An in-depth numerical analysis of transient flow field in a Francis turbine during shutdown

Power production from intermittent renewable energy resources, such as solar and wind, has increased in the past few decades, leading researchers engineers to establish techniques preserve a stable electrical grid. Consequently, hydraulic turbines are being used more frequently transient operating modes regulate The present work provides comprehensive numerical study on flow field of high-head Francis turbine model throughout shutdown sequence. computations were performed using OpenFOAM, utilizing SST-SAS turbulence model. A Laplacian smoothing scheme is employed conduct mesh deformation guide vane domain. time-averaged draft tube velocity at steady Best Efficiency Point (BEP) validated against experimental data. Then different aspects sequence carefully assessed explained for first time. Short-Time Fourier Transform (STFT) analysis carried out fluctuating part static pressure force signals. High-amplitude low-frequency oscillations, due formation Rotating Vortex Rope (RVR) observed during specific period Thereafter, deep load conditions, RVR vanishes and, wide range stochastic frequencies identified minimum load. signal coherence was accomplished distinguish deterministic frequencies. variation described detail with help triangles. An in-depth explanation vortical structures whole presented. physical mechanism destruction thoroughly explained. • Numerical simulation OpenFOAM. High fluctuations RSI resolved. broad condition. Strong stagnant region swirling develops tube. Formation collapse structures, RVR, detail.