Transactions of Nanjing University of Aeronautics & Astronautics
An Empirical Method for Prediction of Hypersonic Rarefied Flow-Field Structure
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Abstract:
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 7 500 m/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 Knvaries 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 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 analyzing, it is proved that hypersonic rarefied flow field expands outward linearly with the increase of √Kn. 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.
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CHINA AERO-SCIENCES
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