Investigation on Design Parameters of a Francis Turbine Runner for Optimization Based on 3-D Inverse Design Method

In this paper, an effect of a blade loading and a lean angle at a runner inlet are investigated to understand the internal flow and the loss in the turbine runner. Furthermore, a new Francis turbine runner is designed to improve the turbine performance by the optimization method using the 3D Inverse Design Method and Computational Fluid Dynamics (CFD). According to the investigation of the blade loading and the internal flow, the pressure gradient and the centrifugal forces cause the spanwise secondary flow on the meridional plane of the runner. Also, it is confirmed that designing a runner with the after-loading at every span on the blade is effective in reducing the pressure gradient near the runner inlet, minimizing the spanwise secondary flow, and improving the performance. For the lean angle at the runner inlet, the positive blade lean angle, i.e., the band side forward inclination in the direction of runner rotation, is effective in reducing the pressure gradient on the meridional plane and controlling the secondary flow. The performance of the new runner optimized based on the discussion above has demonstrated the effectiveness of this investigation. These findings and the optimization method will be of great use for designers to develop or improve the turbine performance.