Part-Load Vortex in the Draft Tubes of Francis Turbines: Numerical Simulation and Investigations

At part-load operation the flow in the draft tube of Francis turbines develops an unsteady rotating flow pattern, the draft- tube vortex, which causes pressure pulsations. Previous CFD studies have shown that a reliable prediction of the complex vortex structure in a draft tube at part-load operation requires highly accurate numerical methods. This paper extends the earlier work with two extensive parallel transient CFD computations on very fine grids, including the interaction between guide vane, runner and draft tube and prediction of the cavitating vortex rope.