Stability of Supersonic Flow with Injection
Gas injection into supersonic flow past a 5° half-angle cone is studied with three injected gases: helium, nitrogen, and RC318. Experiments are performed in a Mach 4 Ludwieg tube with nitrogen as the free stream gas. The injector section is shaped to admit a "tuned" injection rate where the displacement created by injection counteracts the effects created by the injector geometry. A high-speed schlieren imaging system with a framing rate of 290 kHz is used to study the instability in the region of flow downstream of injection, referred to as the injection layer. Measurements of wavelength, convective speed, and frequency of the instability waves were made. The stability characteristics of the injection layer are found to be very similar to those of a shear layer. The findings of this work suggest that shear layer modes should be a primary concern for future stability analyses of supersonic flow with injection.
© 2019 by Bryan E. Schmidt and Joseph E. Shepherd. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Presented as paper 2016-0599 at the 54th AIAA Aerospace Sciences Meeting, San Diego, CA, 04–08 January 2016; received 5 November 2018; revision received 15 June 2019; accepted for publication 4 July 2019; published online 5 August 2019. The authors acknowledge funding from The Coco and Foster Stanback STEM Fellowship and the Air Force Office of Scientific Research under Grant No. FA9550-10-1-0491. The authors wish to thank Bahram Valiferdowsi for assistance in the laboratory, and Joe Haggerty and Ali Kiani, as well as Mr. Valiferdowsi, for assistance constructing the test articles. The authors thank Jason Schlup and Rich Kennedy for contributions to the development of the fast-acting valve for the Ludwieg tube. Finally the authors thank Prof. Hans Hornung for helpful insights and guidance.
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