Development of the Riso wind turbine airfoils

This paper presents the wind turbine airfoil development at Riso. 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; Riso-A1, Riso-P and Riso-B1. The Riso-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 some annual energy yield and at the same time reduced blade weight and blade solidity. The Riso-P airfoils were developed to replace the Riso-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 Riso-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 flops in combination was found to be attractive for the blade root part. Field testing of a 1.5 MW rotor is in progress. Copyright (C) 2004 John Wiley Sons, Ltd.