An Assessment of the Loss Distribution in Francis Turbines

Scalable loss in Francis model turbine is analyzed for four runners with various number of blades which are tested in the same model turbine. The flow in the stay vane, the guide vane and the runners are analyzed by a 3D Euler flow analysis code, and then three methods of boundary layer calculations are carried out in order to obtain scalable loss. As for spiral casing and draft tube, scalable loss is obtained by the analogy of pipe flow. Prom the comparison between runners, the difference in peak efficiency seems to be mainly caused by non-scalable losses. Therefore scalable loss itself is most suitable to be prescribed in the scale-up formula than loss distribution coefficient. Problems on the effect of number of blades might be solved by using scalable loss in scale-up formulae