Image analyses of supersonic air-intake buzz and control by natural ventilation

Intake buzz was initiated on a typical two-dimensional supersonic air-intake model at various supersonic Mach numbers up to 3 by gradually changing the back pressure from supercritical to subcritical operating condition in a wind tunnel. Schlieren pictures from a still camera and a high-speed camera were recorded. Analyses of individual high-speed images of the unvented intake were carried out to locate the time-dependent positions and velocities of the ramp shock around the cowl lip. The displacements of the shock indicate sinusoidal oscillations with dominant frequency of 102.4 Hz, close to that obtained from unsteady pressure measurements. Phase trajectories of shock position based on image analyses indicate that the shock oscillations have limit cycle type oscillation, typical of nonlinear dynamic systems. Natural ventilation of the intake was found to be extremely effective in increasing the total pressure recovery, suppress buzz oscillations and in delaying the onset of buzz by preventing the upstream propagation of disturbances through passive bleeding of the internal boundary layer.