Experimental analysis of the operation of a small Francis turbine equipped with an innovative aeration device

Development of hydropower as renewable energy source is an actual trend within the worldwide energy strategy. Thus, the manufacturers and operators of hydraulic turbines are currently engaged in their ecological use. Some of the solutions tested for the development of environmentally-friendly turbines are the aeration devices. Their aim is to increase the dissolved oxygen level in the flow discharged from the turbines in order to improve the quality of the aquatic life downstream hydropower plants. The present paper presents the experimental analysis of an innovative air injection device influence over the main operation parameters of a small Francis hydraulic turbine. The aeration device is mounted downstream turbine runner, at the entrance of the turbine draft tube. The tests are focused on determining the operating parameters evolution of the turbine - generator assembly and the vibrations in the shaft bearings and in the casing of the unit during normal regime and with different injected air flow rates. The pressure in the elbow of the draft tube is recorded, in order to determine the influence of the air injection over the flow at the runner outlet. Six operating regimes of the turbine are analysed, between a minimum power output value and a maximum value. For each operating point various air flow rates are injected in hydraulic system, between 1% and 8% water flowrate. The results will present the influence of the air injection over the dynamic behaviour of the turbine-generator unit.