ON TRANSITION IN SUPERSONIC AND HYPERSONIC BOUNDARY-LAYERS

The roles of the first and second modes of instability in high-speed b oundary-layer transition are quantified. Linear stability theory and t he N-factor criterion are used to predict transition location. The eff ect of heat transfer is also studied; the results demonstrate that the transition reversal phenomenon can be explained by the opposite effec t of cooling on the first and second modes of instability. A heating s trip can be used to stabilize first-mode waves at supersonic speeds. C ompressibility is destabilizing at free-stream Mach numbers of 2-3.5. The predicted transition location is due to the oblique first modes of instability, up to free-stream Mach numbers between 6 and 6.5. At hig her Mach numbers, the predicted transition location is due to a combin ation of two-dimensional (2-D) first and second modes of instability.