Numerical Simulation of a Swirling Flow in a Francis Draft Tube

Abstract— We study the flow in a model Francis-99 draft tube for partial load conditions using Large-eddy simulation. The swirl is produced by the runner rotating with a constant angular velocity. Within the validation step, we compare results of eddy-resolving simulations with our Particle image velocimetry (PIV) and pressure measurements for three flow cases with different incoming flow rates. The time-averaged velocity fields agree well in experiments and simulation. To study the dynamical features, we analyze spectral characteristics of the flow featuring a strong coherent component. This vortical structure corresponds to the precessing vortex core (PVC) changing the shape and amplitude with the increase in the bulk velocity.