Dual-mode scramjet engine may suffer unstart because of a large enough upstream or downstream pressure disturbance.Unstart would dramatically reduce the thrust and could compromise the stability and safety of the vehicles

so it is necessary and important to investigate the effective control methods.Fifth-order characteristic-wise weighted essentially non-oscillatory (WENO) scheme and third-order total variation diminishing (TVD) Runge-Kutta (R-K) method were applied to solve the three-dimensional Navier-Stokes (N-S) equations

to explore two passive control methods using trips and passive suck/blow respectively

and to explore corresponding control effect on the hypersonic flow separation caused by shock wave/boundary layer interaction induced by a fin.The results show that the vortex in flow direction induced by trips affects the flow separation structures evidently.The second separation and reattachment lines almost disappear.Control method employing passive suck/blow balances the pressure between the separation and reattachment areas and reduces the pressure gradient which depresses the separation structures.