A study on the use of existing pump as turbine

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 turbine using existing pump and a comparative study of the cavitation characteristics on a centrifugal pump as turbine 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 the trailing edge on the impeller blades. Also, in the pump, the cavitation became larger from shroud 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 drawn up at the runner outlet near trailing edge on the blade suction side.