Computational Investigation of Flow Over Nose Cap of Closed Impeller of Mixed Flow Centrifugal Pump

Flow turbulence near the suction region and over the eye of a closed impeller may be troublesome during the operation of a centrifugal pump. This article aims to bring out a methodology for minimization of flow turbulence and for providing guidance to suction flow by modifying the surface design of the lock nut into a nose cap of optimized profile. The effects of this modification on the performance parameters of closed impeller of a low head, mixed flow centrifugal pump are presented here. Based on geometric constraints and impeller eye diameter, nose caps of 65mm diameter and various nose tip angles (15-90 deg) and lengths (50-80mm) are evaluated. Parametric studies are carried out via computational fluid dynamics (CFD) analyses using ansys fluent 17.0 as well as experimental investigations to investigate the effects on head, energy consumption, and overall efficiency for flowrates in the range of 0.25-1.5 times the flowrate at best efficiency point (BEP). The estimates of head developed obtained using CFD and experimental studies match within 4.23%. Results confirm improvement in performance parameters like head and overall efficiency due to the reduction of losses and better flow guidance in the suction region. The performance improvement is greatest for the nose cap of 90(0) tip angle and 50mm length at all flowrates.