Effects of the Inlet Flow Conditions on the Tip Clearance Flow of an Isolated Compressor Rotor

Abstract

Numerical investigations on the effects of varying inflow conditions on the tip leakage flow field of an isolated low–speed compressor rotor and the respective rotor tip section cascade were performed at corresponding operation points. Inlet flow variations at each flow rate were obtained by means of varying the boundary layer thickness in such a manner that the non-dimensional integral parameters of the simulated inflow boundary layers were identical for the rotor and cascade. In order to describe the flowfield through the tip gap and its interactions with the incoming flow accurately, a fully–gridded tip gap region was employed. The numerical predictions for comparable inflow conditions agree well with experimental results from previous investigations on the endwall boundary layer separation due to tip clearance flow. It is demonstrated by the simulations that thickening the inflow boundary layer forces the roll-up point of the clearance vortex to move towards the leading edge. By its effects upon leakage flow, varying the incoming boundary layer has a deleterious effect on stall mass flow similar to increasing the tip clearance height. The investigations further reveal a great deal of similarity between the steady state clearance flow in the cascade and the rotor overtip leakage flow.