On the vortex transport and blade interactions in a reversible pump-turbine

TL;DR

This study uses large eddy simulations to analyze unsteady vortex flows and blade interactions in reversible pump-turbines under speed-no-load conditions, revealing flow instabilities that could cause blade fatigue.

Contribution

It provides detailed insights into vortex transport and blade interactions during extreme operating conditions in reversible pump-turbines, a previously underexplored area.

Findings

Identification of a large longitudinal vortex on the blade's high-pressure side.

Discovery of a 'string of swirls' in the draft tube during reversible flow.

Flow instability potential to induce blade fatigue.

Abstract

Pumped storage type hydropower plants play an important role in mitigating real-time energy flexibility. Reversible pump-turbines undergo extreme operating conditions such as runaway and speed-no-load. Very limited studies are undertaken to understand the stochastic flow under these conditions in the reversible pump-turbine. The present study investigates the unsteady vortical flow, its transportation, and interaction with the blades at speed-no-load. Large eddy simulations are conducted in both turbine and pump modes. The computational domain contains 120 million nodes. Numerical results provided evidence of a large longitudinal vortex that develops on the high-pressure side of the blade, and transports into the blade passage and develops the unsteady "string of swirls". The results also showed another "string of swirls" in the draft tube, where flow in the center is reversible (pumping). The resulting flow instability is very high, and it has the potential to induce fatigue damage to the blades.