An entropy preserving implicit unified gas-kinetic wave-particle method for radiative transport equation

In this paper, one remarkable progress has been made to the unified gas-kinetic wave-particle method that removes the time step constraint. As long as the time resolution is acceptable, the Courant number can be set as unlimited large number. The non-equilibrium transport flow physics will be accurately captured without introducing artificial closure to the distribution function. The main idea is to introduce two time parameters to control the time evolution process, namely the physical time scale parameter and the numerical time step parameter. Based on the physical time scale parameter, the governing equations in discretized form will be derived, whose underline physics will not change with the value of the numerical marching step. We define the preservation of non-equilibrium state as the entropy preserving. Besides physical invariance, the proposed implicit unified gas-kinetic wave-particle method is asymptotic preserving and regime adaptive. Multidimensional 2D and 3D codes are developed for the inertial confinement fusion engineering application. Some multiscale tests are simulated to verify the numerical method as well as the programs.