EFFECT OF EXIT BLADE ANGLE, VISCOSITY AND ROUGHNESS IN CENTRIFUGAL PUMPS INVESTIGATED BY CFD COMPUTATION

Abstract

It has long been known that the exit blade angle plays a very important role in the performance of a centrifugal pump handling water or viscous oil. The effect of exit blade angle on the performance and flow of centrifugal pumps is usually investigated experimentally. However, due to the high cost and limited data that can be obtained by experiment, currently there is a great need for this effect to be studied numerically by means of computational fluid dynamics (CFD). At present, extensive comparisons between experiment and simulation regarding the performance of viscous oil and flow in centrifugal pumps with different exit blade angles are not available. Hydraulic performance and flow details in the impeller and the volute of a centrifugal pump with an exit blade angle of 44◦ were investigated numerically with the CFD code Fluent R, using water and viscous oil as the working fluid, respectively. The effect of exit blade angle was then elucidated by comparing the performance and flow with that of a pump with an exit blade angle of 20◦. It was determined that the results for the performance and flow obtained by means of CFD were in qualitative agreement with the observations. The sudden-rising-head effect is dependent on roughness and viscosity. The unstable zone in the theoretical head curve of the impeller at a low flow rate was attributed to the strong reaction of the volute to the flow in the vicinity of the impeller exit. The flow in the impeller with a large exit blade angle was subject to separation near the blade pressure side, however, a large exit blade angle helped improve the pump performance of viscous oil.