A study on the use of existing pump as turbine

Abstract

Cavitation is an abnormal physical phenomenon which occurs in relatively low-pressure regions in turbomachinery such as pumps and hydraulic turbines. A comparison between the pump and turbine cavitation behavior is a significant and essential process. The work investigates feasibility of turbineusing existing pump and a comparative study of the cavitation characteristics on a centrifugal pump asturbine numerically and experimentally. The current work adopted the Rayleigh-Plesset cavitation model as the source term for inter-phase mass transfer to predict cavitation characteristics.The experimental data were compared with the numerical results and were found to be in good agreement.Results of the comparative study showed that cavitation first occurred at the suction leading edge on the impeller blades and attached cavitation observed on the impeller blade at the lower suction head in pump mode; however, for the turbine mode, the development of vortex cavitation happened at the runner outlet near thetrailing edge on the impeller blades. Also, in the pump, the cavitation became largerfromshroud to the hub and the cavitation rapidly extended from the suction side to the pressure side. On the other hand in the turbine mode, as the cavitation number decreased more vapor bubbles are drawnup at the runner outlet near trailing edge on the blade suction side.