Sensitivity of Wind Turbine Airfoil Sections to Geometry Variations Inherent in Modular Blades

In the ongoing work to increase the efficiency of large-scale, horizontal-axis wind turbines, the modular blade concept has been proposed. The aerodynamic performance of modular blades, whose baseline profile remains unchanged from conventional blades but who are susceptible to a larger degree of variation in both manufacturing tolerances and fabrication materials, is yet unknown. This paper works towards quantifying the aerodynamic effects of variations to a baseline wind turbine section, specifically, examining the effects of offsets in the leading edge of the profile and the use of a tensioned fabric as a flow surface over the aft of the profile. Wind tunnel tests were performed on a modified DU91-W2-250 section with an offset in the leading edge and cavities in the aft that were alternatively fitted with fabric-covered panels and rigid aluminum panels. Measurements included lift, drag, airfoil surface pressures, and surface deflection of the fabric material. Preliminary results show the modifications have a noticeable impact on the aerodynamics of the section, including altered surface pressure distributions and wake characteristics.