A Simplified Francis Turbine for Micro Hydro Application: Design and Numerical Analysis

Abstract

Francis turbine is the most widely used type of hydro turbine due to its high efficiency and a wide range of operation. Despite its popularity in large scale power plants, the use of these turbines has not been yet realized for micro hydro applications. Considering the sustainability of micro-hydro power plants, the components of Francis turbine need some simplifications so that the manufacturing and operation of the turbine become more feasible. This study focuses on redesigning the turbine with simplifications in spiral casing and distributor along with investigating its effects on the performance of runner using CFD. Bovet method is used to obtain meridional dimension of runner while Bladegen feature of ANSYS 15.0 is applied to obtain the runner domain. Optimum design of the runner is obtained by analyzing the effect of parameters like wrap angle, lean angle, blade’s beta angle distribution and energy distribution on the runner’s performance. The velocity at the runner inlet is very low for micro Francis turbine which increases the dimension of spiral casing so dimension of spiral casing is made small by adjusting guide vane and stay vanes. A comparative study of conventional and simplified design is made based on pressure and tangential velocity distributions along spiral casing and distributor as well as on the performance of turbine. It is observed that the required reaction ratio and flow conditions can be obtained by combining the stay vanes and guide vanes. In addition, the proportion of combination depends on the magnitude of reaction ratio. It is found that the combining the stay vane and guide vane gives better result in best efficiency point however at other loading condition efficiency is lower which is due to improper stagnation.