Experimental and Computational Comparison Between Widnall and E423 Shroud Designs for an Axial Wind Turbine

For at least 3000 years before using wind to generate electricity, wind power had been used on land, mainly for grinding grain or pumping water, and at sea, as power for sailing ships. In relatively recent times, the usage of wind turbines to generate electricity has gained momentum. This is partially due to environmental threats from fossil fuel usage. It has become essential to look for energy sources which are renewable and clean to eliminate or reduce the environmental pollution and lower economic costs. However, using wind turbines in traditionally low wind speed areas has proved to be economically prohibitive. To address this issue, ducted or shrouded wind turbines have been studied and developed throughout the twentieth century. When the shroud is designed optimally, a lift force is generated by the flow through the shroud, and the effect of this lift is to increase the mass flow rate through the rotor plane. This study compared two shroud designs; the established Widnall design and a new design shaped by revolving airfoil E423 (high lift force) about a center-line. Numerical and experimental simulations were conducted at lower wind speeds in order to compare the augmentation velocity factors of each design. The effect of various design parameters on the shroud performance, namely drag force, area ratio, angle of attack for the shrouds, cost effect, and shroud geometric influences were considered. The computational fluid dynamic techniques were conducted using commercially available software. Experimental investigations on a micro-shroud included measurement of the velocity distribution inside the shroud and determination of the extracted power in these shrouds by placing a small turbine at the throat region. A low speed wind tunnel was used for the experiments. Both of the shrouds (Widnall and E423) were modeled using readily available databases for each airfoil. The models were then manufactured with a 3D printer using PLA plastic material. Results obtained from numerical simulations showed that the velocity factor increased linearly with increasing area ratio and shroud length for both shrouds. Experimental investigations on an empty micro-shroud showed good agreement with the computational fluid dynamics velocity distribution and augmentation velocity factor at the throat area. Power output from the micro-turbine was experimentally determined for a no shroud system, a Widnall shroud system, and an E423 shroud system. Both shroud systems improved the micro-turbine performance. In all instances investigated, the E423 shroud outperformed the Widnall shroud.