Effects of Slotted Hub and Casing Treatments on Compressor Endwall Flow Fields

Abstract

An experimental investigation was carried out to examine the influence of a rotating slotted hub treatment on a compressor stator passage endwall. Detailed mapping of the three-dimensional unsteady velocity field near the hub was done for a smooth hub and a hub having axial skewed slots. With the smooth wall, the velocity measurements indicate that a large region of blockage occurs near the rear of the blade passage. This blockage is seen to be associated with the hub endwall rather than either the suction surface or the pressure surface of the blade. With axial skewed slots, the blockage is markedly decreased, the stalling flow coefficient is reduced, and the peak pressure rise greatly increased. Due to the axial (rear-to-front) flow in the slots, there is a region of fluid removal (from the endwall) near the rear of the passage and a strong fluid injection, or jet, near the front. The data appear to show that this flow removal is an important part of the effect on stall margin found with hub and casing treatment. Furthermore, the data indicate that it is the (dissipation of the) high velocities in the jet that is the prime source of the efficiency reduction associated with this treatment.