Discrete Boltzmann study on Kelvin-Helmholtz instability: nonequilibrium and morphological characterizations

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. Both hydrodynamic and thermodynamic nonequilibrium (TNE) manifestations, as well as morphological characterizations are extracted to analyze and understand the configurations and kinetic processes. Technically, we present two effective approaches. One is to determine the thickness of mixing layers through tracking the distribution and evolution of the TNE measures. The other is to evaluate the growth rate of KHI from slopes of Minkowski measures. Physically, it is found that the time evolutions of width of mixing layer, TNE intensity, and boundary length show high correlation and attain their maxima simultaneously. The viscosity effects are twofold. One is to stabilize the KHI. The other is to enhance both the local and global TNEs. Contrary to the monotonically inhibiting effects of viscosity, the heat conduction effects first refrain then enhance the evolution afterwards. The physical reasons are analyzed.