Finite Element Computation of Buzz Instability in Supersonic Air Intakes

Abstract

An intake is a duct designed to provide sufficient amount of air at low speed to the engine face, at high efficiency and with little distortion. The physical shape of the intake is fundamentally the same as that of a convergent-divergent nozzle. Inlets may have different shape and size depending on the speed of the aircraft. An inlet must be able to sustain high pressure that exists at the engine face. Supersonic intakes may be associated with flow instability at relatively high back pressure at the engine face. The buzz instability involves periodic filling and discharge of the plenum chamber, complex shock-boundary layer interaction, shear layer/slip stream-boundary layer interaction, transient shock movement and flow separation. It adversely affects the mass flow entering the engine and may lead to combustion instability, engine surge and flame out. It can also lead to deterioration of the performance of propulsion system, thus causing catastrophic loss in thrust. In this article we describe our computational efforts in understanding flows in intakes of supersonic vehicles. The flow instabilities in a Y-intake and mixed compression intake are studied numerically via a stabilized finite element method.