Measurements of Instability in Supersonic Flow with Injection by Time-Resolved Flow Visualization
Experiments were performed in a Mach 4 Ludwieg tube to examine the transition process in flow over a sharp cone with boundary layer injection. Full-field images with nitrogen, helium and RC-318 injection reveal that transition occurs earlier with higher injection rates and with lighter injected gas. High-speed imaging at 290 kHz allows the measurement of wavelength and convective velocity by auto- and cross-correlation, respectively, in the cases with nitrogen injection. The wavelength is found to be approximately 8 mm with a convective velocity of 515 m/s, resulting in a frequency range of 60-70 kHz. These properties of the instability waves are roughly constant over all injection rates tested even though the thickness of the injection layer varies by a factor of two.