[Paper Review] Numerical investigation of unsteady flow in a reversible pump-turbine

Chirag Trivedi|arXiv (Cornell University)|Jan 23, 2026

Cavitation Phenomena in Pumps0 citations

TL;DR

This study builds a high-fidelity CFD model of a model pump-turbine to explore unsteady flow in both turbine and pump modes, revealing complex frequency content and Dean vortex effects. It reports validation errors and key flow phenomena, including potential resonance risk.

ABSTRACT

Hydropower is an important source of renewable energy that provides clean energy. Pump-turbine type hydraulic turbine is widely used to mitigate the intermittent energy demand and store a large-scale energy. Pump-turbine operates in reverse mode in pump mode to store energy. Flow conditions in turbine mode and pump mode operations is substantially different. This study investigates the unsteady flow field in the model pump-turbine. A computational model of the pump-turbine was created, and the model included hexahedral mesh of 58.19 million nodes. Total verification and validation error was 7.7%. Three operating conditions in turbine mode and four in pump mode were simulated. Flow characteristics, such as blade loading, time-dependent pressure fluctuations, frequency spectra, radial and tangential velocity were investigated. The frequency spectra revealed amplitude of frequencies up to tenth harmonics of the blade passing frequency in pump mode. The higher harmonic frequencies can potentially reach the high mode eigen frequencies and increase the risk of resonance. Flow field analysis in the draft tube indicted the strong presence of Dean vortices causing highly asymmetric flow at the runner inlet in pump mode operation. This study provides essential insights into the complex flow phenomena and advances the understanding of unsteady flow behaviour in pump-turbines.

Motivation & Objective

• Motivate the study by addressing the need to understand unsteady flow in pump-turbine devices used for energy storage and load balancing.
• Develop a computational model of a reversible pump-turbine with detailed mesh to capture unsteady flow phenomena.
• Characterize flow features such as blade loading, pressure fluctuations, and velocity fields in both turbine and pump operating modes.

Proposed method

• Create a CFD model of a pump-turbine with a hexagonal mesh consisting of 58.19 million nodes.
• Simulate three turbine-mode and four pump-mode operating conditions to study unsteady flow.
• Analyze time-dependent pressure, blade loading, velocity fields, and frequency spectra to identify harmonic content up to high-order blade-passing frequencies.
• Assess model accuracy with verification and validation, reporting a total error of 7.7%.
• Identify flow phenomena such as Dean vortices in the draft tube affecting inlet flow symmetry.

Experimental results

Research questions

• RQ1 What unsteady flow features arise in turbine and pump modes of a reversible pump-turbine?
• RQ2 How do pressure fluctuations and velocity fields evolve in time under selected operating conditions?
• RQ3 What is the spectral content of flow fluctuations and can high-order harmonics approach resonant modes?
• RQ4 What flow structures, such as Dean vortices, influence flow symmetry at the runner inlet?

Key findings

• Frequencies in the spectra include amplitudes up to the tenth harmonic of blade-passing frequency in pump mode.
• High-order harmonics may reach eigenfrequencies of high modes, indicating potential resonance risk.
• Dean vortices are strongly present in the draft tube, causing highly asymmetric flow at the runner inlet during pump-mode operation.
• The computational model achieves a total verification/validation error of 7.7%.
• Flow characteristics such as blade loading, time-dependent pressure fluctuations, and radial/tangential velocities were analyzed under multiple operating conditions.