Long Time Observation of the Richtmyer-Meshkov Instability

Introduction

Richtmyer-Meshkov (RM) instability occurs when a interface separating two fluids of different density is impulsively accelerated in the direction of its normal. It is one of the most fundamental fluid instabilities and is of importance to the fields of astrophysics and inertial confinement fusion. RM instability experiments are normally carried out in shock tubes, where the generation of a sharp, well-controlled interface between gases is difficult, so there is a dispersion in terms of experimental results. The experiments presented here were conducted in a horizontal shock tube where the materialization of the initial interface was achieved by a thin nitrocellulosic membrane (0.5 μm thick) deposited on a stereolithographed grid support, computer-aided designed and constructed with chosen shape and dimensions. As diagnostic, we used laser sheet flow visualization to yield time-motion image sequences of the linear and the non-linear developments of the instability. In previous investigation [1], we have already shown that residual pieces from the membrane constituting the initial interface tend to delay the interpenetration in the light-to-heavy gas configuration and specifically during the linear stage of the interface evolution. In order to reduce these effects in the present experiments, we have increased the strength of the shock wave (Mach~1.5). We have also extended the test section from 0.46 m to 1.5 m which allows the instability to grow further and thus to observe the whole nonlinear phase until the transition to turbulence. The present paper summarizes the results obtained during this study undertaken for air/SF₆ and air/He gas combinations (positive and negative Atwood numbers, respectively) in 2D and 3D geometries.