Unsteady Behaviors of a Hypersonic Inlet Caused by Throttling in Shock Tunnel

A two-dimensional hypersonic inlet/isolator model that exhibits self-starting characteristics is tested with different exit throttling ratios at a freestream Mach number of 5.9 in a shock tunnel. Various flow characteristics are observed and measured by applying simultaneous high-speed Schlieren imaging and surface pressure measurements. The results indicate that the backpressure generated by the throttling device can be tolerated, and the inlet can maintain the starting mode at low throttling ratios, whereas unstart flows are initiated from the near-choke throttling ratios, and a shock wave oscillation appears. The Schlieren movie demonstrates that the upstream-propagating shocks in the duct play important roles during the oscillation cycles and that the formations of the upstream-propagating shocks are related to the downstream-propagating compression waves/shock waves that encounter the throttling section. The frequency of the shock wave oscillation increases with increasing exit throttling ratios, primarily because of the acceleration of the upstream propagation.