Eigen helicity density: A new vortex identification scheme and its application in accelerated inhomogeneous flows

Turbulence initiated by Richtmyer-Meshkov (RM) instability provides an important environment for studying three-dimensional, high-speed, compressible, and variable-density flow physics. The active baroclinic term in the vorticity evolution equation complicates the vortex dynamics and challenges existing vortex identification schemes. In this paper, we examine the insufficiency of existing vortex identification schemes when applied to a simulated RM flow [Zhang et al., J. Turbul. 6, 1 (2005)]. We propose a new scheme, eigen helicity density (He), based on the eigen analysis of the velocity gradient tensor. This Galilean invariant scheme successfully identifies vortex tubes in the same simulation.