Numerical simulation of 3D cavitating turbulent flow in Francis turbine

Generally, cavitation occurs very easily when liquid local pressure in the Francis turbine falls below the saturated vapor pressure. It will injure the hydropower plant seriously by some problems, and has become one of the main concerns in the field of hydraulic machinery. In this paper, we present steady simulation on cavitation performed through the whole passage of a prototype Francis turbine with mixture model for multiphase flow, and full cavitation model for cavitation effect, from the commercial code of FLUENT 6.1. The simulation is conducted at several operating conditions, and the internal flow conditions and the critical cavitation number were obtained for each case. The simulation results indicate that the internal flow condition in the flow parts before the runner is not affected by the cavitating flow. The tendency of the cavitating flow in the runner and draft tube agrees well with the turbine empirical results, and the critical cavitation number has been quantitatively predicted.