Effect of secondary-jet on supersonic Coanda jet

The “ C μ-stall” phenomenon of supersonic Coanda jet is one of the difficult problems to be solved in circulation control technology. In this paper, the circulation control of supersonic jet under high-subsonic flight state is studied. The “ C μ-stall” phenomenon of supersonic Coanda jet is deeply explored. In this paper, it is found that there is the first “ C μ-stall” phenomenon before the periodic detachment of the jet. This phenomenon will also lead to a sudden drop of lift, but it will not cause the jet to detach from the Coanda surface. The first “ C μ-stall” is the main factor limiting the effect of supersonic circulation control. A scheme of using staged jet to delay “ C μ-stall” phenomenon and improve the lift increasing effect of circulation control airfoil is proposed. The results show that the secondary-jet can effectively delay the “ C μ-stall” phenomenon and increase the maximum lift coefficient from 0.4986 to 0.5763. The influence of secondary-jet on supersonic Coanda jet (main-jet) can be divided into the influence on its expansion degree and the influence on its attachment distance. The secondary-jet with appropriate strength can not only increase the expansion degree of the main-jet but also prolong the attachment distance of the main-jet, so as to obtain a higher lift coefficient. Finally, taking the lift coefficient as the optimization objective, this paper uses the back propagation (BP) neural network to optimize the mass flow rate combination of the staged jet scheme and improves the maximum lift coefficient to 0.5821.