Drag reducing method for multi-megawatt wind turbine blade

The knowledge of the impact of amplitude modulation of small scales by large-scale motion in a turbulent boundary layer across a wide range of Reynolds numbers has recently been applied to develop a new passive flow separation control method at a high Reynolds number (Rec>10 million) suitable for the longest offshore wind turbine blades.

Preventing flow separation increases the lift force generated by the blade, thus enhancing the efficiency of the power produced by the turbine.

The method utilises a stationary streamwise wavy wall. Ongoing research aims to apply this method to curved surfaces. The local skin friction coefficient behind the wavy wall on suction side of the blade increased by 42%, potentially delaying flow separation under on-design conditions. The technology aims to improve the aerodynamics of offshore wind turbines by using a wavy wall in the streamwise direction to prevent turbulent flow separation on the suction side of large wind turbine blades. Experimental research conducted at Czestochowa University of Technology in Poland indicates that the wavy wall can increase flow momentum near the surface upstream of the trailing edge. Future research will be devoted to reaching the same flow conditions as for wind turbine blade in operation, given by the scales (Relative velocity 60 m/s and boundary layer thickness of 10 cm, which will be a step towards commercialization

Further studies suggest that the method's efficiency under off-design conditions reduces device efficiency by only 50%, which is particularly relevant for floating wind turbines where wind inflow conditions are highly unstable.

New findings indicate that a tilted wavy wall, especially one with an uphill side approximately 50% steeper than the downhill side, can increase the skin friction coefficient by up to 30%, helping prevent flow separation under off-design conditions.

Two types of implementations of the wavy surface on offshore wind turbine blades are planned for assessment. The first involves incorporating the wavy surface directly onto the blade during manufacturing, making it an integral part of the blade's structure and enhancing aerodynamic efficiency. The second implementation focuses on retrofitting existing blades with a wavy surface overlay during maintenance and repair, allowing for performance improvements and extending operational lifespan. Both approaches aim to optimize the aerodynamic properties of the blades, thereby increasing the overall efficiency and effectiveness of offshore wind turbines.