Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session G23: General Fluids I |
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Chair: Patrick Weidman, University of Colorado Room: 30D |
Monday, November 19, 2012 8:00AM - 8:13AM |
G23.00001: Obliquely-intersecting Hiemenz stagnation-point flows Patrick Weidman The interaction of two obliquely-intersecting Hiemenz stagnation point flows normal to a flat plate is studied. One flow of strain rate a aligned along the x-axis intersects the other of strain rate b at angle Phi from the x-axis. When transformed to principal axes, a similarity reduction of the Navier-Stokes equation yields two ordinary differential equations with coefficients depending on the strain rate ratio Sigma = b/a and Phi. These equations are then tranformed to Howarth's equations via a two-parameter mapping. The large-Sigma asymptotic behavior of solutions for the limiting angles Phi = 0 and 90 deg. are determined. Numerical solutions of the principal axes equations for values of Sigma in the saddle-point and nodal-point regions at Phi = 0, 15, 30, 45, 60, 75 and 90 deg. compare precisely with those obtained from the two-parameter mapping. Plots of the wall shear stress parameters, the normalized displacement thicknesses and sample velocity profiles are presented. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G23.00002: A numerical study of the motion of a neutrally buoyant cylinder in two dimensional shear flow Tsorng-Whay Pan, Shih-Lin Huang, Shih-Di Chen, Chin-Chou Chu, Chien-Cheng Chang We have investigated the motion of a neutrally buoyant cylinder of circular or elliptic shape in two dimensional shear flow of a Newtonian fluid by direct numerical simulation. The numerical results are validated by comparisons with existing theoretical, experimental and numerical results, including a power law of the normalized angular speed versus the particle Reynolds number. The centerline between two walls is an expected equilibrium position of the cylinder mass center in shear flow. When placing the particle away from the centerline initially, it migrates toward another equilibrium position for higher Reynolds numbers due to the interplay between the slip velocity, the Magnus force, and the wall repulsion force. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G23.00003: An analysis of the ``accidental painting'' technique of D.A. Siqueiros: the Rayleigh Taylor instability as a tool to create explosive textures S. Zetina, R. Zenit In the spring of 1936, the famous Mexican muralist David Alfaro Siqueiros organized an experimental painting workshop in New York: a group of artists focused in developing painting techniques through empirical experimentation of modern and industrial materials and tools. Among the young artists attending the workshop was Jackson Pollock. They tested different lacquers and a number of experimental techniques. One of the techniques, named by Siqueiros as a ``controlled accident,'' consisted in pouring layers of paint of different colors on top of each other. After a brief time, the paint from the lower layer emerged from bottom to top creating a relatively regular pattern of blobs. This technique led to the creation of explosion-inspired textures and catastrophic images. We conducted an analysis of this process. We experimentally reproduced the patterns ``discovered'' by Siquieros and analyzed the behavior of the flow. We found that the flow is driven by the well-known Rayleigh Taylor instability: different colors paints have different densities; a heavy layer on top of a light one is an unstable configuration. The blobs and plumes that result from the instability create the aesthetically pleasing patterns. We discuss the importance of fluid mechanics in artistic creation. [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G23.00004: Data Reduction Modeling of a Graphite Nitridation Experiment Paul Bauman, Robert Moser In this work, we present a computational study of a flow tube experiment in order to infer reaction parameters for graphite nitridation. This study builds off previous work where it was determined existing, simplified models were inadequate to meaningfully inform parameters of the nitridation reaction of interest. We construct a two-dimensional representation of the experimental setup and model the flow using a reacting low-Mach number approximation to the Navier-Stokes equations. We use a stabilized finite element method to approximate the mathematical model. To solve the inverse problem for the reacting parameters, we employ a Bayesian approach in order to produce probability distributions that can used to quantify uncertainty in models where surface nitridation is important. Such models include the surface ablation of thermal protection systems of reentry vehicles. [Preview Abstract] |
Monday, November 19, 2012 8:52AM - 9:05AM |
