ANALYSES OF MINIMUM SUBMERGENCE AND AIR DISCHARGE IN VERTICAL SHAFTS WITH DIFFERENT INLETS

Intakes and dropshafts conduct water from the inlet towards a vertical shaft connecting to a tunnel, which has the function of discharging to a hydroelectric power plant, irrigation or water supply system. A problem to the hydraulic engineer is to design an intake taking into account the prevention of vortex formation. Vortex with air entrainment can carry away less efficiency of hydraulic machines, reduction of discharge coefficients and vibration. Critical submergence is one of the factors that most influences vortex formation. This study has the objective of investigating minimum submergence conditions in vertical intakes and air entrainment. An experimental study has been conducted through different vertical intake diameters, varying the intake height, submergence and flow. Vortices were classified from low intensity ones with superficial swirl and no depression, to strong ones with air entrainment. The study also compares different inlet types and flow condition, showing that the air entrainment depends on the geometry inlet, being great for radial ones. Results showed that in order to avoid vortices with air entrainment the minimum necessary rate of submergence to intake diameter should be 0,7. It was determined the discharge coefficient for vertical intakes with and without vortex formation and also an evaluation of air entrainment was done.