Fast cell determination of the DSMC molecules in multi-stage turbo molecular pump design

In this study, an existing 2D parallel DSMC solver is modified, to analyze the multi-stage turbomolecular pumps more efficiently. Generally, molecule movements are traced cell-by-cell in DSMC solvers both in structured and unstructured meshes in order to determine which cell the DSMC molecule is positioned in. These calculations require time consuming trigonometric operations. If a nonrectangular physical domain can be converted into a rectangular computational domain using curvilinear coordinates, then it would be possible to calculate the DSMC molecule cell information not only in a very short time, but also with simple arithmetic operations. In this study, it is shown that the curvilinear coordinate technique is quite faster compared to cell-by-cell tracing technique. After that, the present 2D parallel DSMC solver is renewed to use implicit molecule indexing to shorten the calculation time even further. Thirdly, dynamically changing representative molecular ratios are used to decrease the statistical errors. Following that, molecule transfer method between computational domains is revised to employ different time steps and blade spacings. Finally, calculations are shown to be in close agreement with the previously published experimental results.