Validation and Parametric Study of Supersonic Air Intake

Abstract

The current study was carried out on behalf of GKN Aerospace as a Master's thesis at Chalmers University of Technology. The Department of Propulsion Engineering at this company wished to develop a deeper understanding into the performance of supersonic engine intakes and to relate this to the in uential physical notions and geometry alterations. The ultimate objective was to obtain a CFD model to study the effects of key variations of geometrical and physical parameters on the aerodynamic performance. This model was initially to be validated on a model scale against the results of wind tunnel tests. The specific means by which this validation was done was to compare the mass ow and total pressure recovery at the outlet of the intake, as predicted by wind tunnel tests and by the CFD model. The results of the validation study show that despite the two-dimensional geometry of the intake, the ow in the interior of the intake is highly three-dimensional. This is mainly attributed to the separation in the subsonic diffuser, induced by shock waves and end-wall, turbulent effects. This has highlighted distinct di erences in the means by which the global, gross effects of total pressure recovery is estimated in wind tunnel tests as compared to the model. Nevertheless, disregarding from the explicable differences, a sound model was achieved. The secondary objective was to scale this generic model intake to a real size, to meet the mass ow requirements of a typical engine. As the scaling was performed, alterations to the external compression ramp geometry was implemented. This was done in order to investigate the global e ects of having an isentropic, continuous-curve type ramp as compared to a discrete, two-step ramp. As the parametric study was carried out, it was concluded that the effect of having a discrete ramp was mainly that of reducing the mass ow swallowed by the intake. While having comparable levels of global total pressure recovery, the discrete-ramp geometry featured the positive effect of limiting ow separation and distortion in the diffuser section. This effect was attributed to the reduction in velocity and momentum of the ingested mass ow, due to less efficient external compression and increased mass ow spillage. Finally, aerodynamic performance of the large-scale intake was assessed in terms of aerodynamic drag forces and pitch torque. On the basis of the conclusions formed in this project, some recommendations for future work were given.