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

TL;DR

This study addresses vortex transport and blade interactions in a reversible pump-turbine under speed-no-load by performing large-eddy simulations on a high-fidelity 120-million-node model. It employs a progression of turbulence models (SAS-SST, DES, and LES with WALE) to resolve unsteady vortical structures and rotor-stator interactions in both turbine and pump modes, validated against experimental torque and efficiency data. Key findings reveal a dominant leading-edge longitudinal vortex that traverses the blade passage and evolves into a 'string of swirls', along with significant draft-tube secondary flows and reversible core flow, signaling potential fatigue mechanisms. The results provide mechanistic insight into vortex-induced loading under extreme operating conditions and can inform design and operational strategies to mitigate blade fatigue in flexible hydropower systems.

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.

Figures (17)

• Figure 1: Computational model of the investigated pump-turbine. The flow directions (P) and (T) indicate the pump and turbine mode, respectively.
• Figure 2: Static pressure and velocity (radial and tangential) variation at the runner inlet vaneless space. x-axis represents the 0 – 360 degrees of the runner circumference along the line $c_1$. Negative radial velocity indicates the vector towards the turbine axis. Negative tangential velocity indicates the vector towards the rotation speed direction of the runner.
• Figure 3: Visual representation and locations of observation points in the guide vane $(\Phi)$, runner $(\Pi)$ and draft tube $(\Psi)$.
• Figure 4: Unsteady pressure fluctuations in the guide vane passage. Scale on y-axis is adjusted for clear visualization of the fluctuations. Pitch $(s)$ on x-axis indicates the time-dependent runner rotation from 0° to 180°.
• Figure 5: Unsteady pressure fluctuations in the runner blade passage. Scale on y-axis is adjusted for clear visualization of the fluctuations. Pitch $(s)$ on x-axis indicates the time-dependent runner rotation from 0° to 108°.