A Numerical Investigation of Inner Flow in a Turbine with Special Emphasis on Its Pressure and Velocity Distributions

A three-dimensional numerical investigation is conducted to clarify the internal pressure and velocity distributions in a hydraulic turbine under multiple operating conditions. The study aims to identify the main high-gradient regions and the influence of operating parameters on the internal flow field. The incompressible single-phase Navier–Stokes equations are solved using the SST k-ω turbulence model. Eleven operating conditions with different guide vane openings, net heads, output powers, and discharges are simulated using a full-passage turbine model with mass flow inlet and static pressure outlet boundary conditions. The numerical results are validated against experimental performance data. The results show that the pressure and velocity fields exhibit generally symmetric distributions in the circumferential and axial directions, whereas strong local gradients appear in the rotor–stator interaction region. Local high-pressure and high-velocity zones are mainly observed near the blade leading edges, while low-pressure and low-velocity regions develop near the trailing edges, runner cone, and draft tube. Increasing the net head raises the overall pressure and velocity levels and enhances the low-pressure and low-velocity regions in the draft tube. Under a fixed head, increasing the guide vane opening mainly affects the flow distribution around the stay and guide vanes and modifies the flow structure in the runner cone and draft tube. These findings provide a systematic numerical characterization of the pressure and velocity distributions in the turbine and help identify critical regions for further hydraulic performance analysis and flow field optimization.