Effects of unsteady oblique shock wave on mixing efficiency of two-dimensional supersonic mixing layer

Scramjet is the key technology to achieve long-endurance and supersonic flight in the future. With air flowing through the interior of a Scramjet in milliseconds, the rapid mixing of fuel and air becomes one of the great challenges of engine design. Among the various methods of improving fuel-air mixing, shock wave enhancement is an effective technical approach. Based on this, a new method is proposed in this paper to enhance the mixing efficiency of the supersonic mixing layer by using unsteady shock wave. The feasibility of the method is verified by comparing the effects of three conditions on the mixing efficiency of the mixing layer, which are shock-free mixing layer, steady shock/mixing layer interaction, and unsteady shock/mixing layer interaction. The shock wave structures and vortex structures in the three conditions are compared and the vorticity and turbulence intensity are calculated. The results indicate that the shock waves have a significant effect on the mixing layer, especially the unsteady shock. The unsteady shock will cause periodic changes in the shock wave structures and the direction of mainstream flow. Moreover, the shock waves will increase the averaged vorticity at the interaction point and the unsteady shock can greatly enhance the evolution of the vortex structures. The periodic changes of the flow field will cause the oscillation of the mixing layer, resulting in an increase in the averaged vorticity and its fluctuation range of vertical distribution. Furthermore, the unsteady shock wave can significantly increase the turbulence intensity of the mixing layer, and the contribution of the oscillation to the turbulence intensity will counteract the reduction caused by the compression effect of the shock wave. In conclusion, the unsteady shock waves can enhance the mixing efficiency more effectively.