Prediction of Chemical Nonequilibrium Flow Structure at Different Free-Stream Knudsen Numbers
Publication: Journal of Aerospace Engineering
Volume 29, Issue 5
Abstract
A numerical study is conducted to investigate the effects of the inflow Knudsen number () on hypersonic chemical nonequilibrium rarefied flows using the unstructured direct simulation Monte-Carlo (DSMC) method, and an empirical formula for fast prediction of flow-field structure for different values of is proposed and verified. First, the flow around a vertical plate is analyzed at a free-stream velocity of using a perfect-gas model with inflow values ranging from 0.035 to 13.36. Through analysis of the flow-field characteristics with varying values, a linear expansion law of flow-field versus the square root of is discovered and an empirical formula based on least-squares fitting is developed for fast prediction of the flow structure at different values of . Further, the effects of chemical nonequilibrium on hypersonic rarefied flow-field structure are investigated to verify the applicability of the empirical formula. Finally, cases of the cylinder flow are simulated in the regimes from continuum flow to free-molecular flow using a five-species chemical reaction model. The flow-field characteristics with varying values, with the chemical nonequilibrium model, agrees well with those for perfect-gas conditions. It is shown that the empirical formula is also suitable for the use of flow with chemical reactions. The shock position in a continuum-flow case predicted by the empirical method agrees well with data from the literature. The applicability and accuracy of this method over a wide range of have been verified.
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Acknowledgments
The authors would like to extend their appreciation to Professor Wang, and Professor Xia at Nanjing University of Aeronautics and Astronautics (NUAA) for their instructions on the DSMC method and lots of discussions about the study. The authors would also like to thank Yan Xiaoxue from NUAA who provided great help in document revision.
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Published In
Journal of Aerospace Engineering
Volume 29 • Issue 5 • September 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Jul 26, 2015
Accepted: Feb 19, 2016
Published online: May 6, 2016
Published in print: Sep 1, 2016
Discussion open until: Oct 6, 2016
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