Numerical study on flow characteristics of shroud with and without flap for wind turbine applications

Abstract

Shrouded wind turbines have the shroud added to the rotor’s circumference, enhancing wind power compared to conventional wind turbines. This article aims to design a shorter aerofoil cross-sectional enclosure for the wind turbine that improves average velocity and reduces drag, duct material volume, and tower load. Numerical simulations were performed to understand the characteristics of shroud alone and shroud with flap using ANSYS Fluent in the operating regime of the small wind turbine. The influence of the shroud’s length-to-diameter L/D ratio and angle on the performance was analyzed using a one-factor-at-a-time (OFAT) approach, and the optimum values were found. Then the analysis was performed by including the flap at the exit of an optimized shroud. The shroud with flap results showed enhanced average velocity, increased mass flow rate, and higher drag forces than a single long shroud. In order to reduce the drag coefficient, the enclosure geometrical parameters were analyzed using the Design of Experiments (DOE) approach. The results show that the shroud L/D ratio significantly affects the average velocity. Moreover, the optimum combination was found as shroud L/D ratio=0.4, shroud angle=9°, flap L/D ratio=0.2, flap angle=16°, and radial distance of 0.2R. The proposed combination helps to get an acceleration factor of 1.78, a drag coefficient of 1.84, and a material volume of 0.7×10−3 m3. It was found that the optimal ratio of shroud L/D could be between 0.3 and 0.6, resulting in a higher acceleration factor, lower material volume, and shorter length. The drag forces acting in the shroud alone and shroud with flap were studied by analyzing the forces in every section. The results show that the negative drag force acts in the shroud’s inner leading edge.