Numerical Analysis of Cavitation Effects in Low-Head, Medium-Specific Francis Turbines for Small Hydroelectric Power Plants

A numerical analysis study has been carried out in Francis turbine due to cavitation for small hydro power plants using the commercial CFX code. The transient simulation is carried out by considering the turbulence model, namely, Shear Stress Transport (SST) and cavitation mass transfer i.e., Rayleigh-Plesset (R-P). Under the present study, the cavitation impact is defined by the pressure contours, cavitating region, and cavitation rate for selecting the three different cavitation index under four operating plant discharge factors i.e., 0.36, 0.79, 1.0 & 1.36 at a low water temperature of 10 0 C. The study has concluded that the probability of the surface damage impact by vapor bubbles is observed for all four plant operating conditions under three different cavitation index. The low pressure region is found significantly on the suction side in the vicinity of a band of the blades for a high plant discharge factor and low cavitation index which leads to ratifying the severe cavitation impact. At the low cavitation index, the cavity region is predicted to 40.25 % more on runner blades when the plant runs under a high discharge factor (= 1.36) compared to the rated condition (= 1.0). Moreover, the cavitation rate increases linearly with the plant discharge factor and is found to be 279 kg.m 3 /s, 62 kg.m 3 /s, 41 kg.m 3 /s, and 2.1 kg.m 3 /s corresponding to the plant discharge factors of 1.36, 1.0, 0.79 and 0.36, respectively.