Robust cut-cell algorithms for DSMC implementations employing multi-level Cartesian grids

Robust cut-cell algorithms are detailed for general multi-level Cartesian grid direct simulation Monte Carlo (DSMC) implementations. Different approaches for each component of the cut-cell algorithms are elaborated and compared, based on time efficiency, robustness, and ease of implementation. Special situations that arise in sorting the surface triangles, calculating the cut-cell volume, and identifying multiple cut-volumes contained in a single Cartesian cell, are handled by the algorithms, and their effects on the overall simulation results are analyzed using test cases. Three-dimensional DSMC simulations are conducted for a Mach number 20.2 N ₂ gas flowing over a Planetary Probe geometry showing good agreement with experimental heat flux measurements. Rarefied flow over a geometry resembling the MIR Space Station is also conducted, to demonstrate the ability of the proposed cut-cell algorithms to handle complex geometries. The time required to cut the surface meshes from the background Cartesian grids and to calculate the volume of the resulting cut-cells is found to be comparable to the time cost for one DSMC simulation time step for cases considered.