Design and Experimental Verification of a Scram-Jet Inlet in Frame of ESA's LAPCAT Program

Kurzfassung

In 2005 ESA started a research program LAPCAT (Long-Term Advanced Propulsion Concepts And Technologies) to identify and assess propulsion technologies to reduce the duration of long distance flights. One selected vehicle, the LAPCAT M8, is proposed to feature an RBCC (Rocket Based Combined Cycle) engine. Starting from Mach 4 up to the cruise Mach number of 8 it is propelled by an air-breathing SCRAM-jet. The subject of this paper is the design and the wind tunnel verification of the air inlet for this vehicle. Because of the vehicles forebody shock, the inlet is exposed to an oncoming flow of about Mach 6. It then has to compress a sufficient air mass flow up to supersonic combustion conditions. To meet this requirement, a planar, non self-starting inlet contour was designed by inviscid CFD tools. This contour features two external compression ramps, followed by a cowl that generates an internal shock train. To reduce boundary layer separation induced by the cowl shocks, a mixed bleed/diverter channel was integrated. The bleed keeps the separation bubble contained and prevents the inlet from choking. Based on the designed inlet, a scaled wind tunnel model was built. It is equipped with moveable ramps in order to start the inlet. During the test runs, a throttle mounted downstream the inlet simulates the counter pressure of the combustion and measures the mass flow. An integrated window and several static pressure taps allow to monitor the internal compression process. Two Pitot probes combined with static pressure data at the inlet exit are used to predict the pressure recovery and the Mach number. A first test campaign at the H2K blow down facility proved the functionality of the designed inlet. At the design configuration the inlet met all its requirements. Several tests at off design conditions, i.e. at a lower amount of bleed or at different angles of attack and yaw provided valuable information about it’s off design operation and inlet flow topology.