Development of the Risø wind turbine airfoils

Abstract

This paper presents the wind turbine airfoil development at Risø. The design method is described together with our target characteristics for wind turbine airfoils. The use of the CFD code Ellipsys2D for prediction of final target characteristics is described together with the VELUX wind tunnel testing setup. Three airfoil families were developed; Risø-A1, Risø-P and Risø-B1.The Risø-A1 airfoil family was developed for rotors of 600 kW and larger.Wind tunnel testing and field testing showed that this airfoil family is well suited for stall and active stall control. However, sensitivity to roughness was higher than expected. Field tests of a 600 kW active stall wind turbine showed an estimated reduction in blade fatigue loading of up to 15% at the same annual energy yield and at the same time reduced blade weight and blade solidity. The Risø-P airfoils were developed to replace the Risø-A1 airfoils for use on pitch controlled wind turbines.Improved design objectives should reduce the sensitivity to roughness, but measurements are not yet available.The Risø-B1 airfoil family was developed for variable speed operation with pitch control of large megawatt sized rotors. Wind tunnel testing verified the high maximum lift for these airfoils, and the airfoils were found to be very insensitive to leading edge roughness. Performance with vortex generators and Gurney flaps in combination was found to be attractive for the blade root part. Field testing of a 1·5 MW rotor is in progress.

Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Stable Boundary Layer: Part 2, the Wake Flow

“…Now C L = 0.6 is about half that of a typical wind-turbine blade in low to medium wind speeds (see, for example, Fuglsang and Bak (2004). But, rather conveniently, in blade-element theory both C L and also C D are in product with the blade chord, c. Therefore, in the design of these model turbines the blade chord was enlarged by a factor of 2 from that initially supposed.…”

Wind Turbine Blade Design

“…The sensitivity of blades to soiling, off design conditions including stall and thick cross sections for structural purposes are the main driving forces for the development of wind turbine specific aerofoil profiles [1,26]. The use of modern materials with superior mechanical properties may allow for thinner structural sections with increased lift to drag ratios at root sections.…”

Wind Turbine Blade Design

“…The classification shows the geometric profile of a NACA aerofoil where the 1st digit refers to maximum chamber to chord ratio, 2nd digit is the camber position in tenths of the chord and the 3rd & 4th digits are the maximum thickness to chord ratio in percent [24]. The emergence of wind turbine specific aerofoils such as the Delft University [23], LS, SERI-NREL and FFA [6] and RISO [26] now provide alternatives specifically tailored to the needs of the wind turbine industry.…”