Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session M22: General Fluid Dynamics IIGeneral
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Chair: Aline Cotel, University of Michigan Room: 708 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M22.00001: Experimental study of snow friction Caroline Cohen, Luca Canale, Alessandro Siria, David Quere, Lyderic Bocquet, Christophe Clanet Snow friction results from the interplay of different physical processes: solid friction of granular material, phase change and lubrication, heat transport, capillarity, elasticity and plasticity. The multiple conditions of temperature, humidity and density of the snow result in different regimes of friction. In particular, there is an optimal amount of melted water to lubricate the contact between the ski sole and the snow grains. The thickness of the water layer depends on temperature, speed... A huge variety of waxes have been empirically developed to adapt the amount of water to the conditions of skiing, but remain mysterious. In these study, we investigate experimentally the mechanisms of snow friction at different scales: first, the friction of a ski on snow is measured on a test bench, depending on the snow characteristics and for different waxes. Then microscopic experiments are led in order to understand the friction at the ice crystals scale. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M22.00002: An Experimental and numerical Study for squeezing flow Rungun Nathan, Ji Lang, Qianhong Wu We report an experimental and numerical study to examine the transient squeezing flow driven by sudden external impacts. The phenomenon is widely observed in industrial applications, e.g. squeeze dampers, or in biological systems, i.e. joints lubrication. However, there is a lack of investigation that captures the transient flow feature during the process. An experimental setup was developed that contains a piston instrumented with a laser displacement sensor and a pressure transducer. The heavy piston was released from rest, creating a fast compaction on the thin fluid gap underneath. The motion of the piston and the fluid pressure build-up was recorded. For this dynamic process, a CFD simulation was performed which shows excellent agreement with the experimental data. Both the numerical and experimental results show that, the squeezing flow starts with the inviscid limit when the viscous fluid effect has no time to appear, and thereafter becomes 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. The study presented herein, filling the gap in the literature, will have broad impacts in industrial and biomedical applications. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M22.00003: Model of a Soft Robotic Actuator with Embedded Fluidic Network Benny Gamus, Yizhar Or, Amir Gat Soft robotics is an emerging bio-inspired concept of actuation, with promising applications for robotic locomotion and manipulation. Focusing on actuation by pressurized embedded fluidic networks, we present analytic formulation and closed-form solutions of an elastic actuator with pressurized fluidic networks. In this work we account for the effects of solid inertia and elasticity, as well as fluid viscosity, which allows modelling the system's step-response and frequency response as well as suggesting mode elimination and isolation techniques. We also present and model the application of viscous-peeling as an actuation mechanism, simplifying the fabrication process by eliminating the need for internal cavities. The theoretical results describing the viscous-elastic-inertial dynamics of the actuator are illustrated by experiments. The approach presented in this work may pave the way for the design and implementation of soft robotic legged locomotion that exploits dynamic effects. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M22.00004: The Zig-zag Instability of Streamlined Bodies Thibault Guillet, Martin Coux, David Quere, Christophe Clanet When a floating bluff body, like a sphere, impacts water with a vertical velocity, its trajectory is straight and the depth of its dive increases with its initial velocity. Even though we observe the same phenomenon at low impact speed for axisymmetric streamlined bodies, the trajectory is found to deviate from the vertical when the velocity overcomes a critical value. This instability results from a competition between the destabilizing torque of the lift and the stabilizing torque of the Archimede's force. Balancing these torques yields a prediction on the critical velocity above which the instability appears. This theoretical value is found to depend on the position of the gravity center of the projectile and predicts with a full agreement the behaviour observed in our different experiments. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M22.00005: A laboratory investigation of mixing dynamics between biofuels and surface waters Xiaoxiang Wang, Aline Cotel Recently, production and usage of ethanol-blend fuels or biofuels have increased dramatically along with increasing risk of spilling into surface waters. Lack of understanding of the environmental impacts and absence of standard clean-up procedures make it crucial to study the mixing behavior between biofuels and water. Biofuels are represented by a solution of ethanol and glycol. A Plexiglas tank in conjunction with a wave generator is used to simulate the mixing of surface waters and biofuels under different natural conditions. In our previous experiments, two distinct mixing regimes were observed. One regime was driven by turbulence and the other by interfacial instabilities. However, under more realistic situations, without wind driven waves, only the first mixing regime was found. After one minute of rapid turbulent mixing, biofuels and water were fully mixed and no interface was formed. During the mixing process, chemical reactions happened simultaneously and influenced mixing dynamics. Current experiments are investigating the effect of waves on the mixing dynamics. