Development of draft tube in hydro-turbine: a review

The efficiency of a hydraulic reaction turbine is significantly affected by the efficiency of its draft tube. The shape (profile) and velocity distribution at the inlet affect the performance of the draft tube. So far, the design of draft tubes has been improved through experimental observations resulting in ‘rules of thumb’ and empirical formulae. In the last two decades the use of computational fluid dynamics (CFD) for research and designing complex profiles has improved significantly due to its flexibility and cost-effectiveness. A CFD-based design can further be aided with robust and user-friendly optimisation. Numerical analysis of fluid through a draft tube is challenging and time consuming due to complex flow features. Hence there is a need for developing accurate and reliable CFD models together with efficient optimisation. Studies of the principles of draft tube, internal flow pattern, various turbulence models and associated divergence along with results have been presented in this paper. The objective of this paper is to present the application of CFD simulation in design and flow analysis of the draft tube and also find out the factors which influence the deviation of CFD results with experimental results. From the literature, it has been observed that there are several factors (accurate inlet conditions, turbulent models selected for simulation, modification in geometric parameters and accuracy in measurement of experimental results) that influence the draft tube design and performance. Thus, there is a scope of research for optimisation of geometrical parameters of the draft tube for its best performance at full load condition using CFD simulation. It is carried out by applying 3D velocity as an inlet boundary condition measured with particle image velocimetry/laser Doppler velocimetry. © 2015 Informa UK Limited, trading as Taylor & Francis Group.