Investigation on disk friction loss and leakage effect on performance in a Francis model turbine

Abstract

In this article, computational fluid dynamics technique has been applied to examine the disk friction loss and leakage effect on performance of a Francis model turbine, and a model test for obtaining hydraulic efficiency of the turbine was also conducted. The analysis of the results shows that near the optimal operating point, computational fluid dynamics can predict accurately the turbine hydraulic efficiency compared with experimental value, validating the applied computational fluid dynamics method. The disk friction loss of the runner is observed to increase with the increment of unit speed, and the band surface of the runner produces more disk friction losses than the runner crown surface. Furthermore, the disk friction loss from the inner surfaces of the band and crown is basically equivalent to the one from the outer surfaces. Doubling the clearance size reduces the total friction loss but decreases the turbine efficiency as well. It is also observed that the pressure field on the runner blade suction side is more sensitive to the clearance size than on the pressure side. Moreover, the leakage flow from the clearance near the runner band deteriorates the inflow condition for the downstream draft tube and the flow pattern inside resultantly. It is also observed that the phenomenon of rotor-stator interaction has very limited effects on both the disk friction loss and leakage loss.