Stereo-PIV study of unsteady flow in a laboratory air hydro turbine model over a wide range of operating regimes

Swirl flow with the formation of a precessing vortex core (PVC) in a hydro turbine draft tube model was studied using Stereo-PIV and four acoustic sensors. Experiments were performed on an aerodynamic setup in a wide range of operating conditions of the hydro turbine. Using a spatial Fourier decomposition of pressure pulsation data obtained from four acoustic sensors, a PVC was observed for part-load operating regimes (0.3-0.7Qc ). Mean flow features were shown for the range of operating regimes from a deep part-load regime (0.3Qc ) to an overload regime (1.5Qc ). Based on phase-averaged velocity distributions, the PVC spatial structure was identified for maximum pressure pulsations on the cone walls of the draft tube.