Stability of highly cooled hypervelocity boundary layers
The influence of high levels of wall cooling on the stability of hypervelocity boundary layers is investigated. Such conditions are relevant to experiments in high-enthalpy impulse facilities, where the wall temperature is much smaller than the free-stream temperature, as well as to some real flight scenarios. Some effects of wall cooling are well known, for instance, the stabilization of the first mode and destabilization of the second mode. In this paper, several new instability phenomena are investigated that arise only for high Mach numbers and high levels of wall cooling. In particular, certain unstable modes can travel supersonically with respect to the free stream, which changes the nature of the dispersion curve and leads to instability over a much wider band of frequencies. The cause of this phenomenon, the range of parameters for which it occurs and its implications for boundary layer stability are examined. Additionally, growth rates are systematically reported for a wide range of conditions relevant to high-enthalpy impulse facilities, and the stability trends in terms of Mach number and wall temperature are mapped out. Thermal non-equilibrium is included in the analysis and its influence on the stability characteristics of flows in impulse facilities is assessed.
© 2015 Cambridge University Press. Received 3 February 2015; revised 20 April 2015; accepted 21 June 2015; first published online 5 August 2015. The authors are grateful to A. Fedorov and A. Tumin for key insights regarding the interpretation of the supersonic modes and helpful discussions of other aspects of the paper. The authors are also grateful to H. Johnson and G. Candler for generously providing use of their STABL stability software package, which was essential for validation at high-enthalpy conditions.
Published - S0022112015003584a.pdf