Encasing of wind turbines in ducts to increase wind energy extraction has been under study for several decades. Ducts are meant to accelerate the wind speed past the wind turbine rotor enclosed in the duct. The most common duct used in wind turbines is a diffuser. Wind speed augmentation in diffusers depends on the geometrical shape parameters of the diffuser, mainly the diffuser expansion angle img width="23" height="16" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image001.png" / and the non-dimensional length img border="0" width="28" height="36" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image002.png" /. This paper addresses wind speed augmentation by empty conical diffusers. It presents the dependence of the wind speed augmentation on the diffuser geometrical shape parameters and the optimum geometrical shape parameters for maximum wind speed augmentation. It is shown that for a given img border="0" width="28" height="36" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image002.png" /, wind speed augmentation increases with img width="9" height="16" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image003.png" / up to the maximum wind speed augmentation and starts to decrease. Each img border="0" width="28" height="36" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image002.png" / has a unique img width="9" height="16" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image003.png" / which gives the maximum wind speed augmentation. It has also been shown that the maximum wind speed augmentation increases with img border="0" width="28" height="36" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image002.png" / For img border="0" width="68" height="36" src=" http://article.sciencepublishinggroup.com/journal/299/2990001/image004.png" / wind speed increased from 1.48 m/s to 1.55 m/s.
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