A gradient-compression-based compact high-order gas-kinetic scheme on three-dimensional hybrid unstructured mesh

In this paper, the compact gas-kinetic scheme for compressible flow is extended to hybrid unstructured mesh. Based on both cell-averaged flow variables and their gradients updated from time accurate gas evolution model at cell interfaces, a compact third-order least-square-constrained reconstruction can be obtained on unstructured mesh and a multi-resolution WENO reconstruction is adopted in case of discontinuous solutions. Moreover, a compression factor for the cell-averaged gradients is proposed to take into account the possible discontinuity in flow variables at cell interface, which significantly improves the robustness of the compact scheme for high-speed flow computation on irregular mesh and preserves the accuracy. Numerical tests from incompressible to hypersonic flow are presented to demonstrate the broad applicability of the gradient-compression-based high-order compact scheme.