Design and Use of Roughness-Tolerant Low Drag Airfoils for Wind Turbine and Hydrokinetic Turbine Applications

Wind turbines and hydrokinetic turbines are designed to use laminar airfoils that provide maximum power at the rated speed. During day-to-day operations, the blade surface may be degraded due to accumulation of dirt and icing on the pressure side, in addition to development of scratches or other surface imperfections. As a result, the profile power losses would increase, reducing the available power over a broad range of operating conditions. In this work, an inverse design approach has been employed to generate roughness tolerant airfoils that exhibit a laminar drag bucket for a broad range of lift coefficients. Two-dimensional drag polars are presented for smooth and rough airfoils and compared to NACA airfoils of comparable thickness. A limited number of three-dimensional studies based on combined blade element-momentum theory are also presented for several wind and tidal turbines for a broad range of rated power conditions.