Prediction of flow phenomena, performance and thrust forces of three-stage pump by using URANS

Abstract

This paper describes the results of CFD prediction of performance, internal flow fields and thrust force acting on the impellers of a three-stage centrifugal pump which was provided for the Workshop “Single-&Multistage Pump Flow Prediction”. URANS (Unsteady Reynolds Averaged Navier-Stokes) was applied for the CFD prediction. Parts of the results were already reported by the authors. In this paper, more details are described, especially on the relationship between the changes of the flow fields in the pump and performance of axial thrust characteristics. The effects of axial shift on the performance and axial thrust characteristic are also investigated. URANS calculations were conducted at the design flow (Qd) to a near shut-off condition (10% Qd). The predicted Q-H performance shows a good agreement with the experiments. This pump shows positive slope in the head curve near the shut-off condition. URANS predicted the positive slope in the head curve near the shut-off condition, its flow rate, however, was slightly higher than that of the experiment. The reverse flow between the impeller and the diffuser developed when the flow rate was reduced. The interaction between the reverse flows and the flow in the side-wall gaps (front, back) affects pressure distributions and then axial thrust acts on the impeller. The details of the change of the interaction by flow rate predicted by URANS are described including the effects of axial shift of the rotor. URANS predicted earlier change in the axial thrust characterized by axial shift of the rotor than occurred in the experiments. This discrepancy was caused by interaction between reverse flows and side wall gap flows starting at higher flow than in the experiments.