Two-stage growth mode for lift-off mechanism in oblique shock-wave/jet interaction

Abstract

The lift-off flow of the supersonic streamwise vortex in oblique shock-wave/jet interaction (OS/JI), extracted from a wall-mounted ramp injector in the scramjet, is studied through the large-eddy simulation method. The shocked helium jet deforms into a pair of the streamwise vortex with a co-rotating companion vortex. The trajectory of the streamwise vortex center is lifted by the shock interaction. Based on the objective coordinate system in the frame of oblique shock, it is found that the nature of the three-dimensional lift-off structure of the OS/JI is inherently and precisely controlled by the structure kinetics of a corresponding shock bubble interaction (SBI). The striking similarities of both qualitative and quantitative results between the OS/JI and the SBI support the proposition that the lift-off of the streamwise vortex is the result of an underlying two-dimensional vortical motion. By combining the first-stage linear growth mode of Richtmyer-Meshkov instability with the second-stage vortex formation mode, a two-stage vortex propagation model suitable for the SBI is proposed and validated. The lift-off growth of a shocked jet in the OS/JI concerned and in the wall-mounted ramp injector cases from the literature is well explained under the two-stage vortex propagation model of SBI. This model further predicts that increasing ramp compression shows little effect on elevating the streamwise vortex for higher free-stream Mach numbers (Ma > 5). In comparison, evident lift-off may occur for lower Mach numbers (Ma < 3.5), which offers the new way for the preliminary design of a streamwise vortex-based ramp injector in the scramjet.