Injection into Supersonic Boundary Layers

Creators: Schmidt, B. E.; Bitter, N. P.; Hornung, H. G.; Shepherd, J. E.

Abstract

A method for injection of gas into the boundary layer on a slender body in supersonic flow while minimizing perturbation to the mean flow is examined. Injection of gas is equivalent to a sudden increase in the displacement thickness of the boundary layer, which produces an oblique shock that propagates into the inviscid region of the flow. It is found that modification of the geometry of the body can compensate for the increased displacement thickness created by injection and minimize the production of oblique waves. However, the resulting near-wall injection layer is observed to be unstable and a turbulent boundary layer develops downstream of the injection region. The instability of the flow is examined experimentally using high-speed schlieren visualization and numerically using linear stability analysis of velocity profiles from a compressible Navier–Stokes computation. At the present postshock Mach number of about 3.8, both first- and second-mode instabilities are active, though computations predict that the first mode is primarily responsible for transition downstream of the injector.

Additional Information

© 2015 by the American Institute of Aeronautics and Astronautics, Inc. Presented as Paper 2014-2496 at the 7th AIAA Theoretical Fluid Mechanics Conference, Atlanta, GA, 16–20 June 2014; received 30 December 2014; revision received 1 June 2015; accepted for publication 16 August 2015; published online 7 October 2015. This work was sponsored in part by the Air Force Office of Scientific Research (AFOSR) and NASA through the National Center for Hypersonic Research in Laminar-Turbulent Transition and also by AFOSR award number FA9550-10-1-0491. The views expressed herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of AFOSR or the U.S. Government. The authors would like to thank Nicholaus Parziale and Bahram Valiferdowsi for guidance and assistance in the laboratory. The authors would additionally like to acknowledge Joseph Jewell, Ivett Leyva, and Ross Wagnild for previous work done on this topic. Finally, the authors thank Alexander Fedorov for the concept of using a negative slope on the cone surface to compensate for injection. Without this key idea, this work would not have been performed.

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