Computational Simulation of Shock Oscillation Around a Supersonic Air-Intake

Unsteady flow around an external-compression air intake was investigated numerically. Our attention was focused to shock oscillation, which is known as ‘buzz’, in subcritical operation. We used a two-dimensional model consisting of a wedge and a subsonic diffuser. A slit was opened for natural bleed at the entrance of the subsonic duct. The wedge angle was 10 degrees. The free stream Mach number was 1.64. Compressible viscous flow around the model was calculated using UPACS (Unified Platform for Aerospace Computational Simulation) developed at JAXA (Japan Aerospace Exploration Agency). We successfully simulated a series of flow pattern (supercritical, critical, and subcritical operations) by changing the intake mass flow rate. In the subcritical operation, multiple dominant frequencies were found in the pressure fluctuation with the buzz. Low-frequency component was caused by the acoustic resonance of the subsonic diffuser. On the other hand, highfrequency component was generated by the periodic flow separation on the wedge. This phenomenon was caused by the periodic suction of the separated air through the slit. The high-frequency component disappeared when the diffuser length was long. The natural bleed slightly suppressed the pressure fluctuation in the subsonic diffuser in a constant mass flow rate through the diffuser.