Turbulent spots in hypervelocity flow
The turbulent spot propagation process in boundary layer flows of air, nitrogen, carbon dioxide, and air/carbon dioxide mixtures in thermochemical nonequilibrium at high enthalpy is investigated. Experiments are performed in a hypervelocity reflected shock tunnel with a 5-degree half-angle axisymmetric cone instrumented with flush-mounted fast-response coaxial thermocouples. Time-resolved and spatially demarcated heat transfer traces are used to track the propagation of turbulent bursts within the mean flow, and convection rates at approximately 91, 74, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, peak, and trailing edge of the spots. A simple model constructed with these spot propagation parameters is used to infer spot generation rates from observed transition onset to completion distance. Spot generation rates in air and nitrogen are estimated to be approximately twice the spot generation rates in air/carbon dioxide mixtures.
© 2017 Springer-Verlag Berlin Heidelberg. Received: 7 January 2017. Revised: 7 February 2017. Accepted: 14 February 2017. Published online: 20 March 2017. This work is based in part on the Ph.D. dissertation of the first author Jewell (2014) and was part of the "Transition Delay in Hypervelocity Boundary Layers by Means of CO22/Acoustic Interactions" project, sponsored by the U.S. Air Force Office of Scientific Research (FA9550-10-1-0491). J. S. Jewell received additional support from the Rhodes Scholarship, the National Defense Science and Engineering Graduate Fellowship, the Jack Kent Cooke Foundation, and the National Research Council Research Associateship. The authors would like to thank Bahram Valiferdowsi (California Institute of Technology) and Nick Parziale (Stevens Institute of Technology) for assistance running T5, and Ross Wagnild (Sandia National Laboratories) for help with the program to compute run conditions. Hans Hornung (California Institute of Technology) suggested animating the heat-transfer contours and Thomas Juliano (Notre Dame) provided advice on exporting movies.