Research On Flow Characteristics Of Some Typical Hypersonic Shock Wave Interactions

Extremely high pressure and heat flux caused by shock wave interactions in the engine cowl lip region are an issue worthy of concern in the design of air-breathing hypersonic vehicles. Shock interactions can generate very complex flow patterns, causing flow separation, reattachment, and supersonic jet impingement which have the potential to result in flow unsteadiness and intense localized heating that might jeopardize the structural integrity. Therefore, the investigation of shock-shock interaction is of significant importance not only in the aero-thermodynamic design of hypersonic vehicles, but also in understanding the mechanism of the compressible flow.This dissertation describes an experimental and numerical study of shock wave interaction on blunt leading edges representative of cowls of hypersonic inlets. The experimental work was carried out in a shock tunnel. Numerical simulations were conducted using the finite volume method. Flow patterns and surface pressure and heat flux distributions were obtained and analyzed. Furthermore, the effects of the external geometry of the leading edge and the freestream conditions on the shock interaction were evaluated. The primary objective of this study is to obtain a better understanding of the mechanisms of the unsteady characteristics and the attendant surface pressure and heat flux distributions. The results and conclusions are presented as follows:1. A numerical investigation of the hypersonic type IV shock interaction was carried out, focusing on the effects of viscosity, impinging shock location, shock strength and the blunt body geometry on the unsteady characteristics and the surface heat flux and pressure loads. The results show that the flow can be either steady or unsteady depending on the variations of the above mentioned factors. The inviscid features dominate the shock interaction flow. With the increase of the shock strength and the bluntness of the body, the pressure and heat flux rates increase and the Strouhal number that depends on the shock standoff distance decreases. Properly choosing the geometry of the blunt body may suppress the oscillation and reduce the fluctuating peak surface heat and pressure loads effectively. Moreover, the shock wave oscillation may weaken by decreasing the freestream Mach number.2. The effect of a forward-facing cavity on the unsteady behavior of the hypersonic type IV shock interaction flow over a circular cylinder were investigated experimentally and numerically. Using high speed schlieren photography and high frequency pressure transducers the detailed flowfield structure and pressure at the base of the cavity were obtained. Agreement between the experiments and computations is good for the flowfield structure and the oscillation frequency. The results show that the type IV shock interaction can be either steady or unsteady depending on the location of the supersonic jet impingement. The interference between the supersonic jet and the forward-facing cavity plays a key role in the shock wave oscillations. Two different oscillation modes were observed:namely a high frequency forward-backward mode and a low frequency up-down mode. Furthermore, experimental results from cylinders with different length-to-diameter ratios indicate that the three-dimensional effects have a significant impact on the oscillation.3. An experimental and numerical investigation of shock wave interactions on a V-shaped blunt leading edge which is commonly designed in hypersonic inlets was carried out, focusing on the effects of the geometry of the leading edge and the freestream Mach number. Good agreement between experimental schlieren images and wave patterns calculated by numerical simulations was obtained. The shock interaction in the crotch region creates complex wave patterns including regular and Mach reflection configurations and an uneven distribution of the surface heat flux. Extremely high heat flux caused by shock wave/boundary layer interaction, shear layer attachment, or the impingement of supersonic jets occurs over a narrow region. Numerical results indicate that under certain conditions the local surface heat flux can be up to 24 times the stagnation point value computed from the Fay and Riddell theory. Moreover, increasing the leading edge bluntness may have a significant negative effect on the thermal protection of the crotch due to the shock interaction. The unsteadiness of the shock interaction on the V-shaped leading edge was preliminarily studied, which might be caused by the instabilities of the supersonic jet and the shear layer.