Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session H4: Turbulence and Mixing I |
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Chair: Bertrand Rollin and Thomas Jackson, University of Florida Room: Grand H |
Tuesday, June 16, 2015 9:15AM - 9:30AM |
H4.00001: Direct Numerical Simulation of Turbulence and Mixing in Highly Compressible Flows Yifeng Tian, Farhad Jaberi, Zhaorui Li, Daniel Livescu The effects of normal shock waves on isotropic turbulence and scalar mixing are studied by direct numerical simulation (DNS) of fully compressible equations with high-order monotonicity-preserving and compact finite-difference numerical schemes for various flow and scalar conditions. Detailed examinations of the turbulence and scalar statistics such as the turbulent kinetic energy and scalar variance indicate that the numerical method is accurate and is able to correctly capture the shock-turbulence interactions and scalar mixing near and away from the shock even at very high Mach numbers. As expected, the shock wave increases the small-scale turbulence and the skewness and flatness of the turbulent velocity fluctuations, but the turbulent compressibility is actually decreased by the shock. The effect of shock on the turbulence was to found be strongly dependent on the pre-shock turbulence parameters such as the turbulence intensity. The enhancement of scalar mixing by the shock is also found to be dependent on the pre-shock scalar structure. The mechanisms responsible for the modification of turbulence and scalar mixing are identified by analyzing the flow structure and the transport equations for the Reynolds stress, vorticity and scalar variance inside and outside the shock zone. [Preview Abstract] |
Tuesday, June 16, 2015 9:30AM - 9:45AM |
H4.00002: Modeling and Numerical Challenges in Eulerian-Lagrangian Computations of Shock-driven Multiphase Flows Angela Diggs, Sivaramakrishnan Balachandar The present work addresses the numerical methods required for particle-gas and particle-particle interactions in Eulerian-Lagrangian simulations of multiphase flow. Local volume fraction as seen by each particle is the quantity of foremost importance in modeling and evaluating such interactions. We consider a general multiphase flow with a distribution of particles inside a fluid flow discretized on an Eulerian grid. Particle volume fraction is needed both as a Lagrangian quantity associated with each particle and also as an Eulerian quantity associated with the flow. In Eulerian Projection (EP) methods, the volume fraction is first obtained within each cell as an Eulerian quantity and then interpolated to each particle. In Lagrangian Projection (LP) methods, the particle volume fraction is obtained at each particle and then projected onto the Eulerian grid. Traditionally, EP methods are used in multiphase flow, but sub-grid resolution can be obtained through use of LP methods. By evaluating the total error and its components we compare the performance of EP and LP methods. The standard von Neumann error analysis technique has been adapted for rigorous evaluation of rate of convergence. The methods presented can be extended to obtain accurate field representations of other Lagrangian quantities. Most importantly, we will show that such careful attention to numerical methodologies is needed in order to capture complex shock interaction with a bed of particles. [Preview Abstract] |
Tuesday, June 16, 2015 9:45AM - 10:00AM |
H4.00003: Experimental drag histories of shock accelerated micrometer sized particles Gregory Orlicz, Adam Martinez, Kathy Prestridge The horizontal shock tube facility at Los Alamos is used to investigate the drag forces on micrometer sized particles dispersed in air when they are accelerated by a shock. Eight-frame, high-speed particle tracking velocimetry/accelerometry (PTVA) diagnostics are implemented to measure the trajectory of individual particles with high spatial and temporal resolution, and a shadowgraphy system is used to measure the shock location. We will present experiments covering a range of Mach numbers, particle sizes, and particle densities, to explore the drag forces on both solid particles and liquid droplets. Results are compared to those predicted by the quasi-steady drag correlation and other empirical unsteady drag models. Estimations of the drag coefficients are found to be significantly higher than the models predict for solid spherical particles. Measurements at this facility will be used to further develop and validate models for unsteady drag. [Preview Abstract] |
Tuesday, June 16, 2015 10:00AM - 10:15AM |
H4.00004: Oblique Shock Interaction with a Laminar Cylindrical Jet Patrick Wayne, Dell Olmstead, C. Randall Truman, Peter Vorobieff, Sanjay Kumar We present an experimental study of a planar shock interaction with an initially cylindrical, diffuse density interface, where the angle $\alpha$ between the plane of the shock and the axis of the cylinder can be zero (planar normal interaction) or non-zero (oblique interaction). The interface is formed by injecting a laminar jet of a heavy gas mixture (sulfure hexafluoride, acetone, nitrogen) into quiescent air. The jet is stabilized by an annular co-flow of air to minimize diffusion. Interaction between the pressure gradient (shock front) and density gradients leads to vorticity deposition, and during the subsequent evolution, the flow undergoes mixing (injected material -- air) and eventually transitions to turbulence. Several parameters affect this evolution, including the angle $\alpha$, the Atwood number (density ratio), and the Mach number of the shock. For quantitative and qualitative characterization of the influence of these parameters, we use flow visualization in two planes that relies on planar laser-induced fluorescence (PLIF) in acetone, which forms a part of the injected material. [Preview Abstract] |
Tuesday, June 16, 2015 10:15AM - 10:30AM |
H4.00005: Numerical simulation of multi-material mixing in an inclined interface Richtmyer-Meshkov instability Akshay Subramaniam, Sanjiva Lele The Richtmyer-Meshkov instability arises when a shock wave interacts with an interface separating two fluids. In this work, high fidelity simulations of shock induced multi-material mixing between air and SF6 in a shock tube are performed for a Mach 1.5 shock interacting with a planar material interface that is inclined with respect to the shock propagating direction. In the current configuration, unlike in the classical sinusoidal interface case, the evolution of the interface is fully non-linear from early time onwards. The simulations attempt to replicate an experiment conducted at the Texas A\&M fluid mixing shock tube facility. Simulations of this problem at multiple spatial resolutions (upto 270 million grid points) have shown that even low order statistics like the net circulation are hard to capture at resolutions where the classical RM cases yield good results. Tight coupling between numerics and flow physics and large range of spatial scales make this a challenging problem to simulate numerically. Simulations shown are conducted with an extended version of the MIRANDA solver developed by Cook et. al (2007) which combines high-order compact finite differences with localized non-linear artificial properties for shock and interface capturing. [Preview Abstract] |
Tuesday, June 16, 2015 10:30AM - 10:45AM |
H4.00006: Turbulent mixing induced by Richtmyer-Meshkov instability Jeffrey Jacobs, Vitaliy Krivets, Robert Morgan, Everest Sewell A vertical shock tube is used for experiments on the Richtmyer-Meshkov instability. A membrane-less interface is formed by opposed gas flows in which the light and heavy gases enter the shock tube from the top and from the bottom of the driven section. An air/SF$_{6}$ gas combination is used and an $M =$\textit{1.2} incident shock wave impulsively accelerates the interface. Initial perturbations are generated by harmonically oscillating the gases either horizontally to produce standing internal waves having sinusoidal shape, or vertically, using two loudspeakers mounted in the shock tube wall, to produce Faraday resonance resulting in more random short wavelength perturbations. Planar Mie scattering is used to visualize the flow using a laser sheet to illuminate smoke particles seeded in the air. Image sequences are captured using high-speed video cameras. New experiments are presented in which the full three-dimensional initial perturbation is recorded immediately prior to shock interaction using a galvanometer to sweep the laser sheet across the test section, producing a volumetric image of the initial perturbation. Comparisons are made between experimental measurements and numerical simulations. [Preview Abstract] |
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