Flow characteristics and influence associated with inter-blade cavitation vortices at deep part load operations of a Francis turbine

At a deep part load operation, Francis turbines are subject to the formation of inter-blade cavitation vortices inside blade channels, however its characteristics are not fully understood yet. The present study aims to investigate the development of the inter-blade vortex as well as the flow characteristics associated with the vortex formation inside the blade channel, by using the unsteady RANS simulation. The velocity survey reveals the appearance of the back flow region in the vicinity of the hub near the trailing edge, which seems closely linked with the inter-blade vortex development. Furthermore, the local influence of the inter-blade vortex is evaluated by the specific energy loss calculated from the rothalpy in the blade channel. The comparison of the different operating conditions evidences the impact of the inter-blade vortex presence on the energy dissipation through the blade channel.