Investigations on the effect of rotational speed on the transport of air-water two-phase flows by centrifugal pumps.

• Gas-liquid two-phase flows were studied in a centrifugal pump. • Effects of the rotational speed were thoroughly studied. • Hysteresis, head degradation, surging, and flow instabilities were considered. • The two-phase flow regimes were recorded and identified using a high-speed camera. • Increasing rotational speed leads to various improvements in two-phase pumping. This study presents experimental and numerical investigations on air-water flows in a centrifugal pump, extending our previous studies. The main objective of the present article is to examine the influence of rotational speed on pump performance. For that purpose, the pump performance was considered and extensively compared for two different rotational speeds, i.e., 650 rpm and 1000 rpm, covering different single and two-phase flow conditions. To allow flow visualization, the impeller and the pump body were manufactured from transparent materials, and a high-speed camera was employed for recording the two-phase flow regimes. The performance of the pump was illustrated and reported for either a constant gas volume fraction or a constant air flow rate at the pump inlet. The desired operating conditions at the inlet were achieved using various predetermined experimental procedures to study the performance hysteresis. Pump surging and breakdown conditions were also considered. Additionally, 3D URANS single-phase numerical simulations were performed to explain additional internal flow details. The moving-mesh approach combined with the k - ω SST turbulence model has been used for that purpose. The simulations agree well with the experiments in most cases. Overall, the results show that increasing the rpm enhances two-phase mixing, which leads to various and significant improvements regarding two-phase pumping performance. [ABSTRACT FROM AUTHOR]