Design and characteristics of supersonic inlet controls for minimizing inlet unstarts.

A near-isentropic supersonic inlet, at Mach 2.2, has been designed to give enhanced recovery and thus increased range for a supersonic transport aircraft. In such a design a mixed compression inlet design is typically used. Enhanced recovery of 97% in total pressure is achieved by reducing the unstart-tolerance of the inlet and by an efficient boundary layer control mechanism. Thus the resulting inlet design has reduced stability to unstart in the face of atmospheric and engine-born disturbances, necessitating active control. An active stabilization bleed system is introduced that recovers the disturbance-rejection capabilities required of modem inlets. The bleed system requires 4% steady state bleed and up to 6% additional unsteady bleed for active stabilization. Two separate physical mechanisms for unstart are identified, and active control algorithms to prevent these forms of unstart are designed and demonstrated using quasi-l-D and 2-D unsteady Euler simulations. The CFD codes used have been optimized for accurate propagation of disturbances, to insure that physical mechanisms are correctly captured. The resulting actively stabilized inlet can withstand worst-case empirically determined (by NASA) atmospheric disturbances such as flight velocity, temperature, and angle of attack perturbations consistent with atmospheric flight.