Performance prediction of a centrifugal pump as turbine using rotor-volute matching principle

A large number of studies have been reported on the prediction of head and flow rate conversion factors (h and q) at the best efficiency point (BEP) between pump and turbine mode, but the theoretical and experimental correlations are usually valid only within a certain range of specific speeds for pumps. In this paper, an innovative theoretical approach is introduced to predict the flow rate and head at BEP both for pump and turbine mode, according to the principle of characteristic matching between rotor and volute. A theoretical formula of rotor characteristic in turbine mode was derived, based on Euler equation of rotomachinery and velocity relations at the inlet and the outlet of the rotor. The formulas were accordingly obtained for predicting the flow rate and head at BEP in both pump and turbine modes. The proposed method is universally effective and practical, related to the major geometry parameters of rotor and volute without restriction of performance data and statistical/empiric range in pump mode. The proposed method was verified by experimental results of three types of pumps in both pump and turbine modes and yielded more accurate results of h and q comparing to several major predicted methods.