Abstract
The flow field in a hypersonic inlet model at a design point of M = 6 has been studied experimentally. The focus of the current study is to present the time-resolved flow characteristics of separation shock around the cowl and the correlation between the separation shock oscillation induced by the unstart flow and the wall pressure fluctuation when the inlet is in a state of unstart. High-speed Schlieren flow visualization is used to capture the transient shock structure. High-frequency pressure transducers are installed on the wall around both the cowl and isolator areas to detect the dynamic pressure distribution. A schlieren image quantization method based on gray level detection and calculation is developed to analyze the time-resolved spatial structure of separation shock. Results indicate that the induced separation shock oscillation and the wall pressure fluctuation are closely connected, and they show the same frequency variation characteristics. The unsteady flow pattern of the “little buzz” and “big buzz” modes are clarified based on time-resolved Schlieren images of separation shock. Furthermore, the appropriate location of the pressure transducers is determined on the basis of the combined analysis of fluctuating wall-pressure and oscillating separation shock data.
Highlights
Supersonic combustion ramjet propulsion systems have been developed for the future air-breathing hypersonic vehicle
From the view of flow structure [6], the hypersonic inlet unstart is defined as the disgorging of the shock train system in the scramjet engine inlet and isolator
T5 transducers measured a weak second harmonic generation, which indicates that the pressure fluctuation in the cowl area has a wider range of frequencies, which differ from the downstream region. Both the data of the grayscales (Figure 10) of the unstarted separation shock in the Schlieren image and the wall-pressure (Figure 13) indicate the similar trends in the dominant frequency. These results demonstrate that shock oscillations and pressure fluctuations are highly correlated showing the validity and rationale of the grayscale detection method
Summary
Supersonic combustion ramjet (scramjet) propulsion systems have been developed for the future air-breathing hypersonic vehicle. The scramjet flowpath consists of four parts: inlet, isolator, combustor, and nozzle. The inlet is used to capture and compress the incoming hypersonic air flow. For a highly efficient hypersonic airbreathing propulsion system, the inlet should provide high-performance compression with minimum aerodynamic losses produced by shock waves and fluid viscosity. From the view of flow structure [6], the hypersonic inlet unstart is defined as the disgorging of the shock train system in the scramjet engine inlet and isolator. From the point of the inlet performance, if the internal flow changes the flow capturing characteristics of the inlet, the operation condition can be defined as inlet unstart [2,6]
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