Influence of 3D Guide Vanes on the Channel Vortices in the Runner of a Francis Turbine

It is known that the pressure fluctuation in the runner will become large when a Francis turbine operates at the low flow rate and high head. One of the reasons is the occurrence of channel vortices, which are caused by the three-dimensional flow separating from the suction side of runner blades. In this study, two three-dimensional guide vanes (1# 3D GV, 2# 3D GV) are designed so as to depress the channel vortices and improve the operation performance of a Francis turbine. The flow rate equation for 3D GV is derived firstly in this paper. Then, in order to show the influence of 3D GV on the turbine characteristic, performance test and video-recording of the channel vortices are conducted. Numerical simulation for a part load operation is applied finally to the entire turbine flow passage (from the inlet of spiral case to the outlet of draft tube) using the RNG k-e turbulence model to make clear the three-dimensional internal flow. From evaluation of both the experimental and calculation results, it is noted that the channel vortices from the blade suction side were suppressed effectively by 3D GV, and the turbine efficiency with 3D GV was 0.41 % higher than that with the conventional 2D GV.