Active Control of the Vortex Induced Pressure Fluctuations in a Hydro Turbine Model via Axial and Radial Jets at the Crown Tip

This paper presents an active method to control the pressure fluctuations induced by the rotating vortex rope (RVR) in a Francis hydro turbine model under part load conditions. The control method is based on the injection of axial or radial jets through a stagnant crown attached to the hydro turbine runner. A wide range of injection strategies are compared, and the effectiveness of suppressing pressure fluctuations is analyzed in terms of the spatial distribution of the jets and the flow rate required to suppress the oscillations. The experiments are performed on a fully automated aerodynamic test rig. The pressure fluctuations are quantified using data from the four acoustic sensors placed at a cross section in the cone of the hydro turbine draft tube. The best suppression of pressure fluctuations is achieved with a radial actuator. At a control flow rate of 2% of the main flow, the pressure fluctuations at the vortex rope frequency are reduced by 80% in terms of PSD compared to the baseline case without control. The presented control method will be useful for extending the operating range of Francis hydro turbines.