CFD Based Flow Analysis Of a Francis Turbine

Abstract

Flow analysis in hydropower plants has long been a rigorous subject of research. The costeffective design of hydro turbine is a challenging task and requires critical analysis of the highly complex flow being turbulent and three dimensional in nature. The flow analysis inside the hydro turbine through experiments is very difficult, time consuming and expensive. Use of Computational Fluid Dynamics (CFD) for the analysis of flow in hydro turbines has increased in recent years due to the development of the high speed computers, evolution of CFD and its easy use. Flow analysis of Francis turbine carried out using commercial CFD package “FLUENT” is presented in this paper. The computational domain consists of spiral casing, 18 numbers of stay vanes and guide vanes, runner having 13 numbers of blades and a draft tube. The steady state simulation has been carried out at design and off-design conditions using Reynolds averaged Navier-Stokes (RANS) equations with three different turbulence models. To consider the rotational effect, moving reference model with grid interface between stationary and rotating components has been used. Based on the analysis, it is found that non-uniformities are created in different components at off-design conditions which result in decrease in efficiency. In the draft tube, regions of secondary flow, low pressure and vortices are observed at different operating conditions. The CFD results are compared with the results of model testing provided by the manufacturer and are found in very good agreement.