Design of a 2-D Fairing for a Wind Turbine Tower

摘要

An aerodynamic shroud was designed to reduce the effects of the wind turbine tower wake on the blades of a downwind rotor. For a given tower diameter and wind speed the shroud was designed to have the minimum drag and minimum chord length downstream of tower centerline, while being able to self-align and resist flow separation when subjected to a non-zero angle of attack. The initial analysis was run using XFOIL and showed that a three-to-one chord-to-thickness ratio resulted in the minimum drag. Based on this result, the NACA0033 airfoil was selected as the baseline. Further analysis showed that a shroud of this shape will not self-align due to the tower center being located behind the aerodynamic center. A new series of airfoils was created to have a 33% thickness ratio starting from a NACA0028, NACA0030, and NACA0031. The resulting airfoils all had significant adverse pressure gradients near their maximum thickness locations that could lead to flow separation. A new group of airfoils were created by adjusting the existing airfoil geometry using PROFOIL. Of the 13 airfoil designs that were analyzed, the C30u design had the best overall performance and met all of the objectives. At a Reynolds number based on tower diameter of 8.3×10~6, the C30u design had a drag coefficient based on inscribed tower diameter of 0.0193, which represents a 97.5% reduction in the drag of the cylinder. At a 5 degree angle of attack, the C30u design had a pitching moment coefficient of-0.0128.