Gridless DSMC

This work concerns the development of a gridless method for modeling the interparticle collisions of a gas. Conventional fixed-grid algorithms are susceptible to grid-mismatch to the physical system, resulting in erroneous solutions. On the contrary, a gridless algorithm can be used to simulate various physical systems without the need to perform grid-mesh optimization. An octree algorithm provides the gridless character to a direct simulation Monte Carlo (DSMC) code by automatically sorting nearest-neighbor gas particles into local clusters. Automatic clustering allows abstraction of the DSMC algorithm from the physical system of the problem in question. This abstraction provides flexibility for domains with complex geometries as well as a decreased code development time for a given physical problem. To evaluate the practicality of this code, the time required to perform the gridless overhead from the octree sort is investigated. This investigation shows that the gridless method can indeed be practical and compete with other DSMC codes. To validate gridless DSMC, results of several benchmark simulations are compared to results from a fixed-grid code. The benchmark simulations include several Couette flows of differing Knudsen number, low-velocity flow past a thin plate, and two hypersonic flows past embedded objects at a Mach number of 10. The results of this comparison to traditional DSMC are favorable. This work is intended to become part of a larger gridless simulation tool for collisional plasmas. Corresponding work includes a gridless field solver using an octree for the evaluation of long range electrostatic forces. We plan to merge the two methods creating a gridless framework for simulating collisional-plasmas.