Semiempirical theory of the generation of discrete tones by a supersonic underexpanded jet flowing over an obstacle

Mechanism of self-oscillations in a supersonic jet impact onto an obstacle 1. Obstacle with a spike

“…After that, they interact with the external boundary of the jet, propagate in the downstream direction toward the obstacle, and are enhanced in the mixing layer. It was noted [4,8] that these disturbances have an entropy-vortex character. However, the mechanism of their action on the separation region differs from the mechanism proposed in [4,8].…”

“…It was noted [4,8] that these disturbances have an entropy-vortex character. However, the mechanism of their action on the separation region differs from the mechanism proposed in [4,8]. It was assumed in [4,8] that these disturbances directly affect the shock wave reflected from the obstacle and the radial jet spreading over the obstacle.…”

“…However, the mechanism of their action on the separation region differs from the mechanism proposed in [4,8]. It was assumed in [4,8] that these disturbances directly affect the shock wave reflected from the obstacle and the radial jet spreading over the obstacle. The results of the present calculations show that these disturbances impinge onto the external edge of the separation region and allow the supersonic flow to penetrate into this region, similar to that in Problem 1.…”

“…Oscillations at a discrete tone in various cases of impingement of an underexpanded supersonic jet onto bounded and unbounded obstacles were considered in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Two mechanisms of the emergence of oscillations were proposed: the mass-flow-rate mechanism with an internal feedback [1,[11][12][13][14] and the mechanism with an external feedback through the gas surrounding the jet [2-5, 8, 9].…”

“…The internal acoustic relationship is ensured by compression and expansion waves propagating between the shock wave and the obstacle. The external feedback mechanism proposed in [8,9] acoustic model [2,3]. In this case, the feedback is provided by acoustic disturbances generated by the radial jet spreading over the obstacle.…”