Experimental study on dynamic characteristics of shock train in an isolator with different types of incident shocks

Abstract

The hypersonic mixed-compression inlet, operating in an off-design state, can be categorized into low-speed and over-speed regimes based on whether the external compression shock is incident into the internal flow channel. In this study, we investigate the movement process of the shock train within an inlet/isolator under both low-speed and over-speed conditions by generating various incident shocks using wedges installed in a direct-connected ground wind tunnel. Experimental investigations are conducted to examine the dynamic characteristics of the shock train in an isolator subjected to different types of incident shocks at an incoming Mach number of 2.7. The findings reveal that varying levels of backpressure resistance for the shock train are observed with different types of incident shocks. Through the movement trajectory of the shock train leading shock (STLS) and power spectral density analysis, it is found that unilateral incident shocks result in a more intense oscillation process for the shock train with a lower dominant oscillation frequency. The dynamic mode decomposition method identifies different oscillation structures within the unsteady shock train flow field and highlights that dominant mode energy primarily concentrates at the STLS, while its symmetry is influenced by the type of incident shock. Specifically, the symmetric bilateral incident shock tends to promote a higher degree of symmetry in the STLS structure while reducing its oscillation strength; however, when the STLS passes over the reflection point of the incident shock, the rapid upstream movement of the shock train still occurs in this situation, thereby inducing inlet unstart and compromising engine safety.