Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D4: Compressible Flows: Shocks |
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Chair: Lawrence Ukeiley Ukeiley, University of Florida Room: 103 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D4.00001: Numerical and Experimental Investigation of Oblique Shock Wave Reflection from a Water Wedge Qian Wan, Hongjoo Jeon, Veronica Eliasson Shock wave interaction with solid wedges at different inclination angles has been an area of much research studied in the past, but not many results have been obtained for shock wave reflection from liquid wedges. To find the transition angle from regular to irregular reflection of shock wave reflection over liquid wedges - both Newtonian and non-Newtonian liquids - we used a combination of experimental and numerical methods. In experiments, an inclined shock tube with adjustable inclination angle and a test section filled with the liquid of interest was used. Simulations were performed using a collection of CFD and CSD solvers to simulate the same situation as in the experiments. Results show that the transition angles for liquid wedges is different from smooth solid wedges, but agree fairly well if one assumes a certain surface roughness of the solid wedge. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D4.00002: Measurements of Transient Phenomena in a Shock Tube using Pulse-Burst PIV Justin Wagner, Steven Beresh, Edward DeMauro, Brian Pruett, Paul Farias Time-resolved particle image velocimetry (TR-PIV) measurements are made in a shock tube using a pulse-burst laser. Two transient flowfields are investigated including the baseline flow in the empty shock tube and the wake growth downstream of a cylinder spanning the width of the test section. Boundary layer growth is observed following the passage of the incident shock in the baseline flow, while the core flow velocity increases with time. Comparison of this measured core flow acceleration to that predicted using classical unsteady boundary layer growth models shows good agreement in some instances. As a result of wall boundary layers, a significant amount of spatial non-uniformity remains in the flow following the passage of the end-wall reflected shock. In the transient wake growth measurements, the wake downstream of the cylinder is symmetric immediately following the passage of the incident shock. At later times, the wake transitions to von Karman vortex shedding. The TR-PIV data are bandpass filtered about the vortex shedding frequency and its harmonics to reveal additional details on the transient wake growth. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D4.00003: Kinematical Compatibility Conditions for Vorticity Across Shock Waves Roy Baty This work develops the general kinematical compatibility conditions for vorticity across arbitrary shock waves in compressible, inviscid fluids. The vorticity compatibility conditions are derived from the curl of the momentum equation using singular distributions defined on two-dimensional shock wave surfaces embedded in three-dimensional flow fields. The singular distributions are represented as generalized differential operators concentrated on moving shock wave surfaces. The derivation of the compatibility conditions for vorticity requires the application of second-order generalized derivatives and elementary tensor algebra. The well-known vorticity jump conditions across a shock wave are then shown to follow from the general kinematical compatibility conditions for vorticity by expressing the flow field velocity in vectorial components normal and tangential to a shock surface. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D4.00004: Passive Shock Wave Attenuation by Liquid Sheets Hongjoo Jeon, Nicholas Amen, Veronica Eliasson The use of liquid sheets to understand passive shock wave attenuation was investigated experimentally by impacting planar liquid sheets of varying thicknesses with planar shock waves. To create a sheet of liquid, a liquid container was designed to hold liquid in the desired shape with 5, 10, and 20 mm thickness in the test section of a shock tube. Planar shock waves with shock Mach numbers ranging from $M_{s} =$ 1.1 to 1.5 were generated. In addition to varying the shock Mach number, different liquid media, water and a cornstarch suspension, were used. Pressure traces show that stronger incident shock waves result in higher reflected and transmitted pressures and that a thicker sheet reduces transmitted pressure but increases reflected pressure. Furthermore, for water versus cornstarch suspensions, a different thickness threshold was found to determine whether the transmitted wave is a shock wave or a pressure wave. Also, the breakup of the liquid sheets was fundamentally different between the two liquids. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D4.00005: Mitigating Shock Waves Using Solid Obstacles with Semi-Circular Grooves Nicholas Amen, Arturo Cajal, Veronica Eliasson An experimental investigation was performed to assess the effectiveness of multiple obstacles with semi-circular grooves placed along a logarithmic spiral curve as a method to attenuate a shock wave. Previous research has shown that the use of multiple obstacles arranged in a log spiral configuration can attenuate a shock wave by reducing the energy of the wave. In this study, four different obstacle cross-sections in the same log spiral configuration were considered. All spirals had square cross-sections with zero, one, two, or three semi-circular grooves in each face. They were placed inside a shock tube where the incident, reflected, and transmitted shocks were visualized with high-speed schlieren imaging and the pressure histories were recorded with four pressure transducers. Each case was studied varying shock Mach numbers between M$=$1.1 and M$=$1.5. The pressure traces were used to establish incident, reflected, and transmitted shock strength and wave speed. Results for the zero groove case were compared to that of the one, two, and three groove cross-sections which show that increasing the number of grooves has a profound effect on the generation of the reflected wave and impacts the transmitted wave via vortex generation behind the spiral. