Global Time-Resolved Measurements of Inlet/Isolator Unstart Induced by Mass Injection

The inner surface pressure of an axisymmetric inlet/isolator model was measured using anodized-aluminum pressure-sensitive paint (PSP) viewing through cast acrylic. Temperature-sensitive paint was used to correct for the PSP’s temperature sensitivity. The model was tested under Mach 5.7 flow at Formula: see text under conventional noise conditions. Transverse jet injection with jet-to-inlet mass-flow ratios up to 0.8 was used to induce unstart in the inlet/isolator. Background-oriented schlieren visualization of the inlet shocks was collected simultaneously with the PSP to determine when the inlet unstarted. Computational fluid dynamics results were used to determine off-wall flow structures and quantify approach conditions in the isolator. The dominant frequency of the quasi-steady shock train was 500 to 600 Hz. Coherence analysis revealed a linear relationship between the unsteady pressures downstream of the shock-train leading edge (STLE). A phase difference of Formula: see text was seen between the region immediately downstream of the STLE and the region over approximately 1.5 isolator diameters downstream of the STLE. The PSP and conventional transducer measurements of STLE pressure rise agreed well with each other. The unstart process took approximately 10 to 45 ms, and the peak velocities were Formula: see text, depending on the jet-to-inlet mass-flow ratio. The quasi-steady STLE shock front shape was measured with high spatial resolution and matched that of an upstream inlet shock. The pressure profile shape changed quickly due to the presence of inlet shocks and transient changes due to mass-injection, which has implications to unstart detection methods.