A model of coupled flow in impeller and volute of a single stage centrifugal pump with interaction of impeller-tongue gap flow

The impeller-volute interaction flow in centrifugal pump is influenced by the flow in impeller-tongue gap. In order to completely understand the mechanism of interaction between impeller-volute flow and impeller-tongue gap flow, a transient three-dimensional numerical simulation of the flow in a single stage centrifugal pump was carried out by applying sliding mesh approach and the standard k-ε turbulence model in CFD, and the derived transient flow data were time-averaged over a period of one blade passing the tongue. The analysis of the flow in the pump revealed that under off-design conditions, a reversed flow with lower pressure at small flowrates below the dutypoint or a stagnation region with higher pressure at high flowrates above the dutypoint appeared in the near tongue region in volute, which enhanced the asymmetric flow in impeller channels. It was consequently considered that the flow in impeller-tongue gap was a superposition of a drag flow by impeller and a pressure leakage flow driven by pressure difference between two sides of the tongue, and the pressure difference was zero at design condition, but increased with the deviation degree of the flow in impeller from the dutypoint. Under smaller flowrates, the gap leakage flow has direction opposite to that at higher flowrates, and affects much the volute flow. In the end, based on the analytical results, a semi-empirical model for the volute flow was deduced by one-dimensional flow continuity, and it may supply a reference for optimizing the flow in volute. © 2020, Turbomachinery Society of Japan. All rights reserved.