Stall margin improvement of a centrifugal compressor utilizing various stepped tip gap configurations

Aerodynamic performance of a centrifugal compressor is investigated under various casing treatment configurations of stepped tip gap type, numerically. This technique is introduced as an effective method for improvement of compressor stall margin and consequent enhancement of the compressor overall performance. In this respect, flow field within the proposed compressor was simulated by solving the Navier-Stokes equations utilizing the well-known k- turbulence model. Different geometries of the compressor stepped tip gap were examined to be able to obtain the optimum configuration. Results of velocity contours and streamlines patterns on various azimuthal and meridional planes showed that the stepped tip gap can weaken the tip leakage flow strength and reduce the blockage to the main stream near the casing. Hence, it can be concluded that using stepped tip gap can extend the stable operating range of the compressor and delay the occurrence of stall phenomenon. For small clearances, stepped tip gap was found to improve the stall margin of the proposed compressor at different rotor speeds without any negative effects on its efficiency, except to high flow conditions. But, inclusion of the stepped tip gap with large clearances tends to increase the stall margin with considerable reduction in the compressor efficiency.