Impact of blade twisting and tip clearance on centrifugal pump performance under air–water two-phase flow

Abstract

The performance characteristics of a centrifugal pump were investigated experimentally for different conditions of air–water two-phase flow. A 3D semi-open impeller (with twisted blades) and a geometrically similar 2D semi-open impeller (with straight elliptical blades) were employed to compare the pump behavior using each of them, revealing the influence of the blade twisting. Additionally, the effect of the tip clearance gap on the performance of each impeller was investigated by employing either a standard or an increased gap. A rotational speed of 1450 rpm was set for all experiments. The performance of the pump was reported and described for either a constant gas volume fraction or a constant air flow rate at the pump inlet. Possible hysteresis effects were studied by approaching the desired operating conditions using different procedures. The head degradation behavior, the pump surging conditions, and the flow instabilities were considered as well. The two-phase flow regimes were recorded and identified for all the considered cases using a high-speed recording system. The results show that for single-phase flow, both impellers perform similarly, with the 3D impeller showing slight advantages at part-load and the 2D impeller excelling at near-optimal and overload conditions. For two-phase flows with high gas volume fractions, the 3D impeller maintains better performance at overload, while the 2D impeller performs better at part-load conditions. Increasing the gap slightly improves performance for gas volume fractions between 5% and 7% in both impellers. Additionally, the 2D impeller demonstrates a stronger ability to suppress and delay surging and flow instabilities compared to the 3D impeller, making it preferable for applications requiring stable operation across a range of gas volume fractions and load conditions.