G23.00005: Fluid flow and ponding on elastic beams Jerome Neufeld, Rachael Bonnebaigt Fluids propagate over floating, elastically deformable surfaces in a variety of industrial, environmental, and geological settings, and can exhibit a wide variety of transient and steady-state behaviours. Here we show that, for a sufficiently localised release, steady states exist where a dense, viscous fluid propagates along a beam floating on a relatively light, inviscid ocean. The steady-state radius, fluid depth, and elastic deformation can be characterised solely as functions of the beam's bending length scale, and the relative densities of ocean and fluid. In contrast, for releasees of relatively light fluid no steady states exist, and a transient solution is instead found. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G23.00006: Void collapse under distributed dynamic loading near material interfaces Galina Shpuntova, Joanna Austin Collapsing voids cause significant damage in diverse applications from biomedicine to underwater propulsion to explosives. While shock-induced void collapse has been studied extensively, less attention has been devoted to stress wave loading, which will occur instead if there are mechanisms for wave attenuation or if the impact velocity is relatively low. A set of dynamic experiments was carried out in a model experimental setup to investigate the effect of acoustic heterogeneities in the surrounding medium on void collapse. Two tissue-surrogate polymer materials of varying acoustic properties were used to create flowfield geometries involving a boundary and a void. A stress wave, generated by projectile impact, triggered void collapse in the gelatinous polymer medium. When the length scales of features in the flow field were on the same order of magnitude as the stress wave length scale, the presence of the boundary was found to affect the void collapse process relative to collapse in the absence of a boundary. This effect was quantified for a range of geometries and impact conditions using a two-color, single-frame particle image velocimetry technique. [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G23.00007: Fog-harvesting Mesh Surfaces Kyoo-Chul Park, Shreerang S. Chhatre, Siddarth Srinivasan, Robert E. Cohen, Gareth H. McKinley Fog represents a large, untapped source of potable water, especially in arid climates. Various plants and animals use morphological as well as chemical features on their surfaces to harvest this precious resource. In this work, we investigate the influence of surface wettability, structural length scale, and relative openness of the weave on the fog harvesting ability of mesh surfaces. We choose simple woven meshes as a canonical family of model permeable surfaces due to the ability to systematically vary periodicity, porosity, mechanical robustness and ease of fabrication. We measure the fog collecting capacity of a set of meshes with a directed aqueous aerosol stream to simulate a natural foggy environment. Further, we strive to develop and test appropriate scalings and correlations that quantify the collection of water on the mesh surfaces. These design rules can be deployed as an a priori design chart for designing optimal performance meshes for given environmental/operating conditions. [Preview Abstract] |
Monday, November 19, 2012 9:31AM - 9:44AM |
G23.00008: Inertial Lubrication Theory Mederic Argentina, Nicolas Rojas, Enrique Cerda, Enrique Tirapegui Thin fluid films can have surprising behavior depending on the boundary conditions enforced, the energy input and the specific Reynolds number of the fluid motion. Here we study the equations of motion for a thin fluid film with a free boundary and its other interface in contact with a solid wall. Although shear dissipation increases for thinner layers and the motion can generally be described in the limit as viscous, inertial modes can always be excited for a sufficiently high input of energy. We derive the minimal set of equations containing inertial effects in this strongly dissipative regime. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G23.00009: An Experimental Study of Soft Lubrication Qianhong Wu, Thomas Gacka, Rungun Nathan, Li-Zhu Wu Lift generation in soft porous media, as a planing surface glides over it, is a new topic in porous media flow with superior potential for lubrication and squeeze damping. This paper presents the first experimental study of this phenomenon. The experimental setup consists of a running conveyer belt covered with a soft porous sheet, and a stationary instrumented inclined planar upper board. Twelve pressure transducers mounted on the upper board captured the pore pressure generation, while a load cell was used to capture the total lifting force, arising from both the pore pressure and the compression of the solid fibers. One finds that the pore pressure distribution is consistent with theoretical predictions (Feng and Weinbaum, JFM, 2000; Wu et al., MSSE, 2006, 2011), and depends on the running belt velocity, U, the mechanical properties of the porous material, and the compression ratios of the porous layer. For a typical trial (h$_{2}$/h$_{1}$=5,h$_{2}$/h$_{0}$=1, U=3.8 m/s, where h$_{2}$, h$_{1}$, and h$_{0}$ are the leading edge, trailing edge, and undeformed porous layer thicknesses, respectively), 68{\%} of the lifting force was generated by the pore pressure. It conclusively demonstrates the validity of using soft porous materials for super lubrication. applications. [Preview Abstract] |
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