Nonequilibrium and morphological characterizations of Kelvin-Helmholtz instability in compressible flows

TL;DR

This study uses a discrete Boltzmann model to analyze how viscosity and heat conduction influence the development of Kelvin-Helmholtz instability in compressible flows, revealing complex effects on instability growth and nonequilibrium behaviors.

Contribution

It introduces two effective approaches to analyze KHI configurations and kinetic processes, linking morphological and thermodynamic measures to instability evolution.

Findings

Viscosity stabilizes KHI and increases TNE intensities.

Heat conduction initially suppresses then promotes KHI evolution.

Maxima of mixing layer width, TNE intensity, and boundary length occur simultaneously.

Abstract

We investigate the effects of viscosity and heat conduction on the onset and growth of Kelvin-Helmholtz instability (KHI) via an efficient discrete Boltzmann model. Technically, two effective approaches are presented to quantitatively analyze and understand the configurations and kinetic processes. One is to determine the thickness of mixing layers through tracking the distributions and evolutions of the thermodynamic nonequilibrium (TNE) measures; the other is to evaluate the growth rate of KHI from the slopes of morphological functionals. Physically, it is found that the time histories of width of mixing layer, TNE intensity, and boundary length show high correlation and attain their maxima simultaneously. The viscosity effects are twofold, stabilize the KHI, and enhance both the local and global TNE intensities. Contrary to the monotonically inhibiting effects of viscosity, the heat conduction effects firstly refrain then enhance the evolution afterwards. The physical reasons are analyzed and presented.