Response of Shock Train to High-Frequency Fluctuating Backpressure in an Isolator

Abstract

Schlieren images and unsteady pressure measurements were collected to explore the response of a shock train to a high-frequency fluctuating backpressure in an isolator. High-frequency excitations (between 105 and 225 Hz) were applied in the downstream of an isolator, thus leading a forced shock train oscillation. The experimental results show that the fundamental frequency of a shock train oscillation is very close to the excitations, and the shock train motions can be judged by pressure measurements. The whole isolator can be divided into three parts, including the undisturbed zone, the shock train oscillation zone, and the backpressure-affected zone. Different cases of forcing frequencies were studied, and it is found that the amplitude of the shock train oscillation increases with the decreasing excitation frequency. Moreover, the most upstream position of shock train motions is not located at the place where the maximum standard deviation occurs under fluctuating backpressure condition. Thus, the maximum standard deviation method can no longer be used for shock train leading edge detection. Actually, the most upstream position of the shock train leading edge is located at the place where the excited frequency content disappears or the place where the oscillation amplitude decreases to near zero.