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D4.00006: Effect of initial perturbation amplitude on Richtmyer-Meshkov flows induced by strong shocks Zachary Dell, Robert Stellingwerf, Snezhana Abarzhi We study the effect initial perturbation on the Richtmyer-Meshkov (RM) flows induced by strong shocks in fluids with contrasting densities. Smooth Particle Hydrodynamics simulations are employed. Broad range of shock strengths and density ratios is considered (Mach=3,5,10, and Atwood=0.6,0.8,0.95). The amplitude of initial single mode sinusoidal perturbation of the interface varies from 0\% to 100\% of its wavelength. We analyze the initial growth-rate of the RMI immediately after the shock passage, when the perturbation amplitude increases linearly with time. We find that the initial growth-rate of RMI is a non-monotone function of the amplitude of the initial perturbation. This restrains the amount of energy that can be deposited by the shock at the interface. The maximum value of the initial growth-rate depends strongly and the corresponding value of the initial perturbation amplitude depends only slightly on the shock strength and density ratio. The maximum value of the initial growth-rate increases with the increase of the Atwood number for a fixed Mach number, and decreases with the increase of the Mach number for a fixed Atwood number. We argue that the non-monotonicity of RMI growth-rate is a result of a combination of geometric effect and the effect of secondary shocks. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D4.00007: Numerical modeling of an experimental shock tube for traumatic brain injury studies Michael Phillips, Jonathan D. Regele Unfortunately, Improvised Explosive Devices (IEDs) are encountered commonly by both civilians and military soldiers throughout the world. Over a decade of medical history suggests that traumatic brain injury (TBI) may result from exposure to the blast waves created by these explosions, even if the person does not experience any immediate injury or lose consciousness. Medical researchers study the exposure of mice and rats to blast waves created in specially designed shock tubes to understand the effect on brain tissue. A newly developed table-top shock tube with a short driver section has been developed for mice experiments to reduce the time necessary to administer the blast radiation and increase the amount of statistical information available. In this study, numerical simulations of this shock tube are performed to assess how the blast wave takes its shape. The pressure profiles obtained from the numerical results are compared with the pressure histories from the experimental pressure transducers. The results show differences in behavior from what was expected, but the blast wave may still be an effective means of studying TBI. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D4.00008: Experimental Investigation of the Interaction of Blast Waves Generated by Exploding Wires using Background Oriented Schlieren Jonathan Gross, Veronica Eliasson Work has been performed to experimentally characterize the interaction of a multiple blast waves. The blast waves were generated using an exploding wire system. This system can store up to 400 J of energy in a high voltage capacitor bank. By discharging the capacitors through wires of a diameter of 150 $\mu $m it was possible to produce blast waves with Mach numbers as high as 2.3 at a distance of 40 mm from the center of the blast. A parametric study was performed to measure the behavior of the shocks for a variety of wire thicknesses, voltages, and separation distances. Additionally a background oriented schlieren system was used to quantify the flowfield behind the shocks. The interaction of the shocks featured expected nonlinear phenomena such as the presence of Mach stems, and showed good agreement with results in the shock wave literature. This investigation lays the groundwork for subsequent research that will use exploding wires to experimentally reproduce conditions investigated numerically, in which the effects of multiple converging blast waves on a central target were investigated. [Preview Abstract] |
(Author Not Attending)
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D4.00009: Reflections Over Coupled Surfaces by Means of a High Resolution Setup Meital Geva, Omri Ram, Oren Sadot The reflection patterns over two coupled cylindrical surfaces are studied using a high spatial and high temporal resolution experimental setup. This fully automated setup enabled the repetition of experiments many times while retaining extremely high repeatability. For the investigated moderate shock strengths, the repeatability was less than 0.01 in the Mach number. Each experiment produced a single image with a pixel size of 0.03 mm. All images were later sequentially merged generating a detailed description of a single reflection process. Unlike previous studies in which analysis was subject to human inconsistency, an automatic image processing procedure was used to locate the triple point in each image. The high resolution enabled the experimental detection of the early stages of Mach-reflection as were never demonstrated before. The experimental results were compared with numerical computation and a suitable uncertainty analysis was performed. The reflection over the first model enabled the transitions between MR$\to $RR$\to $MR. These successive transitions have proven the existence of a non-stationary hysteresis shock-wave reflection phenomenon. The reflection over the second model enabled the monitoring of the RR$\to $MR transition and the evolution of a newly three-shock configuration established on the Mach stem of the original reflection (MRMR). It was found that the MRMR$\to $MRRR transition angles could be adjusted to match those obtained over a single cylinder. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D4.00010: ABSTRACT WITHDRAWN |
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