Multi-Element Airfoil Configurations for Wind Turbines

Abstract

The extremely thick blade root airfoils of the modern megawatt-scale wind turbines are prone to having sharp stall characteristics with associated unsteady aerodynamic blade loading and fatigue. With current technology designs reaching 45% thickness, these thick airfoils are incapable of producing high lift, and as a consequence they are aerodynamically and structurally sub-optimal. A computational study investigated candidate multi-element airfoil configurations that would serve as an aerodynamic fairing for an assumed spar cap geometry based on the DU 00-W-401 blade root airfoil geometry. Seven multi-element airfoil configurations with varying combinations of flaps, slats, and struts were developed and refined using an inviscid multipoint inverse airfoil design method. The airfoil configurations were then analyzed at Reynolds numbers typical of a utility-scale wind turbine. All of these configurations demonstrated the capability to produce significantly higher lift-to-drag ratios and lift coefficients than the baseline DU 00-W-401 airfoil, with Cl=Cd max increases of up to 82%. In addition to this performance increase, some of the configurations demonstrated a significantly gentler fall off in Cl=Cd at angles of attack greater than a Cl=Cd max . In addition to the higher lift-to-drag ratios and lift coefficients, these multi-element configurations are expected to offer better start-up performance due to higher start-up torque and also higher blade efficiency from more closely matched ideal operating conditions.