Aerodynamically controlled expansion nozzle for short takeoff and vertical landing aircraft

The aerodynamically configured expansion nozzle concept featuring a boundary-layer control step for short takeoff and vertical landing aircraft was discussed. It is suggested that the step separates the boundary layer from the divergent flap, relieving overexpansion loss through an aerodynamic tailoring effect. It was found that a minimum step size of 1.1 will induce flow separation and relieves overexpansion loss at the hover condition of nozzle pressure ratio (NPR) = 2 for the JSF nozzle with step size of 1.3. The results show that a step size of 1.2 produces undesirable step drag at higher NPR conditions.