Vortical structures in the cavitating flow in the Francis-99 draft tube cone under off-design conditions with the new omega vortex identification method

Abstract

The Francis turbine that operates at an off-design load exhibits a strong twist flow near the runner outlet, which causes a cavitating vortex rope on the draft tube cone. The purpose of this study is to apply the new omega vortex identification method (Ω method) and analyze and compare it with traditional methods in regard to its ability to capture the vortex rope in a Francis-99 draft tube cone under an off-design load. The advances of the Ω method for vortex identification on the cavitating flow are elaborated and analyzed. The significance of parameter ϵ in the Ω method is also highlighted. The determination of ϵ is further examined and adjusted in this study. Finally, this study demonstrates that the Ω method can be successfully applied to capture vortex structures in the cavitating flow of Francis turbines.