Vortex-Wake-Blade Interaction in a Shrouded Axial Turbine

This paper presents the results of time-resolved flow field measurements of a multistage shrouded axial turbine. The unsteady interaction mechanism between the rotor’s secondary flow vortices, the rotor’s wake and the adjacent blading at the exit plane of the first turbine stage is of prime interest and analysed in detail. Three key phases are identified for one blade passing event. The first phase shows a quasi undisturbed convection of the rotor’s secondary flow field into the downstream stator. The second phase shows a migration of high loss fluid from the wake layer into the passage and horse-shoe vortices at the rotor hub section. The relative motion between the rotor and stator blades brings the two vortices closer to the wake layer and lets the flow features interact with each other. The third phase focuses on the rotor indigenous hub vortices that are bent and stretched around the stator’s leading edge. The signal analysis of the time-resolved flow field indicates a high level of unsteadiness at the stator’s pressure side. The associated unsteadiness within the flow field is evaluated and quantified on the basis of pitchwise averaged space-time diagrams. The obtained results are finally discussed and explained using two flow schematics within and at the end of the paper.