Draft tube guide vane system to mitigate pressure pulsations

Abstract

The present study introduces the concept of mitigating pressure pulsations in a hydro-turbine draft tube. The concept refers to using an adjustable guide vane system in the draft tube. The adjustability relates to its ability to rotate around an axis. The test rig for the experimental study is a high-head Francis model turbine. Three sets of guide vanes are distributed evenly circumferentially in the draft tube. Each guide vanes consists of two hydrofoils. The upper hydrofoil can move around an axis. The lower hydrofoil is fixed. The turbine operating head for the experiments was 12 m. The operating condition considered is at part load, for Q/Q BEP = 0.71. The results indicate that using the guide vanes in the draft tube, the plunging mode of the rotating vortex rope becomes insignificant for nearly all upper hydrofoil configurations considered. The reduction in the rotating mode of the vortex rope is between 50% and 80%. The vortex rope frequency shifts from 0.307·f 0 and varies between 0.33·f 0 to 0.617·f 0 , which is a function of upper hydrofoil angles