A comprehensive investigation of hydraulic performance and internal flow characteristics of Francis turbine model at part load cavitating flow for various turbulence models

Francis turbines are used extensively in hydropower facilities because of their great efficiency and versatility in a wider range of operations. In high specific speed turbines, part-load (PL) operations and cavitating conditions introduce highly complex internal flow structures that are challenging to predict accurately while keeping computational costs reasonable. This study offers a detailed comparison of various turbulence models under these demanding conditions and highlights the most effective model that successfully captures the flow intricacies with an optimal balance between accuracy and computational efficiency. Using various turbulence models, including scale adaptive simulation-shear stress transport (SAS-SST), SST, standard [Formula: see text], and standard [Formula: see text], this study examines the internal flow characteristics and performance of a Francis turbine with a specific speed of 276 under PL with cavitation inception point. The investigation shows how well the transient nature of flow inside the high-class turbine under cavitation condition is predicted by different turbulence models. Both steady and unsteady numerical simulations were performed, and the results were verified against experimental data. The SAS-SST model performs better than other models in resolving unsteady flow patterns, forecasting transient phenomena, and capturing instabilities caused by cavitation. In the runner domain, the SAS-SST model showed 58.2% lower eddy viscosity ratios and in the draft tube vortex rope volume is estimated 95.3% greater than [Formula: see text]. The [Formula: see text] model was noticeably worse at capturing transient effects than the other models. The most dependable model for comprehending intricate flow dynamics in PL and cavitation-prone environments is the SAS-SST model.