Aero-structural investigation of biplane wind turbine blades

As wind turbines grow larger, loads increase dramatically, particularly in the inboard region of the blade. A key problem is to design a strong inboard region that supports these loads without sacrificing too much aerodynamic performance. A new design is proposed: a biplane inboard region that transitions into a joint, which connects to a monoplane outboard region. The objective is to develop biplane inboard configurations that improve the aero-structural performance of blades. To approximately compare a conventional inboard region with a biplane inboard region, cross-sectional properties of a thick monoplane and a biplane were measured. Numerical simulations were used to explicitly compare the aerodynamic performance of a thick monoplane with a biplane. Then, several model beams were designed to be simple approximations of a conventional blade (monoplane beam') and the biplane blade (biplane beam'). Canonical bending loads were applied to each model beam, and their deflections were compared. Numerical simulations show that the lift-to-drag ratio is significantly greater for the biplane than the thick monoplane for 0 degrees<<15.5 degrees. A parametric analysis of biplane beam configurations shows that their tip deflections are smaller than monoplane beams of the same length. These benefits for the inboard region of (i) improved aerodynamics and (ii) improved strength could lead to weight reductions in wind turbine blades. Innovations that create lighter blades can make large blades a reality. These results suggest that the biplane blade is an attractive design for large blades. Copyright (c) 2012 John Wiley & Sons, Ltd.