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Separation length in high-enthalpy shock/boundary-layer interaction

Davis, Jean-Paul and Sturtevant, Bradford (2000) Separation length in high-enthalpy shock/boundary-layer interaction. Physics of Fluids, 12 (10). pp. 2661-2687. ISSN 1070-6631. doi:10.1063/1.1289553.

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Experiments were performed in the T5 Hypervelocity Shock Tunnel to investigate nonequilibrium real-gas effects on separation length using a double-wedge geometry and nitrogen test gas. Local external flow conditions were estimated by computing the inviscid nonequilibrium flow field. A new scaling parameter was developed to approximately account for wall temperature effects on separation length for a laminar nonreacting boundary layer and arbitrary viscosity law. A classification was introduced to divide mechanisms for real-gas effects into those acting internal and external to viscous regions of the flow. Internal mechanisms were further subdivided into those arising upstream and downstream of separation. Analysis based on the ideal dissociating gas model and a scaling law for separation length of a nonreacting boundary layer showed that external mechanisms due to dissociation may decrease separation length at low incidence but depend on the free-stream dissociation at high incidence. A limited numerical study of reacting boundary layers showed that internal mechanisms due to recombination occurring in the boundary layer upstream of separation cause a slight decrease in separation length relative to a nonreacting boundary layer with the same external conditions. Correlations were obtained of experimentally measured separation length using local external flow parameters computed for reacting flow, which scales out external mechanisms but not internal mechanisms. These showed the importance of the new scaling parameter in high-enthalpy flows, a linear relationship between separation length and reattachment pressure ratio, and a Reynolds-number effect for transitional interactions. A significant increase in scaled separation length was observed in the experimental data at high enthalpy. The increase was attributed to an internal mechanism arising from recombination in the free-shear layer downstream of separation, perhaps altering its velocity profile. This real-gas effect depends on the combined presence of free-stream dissociation and a cold wall.

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Additional Information:©2000 American Institute of Physics. Received 23 November 1999; accepted 29 June 2000. The authors wish to acknowledge Professor Hans Hornung, Professor Anatol Roshko, Professor Joseph Shepherd, and the late Professor Toshi Kubota for their insights, as well as the staff and students of the T5 Hypervelocity Shock Tunnel Laboratory for help setting up and running experiments. Special thanks are due Joseph Olejniczak for providing the computational code along with much invaluable advice on using and modifying it. Cray supercomputer resources were provided through funding by NASA Offices of Mission to Planet Earth, Aeronautics, and Space Science. Experiments were funded by the Air Force Office of Scientific Research under Grant No. F49629-93-1-0338. Additional funding was provided by Caltech.
Subject Keywords:nonequilibrium flow; flow separation; shock waves; boundary layers; laminar flow; external flows; hypersonic flow
Issue or Number:10
Record Number:CaltechAUTHORS:DAVpof00
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3630
Deposited By: Tony Diaz
Deposited On:22 Jun 2006
Last Modified:08 Nov 2021 20:11

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