Design of a passive-adaptive slat for a rotor blade of a horizontal-axis wind turbine

Abstract

Due to mainly structural designed profiles and locally high angles of attack, wind turbine blades often operate with flow separation on the roots suction side. Methods to avoid detachment can increase the performance of the wind turbine and improve the blades lifetime by reducing alternating turbulent loads. Hence, several studies for the use of rigid slats to avoid a stalled flow at the blades upper side have been done so far. Because of the resulting gap flow a slat device reduces the profile performance parameters such as the lift to drag ratio compared to the original profile without a slat for small angles of attack. Hence, the slat should be able to open and close with reference to the incoming flow. In order to reduce the complexity of such a slat device Schmidt and Wild (2021) designed a passive-adaptive slat for a section profile of the reference rotor blade in the project SmartBlades 2.0, which moves without the need of an electrical or hydraulical system. The developed slat leads in most conditions to a better aerodynamic performance in comparison to the same airfoil with a rigid slat and in comparison to the original airfoil without a slat device. Hereby, the maximum lift coefficient could be increased by up to 130 % for the airfoil with passive-adaptive slat in comparison to the original DU-91-W2-250 airfoil. Based on the two-dimensional design of the passive-adaptive slat, different three-dimensional slats were designed for the SmartBlades 2.0 reference rotor blade. The aerodynamic coefficients of each airfoil with and without slat were calculated using 2D RANS simulations with the CFD-code DLR-FLOWer and extrapolated for a 360 degree angle of attack range. Based on the calculated aerodynamic coefficients the rotor blade with and without the designed passive-adaptive slats were afterwards investigated with the Blade Element Momentum method by the use of the software Qblade. Hereby, a higher power generation was predicted for every geometry with open slat in comparison to the reference geometry in the low wind speed region. First 3D-CFD results of the rotor blade including the passive-adaptive slat confirm the positive effect of the designed geometry. The flow is mainly attached in the section where the passive-adaptive slat is installed, which stresses the positive effect of the use of such a slat device for a wind turbine rotor blade. The project SmartBlades 2.0 was funded by the German Ministry of Economic Affairs and Energy (BMWi) on decision of the German Parliament (funding reference no. 0324032D).