Experimental rotordynamics and flow visualization approach for periodically reversed flows of a Francis - Type Pump - Turbine in generating mode at off - design operating conditions

Abstract

A non-conventional tufting visualization method along with an image processing development and specific applied technique adapted to the flow conditions is proposed and implemented on a reduced scale model of a Francis-type reversible pump-turbine in three different turbine stages such as turbine mode, runaway mode and turbine break mode, in order to visualize rotating stall phenomenon -- Fluorescent monofilament wires along with high speed image processing and pressure sensors were installed in the narrow and vane less gap between the impeller blades and guide vanes -- Pressure fluctuations were analyzed along with tuft visualization to describe the flow with and without rotating stal