Analysis of Inner Flow Inside Francis Turbine Runner Based on Dissipation Function

Energy loss inside a Francis turbine runner is analyzed with dissipation function in this paper. The dissipation rate of a Newtonian flow with constant shear viscous has three constituents from dilation, vorticity, and surface strain, which is derived from kinetic energy equation presented in this paper. A commercial N-S equation solver has been employed for 3D turbulent flow simulation with a model Francis turbine, and three different operating conditions are chosen for comparison, which are part load, rated load, and excessive load. The results from simulation have been compared with model experiments to validate their preciseness and reliability. The distribution of dissipation constituents on runner blade surface have been extracted from the above simulation results. The distinction of these constituents can be used to identify flow structures inside runner. The flow energy loss is determined by dissipation function, thus it can affect the hydraulic efficiency of turbine runner. From the above results, it can be seen that what causes the energy loss, which is the dominant factor, and where it has the highest value. Thus this analysis based on dissipation function can be used for flow diagnosis inside the blade channel, and tell us which part of the blade should be improved to reduce the energy loss.