In this thesis, the unified gas-kinetic wave-particle (UGKWP) method for monatomic and diatomic gas flow simulations has been constructed on three-dimensional unstructured mesh with parallel computing capability. The time evolution in the UGKWP method is composed of analytical wave and stochastic particles, where the accumulating effect from particle transport and collision is modeled on the mesh size scale within a time step. With the dynamic wave-particle decomposition, the UGKWP method is able to capture the continuum wave interaction and rarefied particle transport without resolving down to the kinetic scale. Moreover, in UGKWP modeling, translational and rotational non-equilibrium has been taken into consideration.

In addition, UGKWP achieves high efficiency in different flow regim...[ Read more ]

In this thesis, the unified gas-kinetic wave-particle (UGKWP) method for monatomic and diatomic gas flow simulations has been constructed on three-dimensional unstructured mesh with parallel computing capability. The time evolution in the UGKWP method is composed of analytical wave and stochastic particles, where the accumulating effect from particle transport and collision is modeled on the mesh size scale within a time step. With the dynamic wave-particle decomposition, the UGKWP method is able to capture the continuum wave interaction and rarefied particle transport without resolving down to the kinetic scale. Moreover, in UGKWP modeling, translational and rotational non-equilibrium has been taken into consideration.

In addition, UGKWP achieves high efficiency in different flow regimes. As the local cell's Knudsen number varies, the UGKWP becomes a particle method in the highly rarefied flow regime. In the continuum ow regime, the UGKWP will automatically get back to the gas-kinetic scheme (GKS), a macroscopic variables based Navier-Stokes flow solver without particles, because of the dominant wave contribution. When compared to the discrete velocity method (DVM)-based unified gas-kinetic scheme (UGKS) for high-speed, high-temperature flow simulation, the computational cost and memory requirements in UGKWP could be lowered by several orders of magnitude.

In the highly rarefied regime, particle transport and collision will play a dominant role. Due to the single relaxation time modeling in particle collision, there is a noticeable discrepancy between the UGKWP solution and the full Boltzmann or DSMC result, notably in the high Mach and Knudsen number cases. To go beyond the kinetic relaxation model, a heuristic modeling on particle collision time according to the particle velocity will be implemented in UGKWP. As a result, the novel modeling dramatically improves the performance of UGKWP in capturing non-equilibrium effects for both monatomic and diatomic gas flows. There is a perfect match between UGKWP and reference solutions in the highly rarefied regime, whereas its accuracy in the continuum regime is still retained.

In summary, the UGKWP method has been validated with the reference results and experimental measurements in various cases, from one-dimensional shock structure to three-dimensional flows at different Mach and Knudsen numbers. Thanks to wave-particle formulation, even with a personal workstation, the UGKWP method has great potential in simulating three-dimensional multiscale transport with the coexistence of continuum and rarefied flow regimes, particularly for high-speed non-equilibrium flow surrounding a spacecraft in near-space flight.