Numerical analysis of the formation mechanism and suppression method of the reverse flow in a semi-open centrifugal pump

Abstract

Reverse flow has a detrimental effect on the stable and safe operation of centrifugal pumps. To study the formation mechanism and suppression of the reverse flow, a semi-open centrifugal pump with circumferential groove in the shroud was simulated. Then, the flow field and pressure fluctuation were analysed. The absolute flow angle at the blade inlet nearing the shroud was close to 180° because of the joint action of the leakage flow and blade inlet impact under low flow rate. This phenomenon resulted in the formation of a low-speed region and the reverse flow and low-frequency pressure fluctuation. The circumferential groove provided a channel for the leakage flow, which could quickly pass through the groove, and reduced the absolute flow angle at the blade inlet nearing the shroud and weakened the trend of the tip leakage flow to upstream. The low-frequency pressure pulsation was eliminated, and the amplitude of the blade passing frequency was reduced under 0.7 Qd (Qd is the design flow rate). The reverse flow thickness coefficient became zero with the circumferential groove. The proportion of the reverse flow volume to the volume of inlet pipe decreased from 14.7 % to 2.2 % under 0.4 Qd. This research indicated that the circumferential groove arranged in the shroud could effectively suppress or eliminate reverse flow.