Design of Spiral Casing of Francis Turbine for Micro Hydro Applications

Abstract

Spiral casing is an important component of Francis turbine for even distribution of kinetic and potential energy of water so as to achieve the required reaction for better performance of the runner. Optimal design and analysis of spiral configuration is challenging, especially when the turbine is operating in a low head range due to the necessity of a large cross-sectional area of the casing to accumulate the large flow. The main objective of this study is to design the best configuration of cross section of spiral casing which have a very minimal pressure loss and can provide required inlet flow condition for stay vanes. For this, spiral casing configurations following free-vortex theory with different cross sections i.e. circular, trapezoidal and square are designed and analysed numerically. Pressure, radial and tangential velocity distributions are compared for different cross section of spiral casing suitable for micro hydro applications. Considering the ease of manufacturing, flexibility of dimension adjustments and comparable performance with that of the circular spiral casing, trapezoidal casing is found to be an appropriate alternative for such applications.