Fluidic Nozzle to Improve Transonic Performance of Hypersonic Vehicle

Use of fluidic injection of high-pressure air is proposed to improve a hypersonic vehicle's installed nozzle performance and eliminate undesirable pitching moments at off-design, transonic flight conditions. Hypersonic flight vehicles are typically designed with a high expansion ratio Single Expansion Ramp Nozzle (SERN) for a design point at high Mach number flight conditions. However, at low Mach number (transonic) flight, the nozzle is over-expanded, resulting in low, sub-ambient pressures acting on the expansion ramp surface. These sub-ambient pressures cause increased drag, reduced performance, and large pitching moments. The loss in net thrust-minus-drag performance may be as high as 25% throughout much of the transonic flight regime. The corresponding pitching moment is large and must be overcome by increasing the size of the vehicle's control surfaces. The proposed fluidic injection concept eliminates these problems and improves the overall vehicle performance by injecting high-pressure air into the nozzle to induce a flow separation, thereby increasing the pressure on the SERN ramp. The objective of this Phase I program is to demonstrate the feasibility of fluidic injection to improve off-design performance of hypersonic aircraft at transonic speeds, culminating in the preliminary design of an experimental rig to be used for Phase II testing.