A Flow Study in Francis Turbine : Part4, Effect of Number of Blades and Blade Length on Performance

In this paper, the effect of number of blades and blade length on the performance of Francis turbines was experimentally and analytically studied. The model turbine has the specific speed of Ns=240 m-kW. The effect on the performance by changing number of blades and blade length is represented systematically by using the chord-spacing ratio (l/t). From the experimental results, it is suggested that the most suitable value of l/t exists for a given specific speed, and it is shown that the value is about 1.8 for the model turbine in this paper. These results are analytically discussed by using one-dimensional loss analysis method.