An Empirical Method for Prediction of Hypersonic Rarefied Flow-Field Structure

摘要

Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field .Due to the extremely difficult experiment ,limited wind-tunnel conditions and high cost ,most problems in rarefied flow regime are investigated through numerical methods ,in which the direct simulation Monte-Carlo (DSMC) method is widely adopted .And the unstructured DSMC method is employed here .Flows around a vertical plate at a given velocity 7500 m/s are simulated .For gas rarefaction is judged by the free-stream Knudsen number (K n) ,two vi-tal factors are considered :molecular number density and the plate′s length .Cases in which Kn varies from 0 .035 to 13 .36 are simulated .Flow characters in the whole rarefied regime are described ,and flow-field structure affect-ed by Kn is analyzed .Then ,the dimensionless position D﹡ of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation .Through flow-field tracing and least-square numerical method an-alyzing ,it is proved that hypersonic rarefied flow field expands outward linearly with the increase of K n .An empirical method is proposed ,which can be used for the prediction of the hypersonic flow-field structure at a given inflow velocity ,especially the shock wave position .