Development of an amr octree DSMC approach for shock dominated flows

The present work is a continued effort of the development of the SUGAR code for simulating a hypersonic flow over a double wedge at a Knudsen number of 0.000284. The current work describes verification of the code for Borgnakke-Larsen continuous rotational relaxation model and computation of surface coefficients for hypersonic flows over a hemisphere and a double wedge at Knudsen numbers of 0.277 and 0.020, respectively. Further, the paper mainly describes attempts to solve two main performance bottlenecks in making the code simulate at continuum-like conditions, first, the scalability of the code for more than 128 processors by reducing the communication and evenly balancing the computational load, and second, improve the algorithmic performance of the code by eliminating the expensive recursive tree traversal inherent in Octree based mesh structure. In order to resolve the first issue sophisticated graph-partitioners have been use, however, with no success. However, significant performance improvement has been obtained by linearizing the Octree using Morton-Z space filling curve. Based on these findings, a prediction is made of time required to run the main experimental case.