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.
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