Cavitating Turbulent Flow Study for Low Head Francis Turbine by Transient Analysis

Abstract

Cavitation is undesirable phenomenon and it is difficult to eliminate completely, however it is minimized to the acceptable limits. It becomes more severe under off-design conditions and lower tail race level. Shear Stress Transport (SST) turbulence model and Rayleigh-Plesset mass transfer models are used using CFX solver for performing the transient simulation and investigating the cavitation turbulent flow through Francis turbine. An attempt has been carried out to analysis of cavitating flow at low head Francis turbine under different operating conditions having varying suction heads. Experimentation has been carried out to validate the simulation results. It was found that obtained simulation results are very close agreement with experimental results. Summarizing, the performance loss and cavitation rate are found maximum under over load operating conditions. At part load operating conditions of the turbine, high amplitude of pressure at low frequency has been found which may cause fatigue damage to the turbine over time. Cavitation rate, performance loss and magnitude of pressure pulsation increase with increase of suction head.