Beyond Richtmyer-Meshkov Instability

Richtmyer-Meshkov instability (RMI) develops on an impulsively accelerated, initially perturbed density interface in fluid. The stability problem for such an interface can be initially considered using the same simplifications as Kelvin-Helmholtz and Rayleigh-Taylor instabilities: ideal fluid, two dimensions, small perturbations. This work was carried out by R.D. Richtmyer in the late 1950s, and the first experimental observations of RMI were published by E.E. Meshkov in the 1960s. Since then, major progress was made in understanding RMI, which is relevant to a large number of problems, from astronomy to engineering. The focus of this talk is on many of these problems where the classical formulation fails to describe either the complexity of the situation or the dominant instability mechanism. An important case of the former is shock interaction with a multiphase medium, where a macroscopic density interface may not exist, but volume-averaged density is non-uniform. Such an interaction can lead to vortex formation due to shock-driven multiphase instability (SDMI). An example of the latter (dominant instability) is shock interaction with a planar density interface at an angle to the plane of the shock. Vorticity deposition mechanism in this case is the same as for RMI, but it results in formation of a vortex sheet developing into shock-driven Kelvin-Helmholtz instability. We discuss the possibility of formulating a generalized framework for these problems, including introduction of dimensionless parameters and scale selection mechanisms.