Nonequilibrium kinetics effects in Richtmyer-Meshkov instability and reshock process

Abstract

Nonequilibrium kinetic effects are widespread in fluid systems and might have a significant impact on the inertial confinement fusion ignition process, and the entropy production rate is a key factor in accessing the compression process. But relevant research is little due to the lack of convenient physical model. In this work, we study the Richtmyer-Meshkov instability (RMI) and the reshock process by a two-fluid discrete Boltzmann method (DBM). The work starts from interpreting the experiment by Collins and Jacobs [J. Fluid Mech. 464, 113-136 (2002)]. Firstly, the DBM result for the perturbation amplitude evolution is in good agreement with that of experiment. It is found that shock wave causes substances near the substance interface to deviate more significantly from their thermodynamic equilibrium state. Greatly different from the case of normal shocking on unperturbed plane interface between two uniform media, which is well described by the Rankine-Hugoniot relations and where all Thermodynamic Non-Equilibrium (TNE) quantities quickly recover to zero behind the shock front, in the RMI case, the TNE quantities show complex but inspiring kinetic effects in the shocking process and behind the shock front. The kinetic effects are detected by two sets of TNE quantities. The first set are |∆ * 2 |, ∆ * 3,1 , ∆ * 3 , and ∆ * 4,2 . They correspond to the intensities of the Non-Organized Momentum Flux(NOMF), Non-Organized Energy Flux(NOEF), flux of NOMF and flux of NOEF. All the four TNE measures abruptly increase in the shocking process. ∆ * 3,1 and ∆ * 3 have the same dimension and show similar behaviors. They continue to increase in a much lower rate behind the shock front. |∆ * 2 | and ∆ * 4,2 have different dimensions, but show similar behaviors. They quickly decrease to be very small behind the shock front. The second set of TNE quantities are ṠNOMF , ṠNOEF and Ṡsum . They are entropy production rates due to NOMF, NOEF and their summation. It is found that the mixing zone is the primary contribution region to the ṠNOEF , while the flow field region excluding mixing zone is the primary contribution region to the ṠNOMF . Each substance behaves differently in terms of entropy production rate, and the light fluid has a higher entropy production rate than the heavy fluid.