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CNA Seminar/Colloquium/Joint Pitt-CNA Colloquium
Snejana Abarji
Carnegie Melllon University
Title: Scale coupling in Richtmyer-Meshkov flows

Abstract: We systematically study the Richtmyer-Meshkov instability (RMI) induced by strong shocks for fluids with contrasting densities and with small and large amplitude initial perturbations imposed at the fluid interface. The Smoothed particle hydrodynamics code (SPHC) is employed to ensure accurate shock capturing, interface tracking, and accounting for the dissipation processes. Simulations results achieve good agreement with existing experiments and with the rigorous theoretical analyses including zero-order theory describing the post-shock background motion of the fluids, linear theory providing RMI growth-rate in a broad range of the Mach and Atwood numbers, weakly nonlinear theory accounting for the effect of the initial perturbation amplitude on RMI growth-rate, and highly nonlinear theory describing evolution of RM bubble front.

We report the following findings: (1) The amount of energy that can be deposited by the shock at the RM-unstable interface is restrained. A significant part of the shock energy goes into compression and background motion of the fluids. (2) The initial amplitude is key factor of RMI evolution. The initial growth-rate of RMI is a non-monotone function of the initial amplitude. (3) At late times RM flow remains laminar rather than turbulent, and RM bubbles flatten and decelerate. In the fluid bulk, the dynamics at small-scale is heterogeneous, and is characterized by reverse cumulative jets, non-uniform velocity fields, local micro-structures, high pressure regions, and `hot spots'. We show that the complicated character of scale coupling of RMI suggests new possibilities for flow mitigation and control.

Recording: http://mm.math.cmu.edu/recordings/cna/snejana_abarji_small.mp4
Date: Thursday, September 17, 2015
Time: 1:30 pm
Location: Wean Hall 7218
Submitted by:  David Kinderlehrer