arXiv subjects

Chirag Trivedi

Publications and source records attributed to Chirag Trivedi.

3 recordsLinked to original sources

arXiv2026

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

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.

physics.flu-dyn↗

arXiv2026

Investigation of Wake Dynamics of a Slender Symmetric Trailing Edge Hydrofoil

Accurate prediction of wake dynamics behind hydrofoils is critical for mitigating vortex-induced vibrations and improving the performance of hydraulic machinery. Conventional turbulence modeling approaches often struggle to capture the unsteady, coherent structures governing wake behavior, particularly for slender hydrofoils operating at high Reynolds numbers. This study addresses this limitation by combining scale-resolving numerical simulations, including high-resolution Large Eddy Simulation (LES), with Particle Image Velocimetry (PIV) measurements to investigate the turbulent wake of a symmetric, blunt trailing-edge hydrofoil operating at zero angle of attack. The flow was analyzed at a Reynolds number of approximately 7.5x10e5, i.e. close to the onset of wake-structure interaction effects. LES was performed using a fine mesh of approximately 500 million nodes to resolve near-wall and wake dynamics beyond the experimental field of view, while PIV measurements provided time-resolved velocity fields downstream of the trailing edge. Proper Orthogonal Decomposition (POD) was applied to the PIV data to extract dominant coherent structures and quantify their contribution to the turbulent kinetic energy. POD analysis reveals that energy is distributed across many modes, with the leading mode capturing the primary wake dynamics and higher modes forming coupled oscillatory pairs associated with von Karman vortex shedding. PIV-LES agreement shows that central wake measurements combined with numerical simulations enables full wake reconstruction and validates modeling for vibration-relevant hydrofoil dynamics.

physics.flu-dyn↗

arXiv2026

Numerical investigation of unsteady flow in a reversible pump-turbine

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.

physics.flu-dyn↗