Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E03: Shock Interactions and Focusing |
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Chair: Lian Duan, Missouri University of Science and Technology Room: Georgia World Congress Center B204 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E03.00001: Visualization of shock wave–grid turbulence interaction in the counter–driver shock tube Akihiro Sasoh, Takahiro Tamba, Gaku Fukushima We have developed a “counter-driver shock tube (CD-ST) in which we can generate two sets of a planar shock wave and a post-shock flow in the opposite directions. The initiations of a planar shock wave and a counter flow are done with sending electrical signals to the diaphragm opening devices on both ends with an appropriate time difference. The experiments were conducted using a newly-developed CD-ST with a total length of 10.1 m. Using side-view shadowgraph, we have successfully visualized shock wave deformation made by the grid turbulence. With a shock Mach number of 1.04 and a turbulent Mach number of 0.024, the side-viewed shock front became much dispersed with a sufficiently long interaction length than 0.3 m; the shock wave front became “wrinkled” and then “broken,” thereby claiming that we have successfully visualized the formation of “broken” shock wave as was suggested by the numerical simulation in Larsson et al. J. Fluid Mech. 717, 293 (2013). |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E03.00002: Shockwave / foam film interaction Quentin Raimbaud, Martin Monloubou, Steven Kerampran, Isabelle Cantat Foams are very efficient to absorb shock waves, and are used in demining situations. The wave/film interaction involves complex processes (Bremond & Villermaux, J. Fluid. Mech. 2005) not fully understood yet. To elucidate the various processes leading to film rupture under shock, we produce foam films in a transparent shock tube and image them at 200000 fps, by direct visualization or ombroscopy. Deformations at a millimetric scale are observed before the film eventually ruptures, in which the film thickness heterogeneities play a crucial role : pieces of film of different thicknesses are accelerated at various rates, leading to film tear out, and only the most homogeneous films have time to destabilize via the Rayleigh Taylor instability described in the literature. The orientation of the film with respect of the incoming wave also influences the film deformation and, using dedicated film structure, we show that the tangential component of the acceleration generates wrinkling of well defined wave length. The pressure signals induced by the shock / film interaction are in good agreement with numerical simulations and show the short delay generated by the film, contributing to the wave attenuation. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E03.00003: Shock Wave Dynamics Explored: A Parametric Analysis of the 2-D Case William M Mellor, Veronica Eliasson Unique to this research is a novel exploding wire system that can create shock waves that are consistent with those exhibiting blast type flow phenomena. In this talk, the relationship of shock waves -- with a decaying pressure zone behind the shock front -- is investigated in 2D experimentally. Results are obtained using a novel exploding wire system coupled with a Shimadzu HPV-X2 high-speed camera, and a schlieren setup. The exploding wire setup was designed to pass a controlled amount of current (10kV--40kV) through a thin wire (0.05mm) to create a shock wave with tunable properties. This research focuses primarily upon the investigation of the regular to irregular transition regime. Qualitative analysis depicts shock wave evolution and Mach stem formation. Results were later post-processed utilizing an in-house code to further determine quantitative phenomena, including the temporal evolution of radius vs time and Mach number vs time. Additionally, simultaneously converging shock-shock interactions are also investigated, and resulting relationships analyzed. Results obtained aim to better elucidate the characteristic changes of shock wave dynamics when the flow is impeded either through physical boundaries, or via other shock waves. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E03.00004: Analysis of irregular Mach reflections of explosively-driven shock waves from surfaces Kyle O Winter, Michael John Hargather, Chi Mai When shock waves reflect from surfaces at angles of attack, the reflection generated can be classified as either a regular oblique or an irregular Mach reflection. Mach reflections contain a normal shock, the Mach stem, that forms to allow conservation of mass, and results in a significant increase in pressure compared to an oblique shock wave reflection. Shock polar analysis is used to identify the regions of Mach number and angle combinations that will result in the formation of irregular shock reflections. The structure of several irregular reflections is analyzed to estimate the peak overpressure and other characteristics for each type of reflection. A developed analytical model of shock reflections is then used to determine the reflection type and characteristics from varying height of burst from a scaled explosive weight. This approach can be used to analytically determine and optimize the overpressure generated by explosively driven shock waves produced at varying heights of burst. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E03.00005: Vortex formation in shock interaction with a deformable ellipsoidal particle Kei Fujisawa, Prashanth Sridharan, Thomas L Jackson, Ju Zhang, S Balachandar We present our numerical study of shock interaction with a deformable ellipsoidal particle. Numerical simulations were carried out using fully resolved multi–material Euler equations for shock interaction with a deformable aluminum particle in nitromethane. We compute the circulation and the unsteady drag coefficient as a function of time. As the shock propagates over the particle we observed the vorticity production owing to the baroclinic effect and it is primarily initiated near the interface of the particle. After the passage of a shock over a particle, the generated vortex traverses downstream, thus generating low pressure in the downstream side of the particle. This mechanism leads to the generation of a quasi–steady drag force even after the passage of the shock. The peak circulation is computed as a function of shock Mach number and the initial ellipticity of the particle, and we show that the absolute value of the peak circulation increases with increasing shock Mach number and ellipticity of the particle. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E03.00006: The Interaction of a Homogeneous Field of Acoustic Waves with a Shock Wave Chao Zhang, Yuchen Liu, Lian Duan, Sarma L Rani Direct numerical simulations (DNS) and linear interaction analysis (LIA) are used to examine the significant flow characteristics associated with a homogeneous field of acoustic waves passing through a nominally normal shock wave. The full-fledged nonlinear simulations and the linear analysis are enabled by a pre-cursor numerical database of boundary-layer acoustic radiation that provides incident acoustic fields with high degree of physical realism and applicability. The research contributes to the fundamental understanding of the interaction of a shock wave with a field of turbulence by characterizing its behaviors in the pure dilatational limit and complements existing studies of shock/turbulence interaction with a vorticity-dominated incident turbulent field. |
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