Shock Train Leading Edge Detection Method under the Condition of Steady Back Pressure and Fluctuating Back Pressure

In this paper, the shock train in the isolator is taken as the research object, and the method of detecting the leading edge position of the shock train during self-excited oscillation and forced oscillation is studied by conducting the wind tunnel test. A steady-state throttling system and a fluctuating throttling system are designed to apply the required steady-state and fluctuating back pressure downstream of the isolator. Then, the four methods of pressure ratio method, pressure difference method, standard deviation method, and Fast Fourier Transform (FFT) analysis method are used to detect and study the position of the shock train leading edge under steady and fluctuating back pressure to verify their applicability. The results show that under the condition of steady-state back pressure, the four methods can get effective results, and the results are consistent. Under the condition of fluctuating back pressure, the pressure difference method could not give effective results, but the other three methods could give effective and consistent results. And the results of the standard deviation method and the Fast Fourier Transform analysis method are similar in image and principle.