Preliminary experiment and analysis of supersonic inlet buzz

Abstract

The inlet buzz phenomenon was investigated experimentally and analytically. An external-compression axisymmetric inlet model, having 74 mm in cowl lip diameter, was tested in the 229x229 sq mm blowdown wind tunnel at Mach 2.4. The test facility has shown potential for the supersonic inlet research. The occurrence of inlet buzz was indicated by the continuous shock oscillation and the static pressure fluctuation. The hypothesis based on internal pressure measurement and shadowgraph pictures during stable operations revealed the substantial influence of the separated flow inside the model. Possible increase in subsonic Mach number at the inlet entrance with decreasing exit throttle area, which could promote an instability, was suggested. A basic theoretical shock-plenum system was developed to simulate the inlet buzz behavior and identify its controlling mechanisms. This nonlinear model was governed by the non-stationary shock wave relation, the plenum chamber mass balance, and the entrance blocking effect, as introduced by the vortex sheet theory. The sustained oscillatory cycle of the resulting solution suggested a possible explanation of the phenomenon by combination of the vortex sheet theory concept and the resonance analysis.