Design And Performance Assesment Of A Diffuser Augmented Turbine For Power Generation

During recent years, there has been a tremendous development in the field of renewable energy. As the problem of global warming is being intensified with the passage of time more emphasis is being given on the production of electricity by unconventional methods. This not only reduces the green house gases emitted by burning the fossil fuel in traditional power plants but can possibly generate electricity at much cheaper costs.Open turbines extract energy from the fluid by reducing the flow velocity with little or no pressure reduction as the fluid passes through the turbine rotor. The streamlines must therefore expand to maintain continuity and they cannot expand indefinitely:hence there is a theoretical limit to the percentage of kinetic energy that can be extracted from the fluid. This limit has been shown by Betz to be 16/27 or 59.3% for a single actuator disk (i.e. surface across which energy is extracted as the flow passes through it). But if a duct is provided around the turbine, the flow boundaries are defined and streamline expansion is limited by the duct geometry. Energy is extracted primarily by a pressure drop, and in this way the turbine behaves more like an ultra-low head hydro turbine than like a conventional wind turbine. The maximum power available is the product of flow multiplied by the available pressure drop. Radial flow along the blades of an axial flow turbine is prevented by a duct, and high conversion efficiencies are achievable.The pressure drop available to a ducted turbine depends on the shape of the duct and the flow through and around it. If the duct is designed as a diffuser it will draw more fluid through it and will also increase the available pressure drop across the turbine by recovering some of the velocity head downstream as pressure head. The turbine then becomes "diffuser-augmented." Considerable work has been done on diffuser-augmented wind turbine design, but the concept has not so far been systematically applied to water turbines.The objectives and scope of the present research work are: a) To design a diffuser for a 10 kW tidal turbine using CFD software. b) Optimize the diffuser performance. c) Assess the performance of turbine with and without diffuser. d) Suggest further improvement.Our research work emphasize on the diffuser design for an underwater turbine which concluded successfully the diffuser design is capable of increasing the power output to twice of the original turbine without diffuser. The two diffuser design finalized have almost similar performance with one having flange performing a little better but having the disadvantage of having large drag force and vice versa. The practical application can be decided based on the requirement and loading conditions where the turbine has to be installed.