Flow Control Methods Based On Shape Memory Alloy For Hypersonic Inlets

Hypersonic inlet is an important component of a scramjet. The overall performance of a scramjet, and even the vehicles, is largely dictated by aerodynamic performance of the hypersonic inlet. Commonly, since the hypersonic inlet has a wide operating Mach number range, it is hard to give overall consideration on the inlet performance at design and offdesign conditions. Thus, to avoid the performance penalties at offdesign conditions, the control of the external shock system and the shock/boundary layer interaction in the duct is needed. As the technology developing, the Shape Memory Alloy shows significant potential in hypersonic inlet flow control. This paper investigates the control method and its key issues based on the Shape Memory Alloy in hypersonic inlets.According to the control demand of external shock in hypersonic inlets, the shock control method based on the partial variable ramp surface is investigated, firstly. The design method that obtains the shock shape by the curved ramp surface is obtained. Furthermore, the inverse design method which gets the curved ramp surface from the shock shape is also brought forward. Based on these methods, the two-dimensional bump on inlet ramp surface to control the external shock is studied and the design principles of the surface bump are obtained.The cowl shock/boundary layer interaction under the effect of corner expansion waves in practical hypersonic inlets is investigated by both theoretical analysis and computational method. Four types of shock/expansion wave interaction process exist when their relative position changes are found. While different interaction process dominates the flowfiled, the expansion waves may bring different effects on the shock/boundary layer interaction. According to the characteristic of the interaction process, the range in which the expansion wave brings positive effect on the shock wave/boundary layer interaction and suppresses the boundary layer separation is obtained.The control method of the shock wave/boundary layer interaction based on a variable bump is brought forward and investigated by both experimental and computational methods. The results show that the shock wave/boundary layer interaction in finite duct generates complex three-dimensional flow structures with significantly swirling nature, which will substantially deteriorate the performance of hypersonic inlets. Then, the controlled case demonstrates that the shock-induced flow separation can be effectively reduced by the coupling of the pre-compression effect and the acceleration effect of the bump. In addition, a two-dimensional bump with a height lower than local boundary layer thickness is introduced to control the multiple cowl shock/boundary layer interactions in a simplified hypersonic inlet. In order to get the better control effect, the incident shocks should impinge on the convex surface of the bump. A well-designed bump can suppress the serious cowl shock/boundary layer interactions effectively in the entire operating Mach number range of the inlet and improve the duct total pressure recovery.The flowfield downstream of the microramp contains rather complex flow structures. The wake region and the vortex induced by the microramp are the two important types of flow patterns downstream of the microramp. However, the traditional microramps cannot suppress the separation induced by the shock/ boundary layer interaction in the duct with finite width effectively. Therefore, a type of highly swept microramps with large chord ratio and small incidence angle is brought forward and investigated. By the precompression effect, the dividing effect, the obstructing effect and the energizing effect, the highly swept microramps show good control capability on the shock/boundary layer interaction. In addition, the efficiency of the control method for different shock impingement positions is obtained, indicating that the separation can be well controlled when the shock impinges on the aft part of the highly swept microramps.At last, a variable hypersonic inlet is designed to validate the flow control method based on the Shape Memory Alloy. Combined with the inverse deformation method and repeat training method, the Shape Memory Alloy plate with perfect deflection and high geometry recovery speed is obtained. Therefore, the self-adaptation variable ramp, automatic surface bump and highly swept microramps made by the Shape Memory Alloy are achieved. With the help of Schlieren technology the profile of these devices during their transforming process are obtained and the flowfields under control are also got by computional method. The computional results show that the inlet performance increases significantly under the control of these flow control devices based on the Shape Memory Alloy.