Experimental Investigation of the Unstart Process of a Generic Hypersonic Inlet

To provide information for the detection, prediction, and control of the inlet unstart, the entire process from a started status to an unstarted status of a generic two-dimensional hypersonic inlet is studied experimentally at Mach 5. The movement of a flow plug at the exit of the duct is used to gradually increase the throttling to simulate the unstart process caused by the excessive heat release in the combustor. Simultaneous high-speed schlieren imaging and dynamic surface pressure measurements are used to record the unsteady flow structures and surface pressures of the unstart process. According to the internal and external flows, the unstart process can be divided into four stages, namely, shock train in the combustor, shock train in the isolator, separation bubble in the throat, and unstart. The transient flow patterns of each stage are substantially different and the corresponding dynamics pressures also have prominent time-frequency features, which make the detection and prediction of the inlet unstart based on dynamic pressures possible. Since the sensor placed at the end of the top surface of the inlet contract part, marked by C1, obtains the most abundant time-frequency characteristics which can be used to discern the different stages of the inlet unstart process, the location where it stays is regarded as the first choice for sensor placement to construct a practical inlet-status-monitoring system.