Stall Margin Improvement in a Centrifugal Compressor Through Endwall Reshaping

This paper presents the results of numerical studies on the effect of endwall reshaping on the performance and stall margin of a centrifugal compressor. The endwall (shroud) of a baseline compressor was reshaped by introducing a convex hump at a location downstream of the inducer where the flow turns from axial to radial direction. The depth of the hump was varied as 3%, 6%, and 9% of the local impeller blade height. The impeller was also locally reshaped to match the shroud, maintaining the baseline tip clearance. Other geometric parameters of the reshaped impeller were kept same as those of the baseline impeller. An implicit, coupled, density based solver (ANSYS FLUENT) was used with first order upwind discretization scheme. The local reshaping of the endwall and impeller blades showed a positive tendency of increase in compressor stall margin without any appreciable reduction in efficiency. Endwall reshaping of 9% of the local blade height resulted in reducing the stall mass flow rate by 6.4 % of the baseline stall flow rate. Further, the peak total pressure ratio showed a marginal increase of 0.8%. Reshaping of the endwall was observed to cause local acceleration of the flow, thus weakening separation bubble and delaying inception of stall.