Aerodynamic performance of biplane wind turbine blades

Phillip Chiu Perry Roth-Johnson Richard Wirz

Recent efforts in wind turbine blade design have focused on improving the aerodynamic performance of the inboard section of wind turbine blades. For structural reasons, this area of the blade typically uses thick airfoils that have poor aerodynamic performance. The "biplane blade" is one of a number of "multi-element" blade designs that seek to improve the aerodynamic performance of the inboard region. Through experiment and computations, we seek to better understand the aerodynamic performance of biplane wind turbine blades.

Compared to traditional monoplane wind turbine blades, relatively little is known about the aerodynamics of biplane turbine blades. We seek to better understand the aerodynamics of biplane airfoils both quantitatively, by evaluating their aerodynamic performance, and qualitatively, by examining the flow phenomena around these blades. This understanding can better guide blade designers who wish to use biplane or other multi-element airfoils.

In our 2D measurements and computations, biplanes with thick airfoils were shown to have improved lift when compared to single lifting bodies. A parametric analysis revealed how the aerodynamic performance was affected by the relative positioning of the two airfoils. Unique stall characteristics were observed - which may lead to reduced dynamic loading on the turbine blades. Going forward, we hope to reveal the mechanisms that lead to this improved aerodynamic performance. Through shape optimization, we will design optimized biplane profiles for various sections along the blade. Finally, using 3D CFD we will quantify the overall performance of rotors using biplane blades.