Searching for a near neighbor particle in DSMC cells using pseudo-subcells

Autor: Michael N. Macrossan
Rok vydání: 2010
Předmět:
Zdroj: Journal of Computational Physics. 229:5857-5861
ISSN: 0021-9991
DOI: 10.1016/j.jcp.2010.04.042
Popis: LeBeau et al. (2003) [4] introduced the 'virtual-subcell' (VSC) method of finding a collision partner for a given DSMC particle in a cell; all potential collision partners in the cell are examined to find the nearest neighbor, which becomes the collision partner. Here I propose a modification of the VSC method, the 'pseudo-subcell' (PSC) method, whereby the search for a collision partner stops whenever a 'near-enough' particle is found, i.e. whenever another particle is found within the 'pseudo-subcell' of radius @d centered on the first particle. The radius of the pseudo-subcell is given by @d=Fd"n, where d"n is the expected distance to the nearest neighbor and F is a constant which can be adjusted to give a desired trade-off between CPU time and accuracy as measured by a small mean collision separation (MCS). For 3D orthogonal cells, of various aspect ratios, d"n/L~0.746/N^0^.^3^8^3 where N is the number of particles in the cell and L is the cube root of the cell volume. There is a good chance that a particle will be found in the pseudo-subcell and there is a good chance that such a particle is in fact the nearest neighbor. If no particle is found within the pseudo-subcell the closest particle becomes the collision partner. To limit the CPU time required for large N the search is restricted to a subset of all particles in the cell; the nearest particle from that subset becomes the collision partner. Here the VSC search is restricted to 29 of the remaining particles and the CPU time never increases beyond what is required for N=30. For N>30 the restricted search is as accurate as a standard subcell method using 34 subcells in a 3D cell. The PSC search surveys up to 33 possible collision partners, to yield the same limiting value of MCS, and still save some CPU time. For F=1.1, PSC uses between 12% and 20% less CPU than VSC while the accuracy is within 4% of that for VSC.
Databáze: OpenAIRE
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