Two Phase PIV Measurements at the Runner Outlet in a Francis Turbine

Part load operation of hydro turbines with fixed pitch blades causes complex instable cavitation flow in the diffuser cone. Application of PIV systems provides the opportunity to investigate the flow velocity and turbulent fields in the case of development of cavitation vortex, the so-called turbine rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows to apply phase averaging techniques in order to extract both the periodic velocity components and the rope layout. The influence of the turbine setting level on the volume of the cavity rope and its center is investigated, providing a physical insight on the hydrodynamic complex phenomena involved in the development of the cavitation rope at Francis turbine operating regimes.