Investigation on formation mechanism of cavitation channel vortex in the runner of Francis turbine

Abstract

Abstract Cavitation channel vortices generally cause flow state more complex in the runner, leading to the work efficiency is reduced and the cavitation erosion on flow components is enhanced. In this paper, simulation of cavitation flow is carried out for a Francis turbine model, and the evolution of vortices in the runner during cavitation development is analyzed under partial load conditions. The results show that cavitation has a great influence on the morphology and distribution of attached vortices between blades, trailing vortices at the outlet edge of the blades, and vortex near the cone in the runner. With the gradual development of cavitation, the invasion effect of vortex rope in draft tube on the runner is enhanced, and the vortex near runner cone is gradually connected as a whole. Under the effect of the downstream reverse pressure gradient in local low-pressure area, the flow separation area gradually expands to the blade and upstream, and more singular points evolve on flow separation lines, which leads to more trailing vortices at the outlet of the blade and cavitation channel vortices are formed in serious cavitation stage.