Lip Stall Suppression in Powered Intakes

This work describes a computational study into lip stall in subsonic civil aircraft intakes and its alleviation by action of the fan. Beyond a certain flow incidence, the lower lip of a civil aircraft intakes stalls. This phenomenon causes entropy and vortical distortions at the fan face. Consequently, it has detrimental effects on vibration levels and performance of the low-pressure compressor system. The most important parameters influencing lip separation are the flight Mach number, the Reynolds number, and altitude. Fully three-dimensional simulations have been performed on a flight intake in current service for which the experimental data are available. Steady and time-resolved simulations have been performed. Distortion coefficients have been evaluated as functions of incidence and have been compared with experimental results. A comparison between an isolated intake and a powered intake shows that the fan stage has the beneficial effect of increasing tolerance to flow incidence and decreasing distortion. The study also shows that, whereas the total pressure deficit at the fan face is a function of incidence, the flow can be represented by a relatively simple vortex system, the strength of which is independent of incidence.