Effect of blade curve shape on the hydraulic performance and pressure pulsation of a pump as turbine

Abstract

As an economical and convenient device, a pump as turbine (PAT) is widely preferred in the energy recovery process and micro-hydropower plants. To study the operational stability of a PAT, a forward-curved impeller and a back-curved impeller were designed in this paper. A verified computational fluid dynamics technique is used to compare the two different impellers in terms of the external characteristics, energy loss, and pressure pulsation under the partial load flow rate (0.8 Qr), design condition (1.0 Qr), and overload flow rate (1.2 Qr). The results show that the total entropy generation power of the forward-curved impeller is 41.6%, 49.2%, and 53.6%, respectively, which are lower than that of the back-curved impeller. At the best efficiency point, the head, shaft power, and efficiency of the forward-curved impeller are 9.8%, 18.4%, and 13.1%, respectively, which is obviously better than that of the back-curved impeller. Similarly, the main frequency of the pressure pulsation in volute is the blade-passing frequency, and that of the impeller is the shaft frequency. Compared with the back-curved PAT, the pressure pulsations of the forward-curved PAT are decreased by 92.24%, 73.18%, and 62.22% in volute, impeller, and draft tube, respectively. This paper reveals that the forward-curved impeller not only obviously improves hydraulic performance but also significantly improves pressure pulsations within a PAT.