Transactions of Nanjing University of Aeronautics & Astronautics
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An Empirical Method for Prediction of Hypersonic Rarefied Flow Field
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Abstract:
In this paper, 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 costs, most problems in rarefied flow regime are investigated through numerical methods, in which the Direct Simulation Monte Carlo method (DSMC) is widely used. And the unstructured DSMC method is employed here. Flows around a 2D vertical plate at a given velocity 7500m/s are simulated. For gas rarefaction is judged by the free-stream Knudsen number Kn, two vital 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 affected by Kn is anaylyzed. 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 analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of the square of Kn. At last, an empirical method is established, which can be used for the prediction of the hypersonic flow field structure at a given inflow velocity, especially the shock wave position.
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