Numerical simulations of a swirling flow in a francis draft tube

We study the flow in a model Francis-99 draft tube for partial load conditions using Large-eddy simulations. 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 simulations. 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.