielectric covered electrodes were separated by a gap that formed a 2-D channel. The gap spacing was adjustable. The electrodes were powered by a variable amplitude AC generator. The parallel electrode arrangement was placed in a variable pressure vacuum chamber. Various combinations of gap spacing, pressure and voltage resulted in the formation of spatially periodic arrangements (lattice) of glow discharge plasma. The lattice spacing perfectly followed 2-D packing theory, and was fully adjustable through the three governing parameters. Lattice arrangements were designed to interact with electromagnetic (EM) waves in the frequency range between 10GHz-80GHz. Its feasibility was investigate through an EM wave simulation that we adapted to allow for plasma permittivity. The results showed a clear suppression of the EM wave amplitude through the plasma gratings. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H9.00009: Fluid Shearing for Accelerated Chemical Reactions - Fluid Mechanics in the VFD Evgenia Leivadarou, Stuart Dalziel The Vortex Fluidic Device (VFD) is a rapidly rotating tube that can operate under continuous flow with a jet feeding liquid reactants to the tube's hemispherical base. It is a new `green' approach to the organic synthesis with many industrial applications in cosmetics, protein folding and pharmaceutical production. The rate of reaction in the VFD is enhanced when the collision rate is increased. The aim of the project is to explain the fluid mechanics and optimize the performance of the device. One contribution to the increased yield is believed to be the high levels of shear stress. We attempt to enhance the shear stress by achieving high velocity gradients in the boundary layers. Another factor is the uncontrolled vibrations due to imperfections in the bearings and therefore it is important to assess their influence in the initial spreading. The surface area of the film should be maximized with respect to the rotation rate, geometry and orientation of the tube, flow rate, wettability and contact line dynamics. Experiments are presented for a flat disk and a curved bowl, establishing the optimum height of release, rotation rate and tube orientation. Vibrations were imposed to investigate the changes in the film formation. We discuss the implications of our results in the VFD. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H9.00010: A Theoretical and Experimental Study for a Developing Flow in a Thin Fluid Gap Qianhong Wu, Ji Lang, Kei-peng Jen, Rungun Nathan In this paper, we report a novel theoretical and experimental approach to examine a fast developing flow in a thin fluid gap. Although the phenomena are widely observed in industrial applications and biological systems, there is a lack of analytical approach that captures the instantaneous fluid response to a sudden impact. An experimental setup was developed that contains a piston instrumented with a laser displacement sensor and a pressure transducer. A sudden impact was imposed on the piston, creating a fast compaction on the thin fluid gap underneath. The motion of the piston was captured by the laser displacement sensor, and the fluid pressure build-up and relaxation was recorded by the pressure transducer. For this dynamic process, a novel analytical approach was developed. It starts with the inviscid limit when the viscous fluid effect has no time to appear. This short process is followed by a developing flow, in which the inviscid core flow region decreases and the viscous wall region increases until the entire fluid gap is filled with viscous fluid flow. A boundary layer integral method is used during the process. Lastly, the flow is completely viscous dominant featured by a typical squeeze flow in a thin gap. Excellent agreement between the theory and the experiment was achieved. The study presented herein, filling the gap in the literature, will have broad impact in industrial and biomedical applications. [Preview Abstract] |
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