Experimental investigation of the interaction between a curved-surface jet and the mainstream on an airfoil at Mach 8

The accumulation of aerodynamic heat at the rudder shaft of a hypersonic vehicle will reduce the vehicle's aerodynamic performance. This paper proposes a trailing-edge curved-surface jet with longitudinal characteristics to solve this problem. We used high-speed photography and force measurement techniques in the experiment. The results show that the interaction between the expansion wave formed by the curved surface jet and the hypersonic flow will generate an oblique shock wave and finally form a unique flow structure. The oblique shock wave in the new flow structure is the key to realizing the rudderless flight, and it can linearly control the pitching characteristics of the hypersonic airfoil. That is, it can linearly control the attitude of the model. The diffusion angle of the jet has a significant influence on this oblique shock wave. Experiments show that the dimensionless parameter pressure ratio PR and the jet diffusion angle roughly present a linear relationship. Therefore, there is approximately a linear relationship between PR and the flow control effect of the curved-surface jet. When the PR is within 90∼250, the curved-surface jet can increase the pitching moment coefficient by 0.033∼0.132. The dynamic mode decomposition results show that expansion wave, jet instability, oblique shock wave, and boundary layer are the dominant factors affecting the new flow structure. This paper proposes a new theoretical model to reveal the flow control effect and the physical mechanism of the curved-surface jet. The results provide an experimental and theoretical basis for realizing rudderless hypersonic vehicles.