Transition between unsteady flow states over a high-speed spike-cylinder body

The spike-cylinder, which consists of a spike as the fore-body and a right-circular cylinder as the aft-body, is a canonical geometry used in high-speed flow studies. This flow exhibits two distinct states of unsteadiness, termed "pulsation" and "oscillation." Pulsations are characterized by large-amplitude shock wave motion, whereas oscillations are characterized by small-amplitude unsteady distortions in shock wave structure. The flow state is determined by the single governing geometric parameter -- ratio of the spike length L to the cylinder diameter D. The present effort is aimed at obtaining a detailed understanding of the mechanics of transition between flow states. Wind tunnel experiments at Mach 6 were performed with spike-cylinder models of various L/D values in the range 0.2 to 4. Particular attention was given to L/D values around 1.5, since transition between flow states nominally occurs at L/D = 1.5. High-speed schlieren recorded in these experiments allows for careful visualization of changes in the flow structure during the transition process. The full set of experimental results and a discussion will be presented at the meeting.