Numerical and experimental investigation of the runner channel vortex in Francis turbines regarding its dynamic flow characteristics and its influence on pressure oscillations

Abstract

With the increasing demand for more flexibility in the operation of hydraulic machines, the operation range of Francis turbines has been progressively extended towards deep part load, where the channel vortex is present in the runner. Its set-in is often associated with increased pressure oscillation amplitudes in the vaneless space and runner. The runner channel vortex (RCV) is commonly observed during model test at reduced flow conditions. However, there is limited research available on its fluid dynamic fundamentals, on its origin, on its transition from incipient to fully developed vortical structure and on its relation to pressure oscillations.