الفهرس 
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Abstract
The present study considers a new wind power technology called ”DAWT” diffuser augmented wind turbine equipped with a brim “wind-lens” in order to investigate the aerodynamic performance characterized by this technology. To achieve this objective, many models of DAWT with different shroud dimensions is numerically investigated using ANSYS CFD software’s.
Four types of compact-style DAWT are investigated experimentally, with different diffuser sectional shapes, length ratios Lt/D and area ratios AR (exit area / throat area).
The results showed that the diffuser type of a cycloid curve for its sectional shape and with (Lt/D =0.221 and AR =1.294) is the most promising shroud shape. It has been chosen in this thesis to investigate the effect of varying the radial tip clearance and the diffuser length on the aerodynamic performance of it.
Three-dimensional transient Numerical Simulations are developed using the commercial CFD software ANSYS FLUENT, by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. Since this type of wind turbines consists of not only rotating blades but also a diffuser shroud with a brim located at the exit section of the diffuser, the flow field around the turbine is highly complex and unsteady.
The results in the present work of diffuser type of a cycloid curve for sectional shape (with length to diameter ratio Lt/D=0.221 and area ratio AR=1.294) showed a good performance characteristic with Cp equal to 0.92 at design tip-speed ratio (λ=4.3). The results also concluded that the diffuser with a tip clearance of 10 mm increases the output power coefficient by a factor of 2.25 compared with an un-shrouded one for the same wind speed and the same turbine characteristics. Increasing or decreasing the tip clearance away from 10 mm is not recommended as it showed an obvious decrease in the power coefficient Cp due to the wake vortex generated around the turbine.