Experimental Investigation of Instability of a Supersonic Mixed Compression Air Intake

An extensive experimental study has been conducted to investigate the performance and stability of a supersonic axisymmetric mixed compression air intake. The intake has been designed for a free stream Mach number of 2.0. However, tests were conducted for free stream Mach numbers of 1.8, 2.0, and 2.2. This investigation is aimed at studying effects of Mach number and back pressure on the intake flow stability during the buzz phenomenon. Further, the effect of acoustic resonance on the Buzz frequency has been investigated. Buzz phenomenon is defined as the shock oscillation ahead of the intake that may occur when the intake mass flow ratio reduces. Results show that the stability margin reduces when the free stream Mach number increases. In addition, reducing the free stream Mach number and increasing the back pressure cause the oscillation frequency to increase. The main cause of instability start is flow separation on the compression ramp and two ranges of frequency of buzz oscillations are obtained, range of 100 Hz for flow instability for Mach numbers of 1.8, 2.0 and 2.2, and range of 475 Hz for flow instability in Mach number of 1.8. For both cases, the spatial domain of buzz oscillations covers the entire intake length. Further, these low and high frequency ranges have significant conformity with the zeroth-order and first order of the acoustic resonance frequency, respectively, that increase the probability of existence of acoustic resonance driving the buzz oscillation.