Numerical Simulation of Elbow Draft Tube at Unsteady Flow Condition

The draft tube is one of the important components of Hydraulic reaction turbine and it connects the runner exit to the tail race. The main functions of draft tube is to allow the installation of turbine above the tail race level without loss of head and to convert major part of kinetic energy at the runner outlet into pressure energy .With the use of very low head and high speed turbines the kinetic energy leaving the runner became higher and the height of the runner above the tail race became smaller. This is achieved by increasing the cross-sectional area of the draft tube in the flow direction. Initially the straight conical tubes with inlet and outlet areas of different cross-section were used and part of kinetic energy could be converted into potential energy for use in the turbine.