Efficient simulation of multidimensional continuum and non-continuum flows by a parallelised unified gas kinetic scheme solver

We develop an efficient, parallel, gas-kinetic solver for computing both continuum and non-continuum flows over non-Cartesian geometries by utilising the unified gas kinetic scheme (UGKS). UGKS, however, requires the computationally expensive update of a six-dimensional phase space at each time step restricting its application to canonical, laminar problems and simple geometries. In this paper, we demonstrate that the applications of UGKS can be increased by parallelising it and combining it with a recently developed, Cartesian grid method (UGKS-CGM). We demonstrate that our Cartesian grid methodology as well as UGKS parallelization perform and scale well on a range of numerical test cases even for a very large number of cores. Finally, we demonstrate that the solver accurately computes canonical turbulence at low Knudsen numbers. These results demonstrate that the parallelised UGKS code can be utilised to effectively study the non-equilibrium effects of rarefaction on laminar and turbulent non-continuum flows.