Buzz Cycle Description in an Axisymmetric Mixed-Compression Air Intake

摘要

Buzz phenomenon is shock oscillation ahead of the supersonic air intake when its mass flow rate is decreasing at off-design condition. The buzz onset and the buzz cycle of an axisymmetric mixed-compression supersonic intake have been experimentally investigated through pressure recording and shadowgraph flow visualization. The intake was designed for a freestream Mach number of 2.0; however, tests were conducted for M-infinity = 1.8, 2.0, and 2.2. All tests were performed at 0 deg angle of attack. Results show that there is a strong relation between the acoustic characteristics of the intake and the buzz fluctuations. This relation causes a new pattern for the buzz oscillations, large-amplitude oscillations with large frequency, that has features of both little buzz (Ferri-type instability) and big buzz (Dailey-type instability). Flow separation caused by the shock-wave/boundary-layer interaction and acoustic compression waves are the most important driving mechanisms in the buzz cycle. Both amplitude and frequency of the buzz oscillations vary as the backpressure is varied. As the freestream Mach number is increased, the dominant frequency of the buzz oscillations is decreased.