Controlled Air Jet Blowing for the Homogenization of Compression Bump Air Intake Flows

Abstract

Compression bump engine air intakes play a major role in the development of new fighter aircraft, since, due to their geometrical shape, they contribute to the reduction of radar cross section. In direct competition to Pitot air intakes the compression bump shape has to be designed optimally in order to guarantee high total pressure recoveries by displacing the incoming boundary layer so far outwards that only high momentum flow enters the air intake channel. The objective of the compression bump air intake design and the following air intake channel is achieve the highest possible total pressure recovery at the aerodynamic interface plane (AIP) to the engine, a homogeneous flow distribution with the lowest flow distortion. In most cases certain design Mach numbers, engine mass flows and angles of attack are addressed in the intake design and optimization process. However, angles of attack (AoA) and, equally important, side slip angles (AoS) are changing rapidly during maneuver flights. This results into non uniform and asymmetric onflow in front of the air intake, under certain conditions, in strong asymmetric vortical flow separation. Eventually, all that accumulates to an asymmetrically shifted and concentrated total pressure loss region at the AIP, which has a negative impact on engine performance. Therefore, flow control methods are investigated which allow to symmetrize the flow in front of the air intake again and, thereto, homogenize the flow at the AIP. In this numerical simulation study, controlled jet blowing is used to redirect the asymmetrically onflowing air in front of a generic compression bump engine air intake, correcting the unfavourable flow situation which occurs at high angles of attack and aircraft side slip. Thereto, in this investigation three slit like air vents are artificially incorporated as numerical boundary condition at the side wall of the generic fuselage model. The slits are placed with a lateral offset in front of the compression bump. In order to gain the most effective air jet boundary flow conditions for the most homogeneous onflow conditions at the AIP, a particle swarm optimization (PSO) method has been applied. Two Mach number flow cases, Mach 0.8 and 1.63, have been considered for both the AoA is set to 16 degree and the AoS to 10 degree. Based on the PSO simulation results, the investigation concentrates on the overall effectiveness of this kind of active flow control.