Improvement of the Runner Design of Francis Turbine using Computational Fluid Dynamics

Abstract

Problem statement: The objective of this study is to improve runner design of the Francis turbine and analyze its performance with the Computational Fluid Dynamics (CFD) technique. Approach: A runner design process uses a direct method with the following design conditions: flow rate of 3.12m³/sec head of 46.4 m and speed of 750 rpm or dimensionless specific speed of 0.472. Results: The first stage involves the calculation of various dimensions such as the blade inlet and exit angle at hub and the mean and shroud positions to depict the meridional plane. The second stage deals with the CFD simulation. Various results were calculated and analyzed for factors affecting runner’s performance. Results indicated that the head rise of the runner at the design point was approximately 39 m, which is lower than the specified head. Based on past experiences, the meridional plane was modified and blade inlet and lean angles were corrected. The process of meridional plane modification was repeated until the head rise was nearly equal to the specified head. Velocity vector and streamline should be a uniform stream. Conclusion/Recommendations: Results from calculating runner’s performance were approximately 90% at design point. Existing absolute velocity component from CFD simulation pointed out that swirling flow occurred at the exit of runner. Based on the comparison of runner’s performance between simulation results and experimental data from previous work reported in the literature, it is possible to use this method to simulate runner’s performance of the Francis turbine.