A novel flow control concept was presented to improve the performance of fix-geometry two-dimensional mix-compression supersonic inlet when the free stream Mach number was lower than the cruising Mach number.This concept is placing a special bypass-slot at the front-end of the second ramp

which can change the configuration of the shock wave system to enhance the performance of the inlet.The numerical results indicate that when the free stream Mach number is smaller than the cruising Mach number

compared with the initial inlet

the flow control can raise the total pressure recovery coefficient and mass flow ratio significantly.Whereas the performance of the inlet declines little at the design point with the bypass-slot shut.In conclusion

the flow control concept is beneficial to the ramjet engine under the speeding up condition.