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M22.00006: Fluid Mixing in the Eye Under Rapid Eye Movement Jinglin Huang, Morteza Gharib Drug injection is an important technique in certain treatments of eye diseases. The efficacy of chemical mixing plays an important role in determining pharmacokinetics of injected drugs. In this study, we build a device to study the chemical mixing behavior in a spherical structure. The mixing process is visualized and analyzed qualitatively. We hope to understand the chemical convection and diffusion behaviors in correlation with controlled rapid mechanical movements. The results will have potential applications in treatment of eye diseases. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M22.00007: Pressure Field Estimates in a Three-Dimensional Turbulent Wall Jet Adam Nickels, Lawrence Ukeiley, Robert Reger, Louis Cattafesta Low-order estimates of turbulent velocity fields are useful for understanding large-scale motions in turbulent flows. The use of these estimates for the calculation of coupled quantities such as the hydrodynamic pressure however has not been fully evaluated in terms of the quantitative features that are reproduced in many three-dimensional flows. In this work, 16 individual spanwise aligned particle image velocimetry measurement planes of an aspect ratio 8 wall jet are independently obtained, synchronously with 32 surface pressure transducer measurements. An estimate of the three-dimensional velocity field is calculated via modified stochastic estimation and used to solve Poisson's equation for pressure fluctuations throughout the measurement ``volume.'' The large scale vortical motion captured by the velocity estimates result in convecting, intermittent positive and negative pressure regions throughout the wall jet. The estimated surface pressure spectrum captures similar features as the measurements in the most energetic portion of the spectrum and matches measured spectral magnitudes well in the region impacted by the breakdown of the jet core where the near wall region is impacted by the large scale motion. Knowledge of the pressure field also allows for the calculation of pressure related terms from the Reynolds stress transport equation, which can be of use in the construction of turbulence models. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M22.00008: Fine structure symmetry-breaking in decaying passive scalars advected by laminar shear flow Francesca Bernardi, Manuchehr Aminian, Roberto Camassa, Daniel Harris, Richard McLaughlin We investigate the dispersion of a passive scalar in laminar shear flow through rectangular and elliptical channels. We show through simulation, analysis and experiments that the cross-sectional aspect ratio sets the sign of the average skewness at long times, which describes the longitudinal asymmetry of the tracer distribution. We then extend the results to study the entire tracer distribution rather than only its longitudinal moments. With an analytical approach, we show that it is possible to describe the behavior of the tracer distribution at long time at any location in the cross-section, in turn highlighting the mechanism by which symmetry is broken. Future directions will be discussed. [Preview Abstract] |
(Author Not Attending)
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M22.00009: Stochastic Modeling of Super-Dispersion in Chaotic Flows Ehsan Kharazmi, Mohsen Zayernouri, Farhad A. Jaberi Experimental studies have revealed that the statistical distributions of turbulent variables, even in canonical flows, are often strongly non-Gaussian, asymmetric, heavy-tailed, and sometimes involve sharp peaks. Examples of such anomalies are observed in grid turbulence, atmospheric boundary layers, and dispersion of particles in shear layers. We propose a stochastic distributed-order model for the enhanced dispersion of passive particles in the context of shear layers and an array of planar jets. We establish a physical and statistical link between the power-law behavior obtained for the mean square of particles displacement, in addition to mean square of velocity and vorticity increments to the cascade of turbulent kinetic energy. [Preview Abstract] |
Tuesday, November 21, 2017 9:57AM - 10:10AM |
M22.00010: Electromagnetic Wave Transmittance Control using Anisotropic Plasma Lattice Eric Matlis, Thomas Corke, Anthony Hoffman Experiments of transmission through a lattice array of plasma columns have shown an absorption band close to the plasma frequency at 14 GHz. The beam was oriented at a 35$^{\circ}$ incident angle to the planar plasma cell. These experiments were designed to determine if the observed absorption was the result of the isotropic plasma medium or that of an anisotropic metamaterial. Transmission of the microwave energy was not consistent with an isotropic material in which absorption would monotonically increase below the plasma frequency. The experimental results are supported by an anisotropic model which was developed for the plasma permittivity using an effective medium approximation. The plasma columns were modeled as uniform rods with permittivity described by a Drude model while the components of the permittivity tensor was calculated using the Maxwell-Garnett effective medium theory. Electron densities of $n=4x10^{12} cm^{-3}$ were assumed which is consistent with prior experimental measurements. This model confirms the existence of non-zero imaginary wave vector $k$ in a narrow region centered about 14 GHz. [Preview Abstract] |
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