Article

Gridless DSMC

FOCUS Center, Physics Department, University of Michigan, 450 Church Street, Ann Arbor, MI 48109-1120, United States; Mathematics Department, Michigan State University, D304 Wells Hall, East Lansing, MI 48824-1027, United States
Journal of Computational Physics DOI:10.1016/j.jcp.2008.04.038 pp.8035-8064

ABSTRACT This work concerns the development of a gridless method for modeling the inter-particle 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.

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Keywords

complex geometries
 
Conventional fixed-grid algorithms
 
decreased code development time
 
DSMC algorithm
 
fixed-grid code
 
grid-mesh optimization
 
gridless algorithm
 
gridless field solver
 
gridless framework
 
gridless method
 
gridless overhead
 
inter-particle collisions
 
larger gridless simulation tool
 
low-velocity flow
 
octree algorithm
 
range electrostatic forces
 
simulating collisional-plasmas
 
traditional DSMC
 
two methods
 
validate gridless DSMC