EFFECT OF DIFFUSER LENGTH ON PERFORMANCE CHARACTERISTICS OF ELBOW DRAFT TUBE WITH DIVIDING PIER

The hydraulic turbines extract the energy of flowing water and converts into mechanical energy. The reaction turbine has components namely casing, stay ring, guide vane, runner and draft tube. Each component plays some role in performance of turbine. Out of above component casing, stay ring and distributor guide the flow while in runner and draft tube energy transfer and conversion takes place. In reaction turbine, significant part of input energy goes out of runner unutilized in form of kinetic energy. Draft tube are provided at exit of runner to connect turbine and tail race providing closed conduit flow of varying cross sectional area. The development in the design of turbines leads to different shape of draft tube to recover as much energy as possible. The elbow draft tube is mostly used with large reaction turbine. It is found that geometry of draft tube, flow space affects its performance to large extent but due to limitation of experimental investigation, the mesh were limited to few shapes. The growth on computational power has made it possible to investigate the many alternative design of draft tube. In the present paper, numerical simulation has been done for a large elbow draft tube with pier in diffuser. The length of diffuser has been changed to see its effect on the performance i.e. head and efficiency of draft tube.