Studies of the Effect of Vortex-Control Grooves on Pressure Oscillations in a Francis Turbine Draft Tube

In case of the hydro turbine operated deviated from the designed condition, vortex ropes usually occur in the draft tube, and consequently generate large pressure oscillations. This kind of unsteady flow phenomenon is believed to be harmful for hydropower stations. In this paper, the authors designed a runner with vortex-control grooves and numerically simulate the flow in a Francis hydro turbine using the SAS-SST turbulence model. The pressure oscillations induced by the vortex rope under several operation conditions were analyzed based on the calculation results. It is indicated that the runner with vortex-control grooves can alleviate the pressure fluctuation at part load conditions. However, vortex-control grooves may enhance the swirling flow, and cause a small hydraulic performance drop at full load conditions. Thus, the design optimization of vortex-control grooves is necessary and will be conducted in the future.