A review of wind turbine-oriented active flow control strategies

• Published in: Experiments in fluids 2017-10, Vol.58 (10), p.1-21, Article 134
• Main Authors: Aubrun, Sandrine, Leroy, Annie, Devinant, Philippe
• Format: Article
• Language: English
• Subjects: Active control; Actuators; Aerodynamic loads; Aerodynamics; Aeronautics; Aircraft components; Circulation; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Flaps; Flow control; Fluid mechanics; Fluid- and Aerodynamics; Heat and Mass Transfer; Horizontal Axis Wind Turbines; Life span; Load fluctuation; Mechanics; Optimization; Physics; Review Article; Rotor blades; Rotor blades (turbomachinery); Rotors; Time; Turbines; Wind power; Wind turbines
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-017-2412-0

To reduce the levelized cost of energy, the energy production, robustness and lifespan of horizontal axis wind turbines (HAWTs) have to be improved to ensure optimal energy production and operational availability during periods longer than 15–20 years. HAWTs are subject to unsteady wind loads that generate combinations of unsteady mechanical loads with characteristic time scales from seconds to minutes. This can be reduced by controlling the aerodynamic performance of the wind turbine rotors in real time to compensate the overloads. Mitigating load fluctuations and optimizing the aerodynamic performance at higher time scales need the development of fast-response active flow control (AFC) strategies located as close as possible to the torque generation, i.e., directly on the blades. The most conventional actuators currently used in HAWTs are mechanical flaps/tabs (similar to aeronautical accessories), but some more innovative concepts based on fluidic and plasma actuators are very promising since they are devoid of mechanical parts, have a fast response and can be driven in unsteady modes to influence natural instabilities of the flow. In this context, the present paper aims at giving a state-of-the-art review of current research in wind turbine-oriented flow control strategies applied at the blade scale. It provides an overview of research conducted in the last decade dealing with the actuators and devices devoted to developing AFC on rotor blades, focusing on the flow phenomena that they cause and that can lead to aerodynamic load increase or decrease. After providing some general background on wind turbine blade aerodynamics and on the atmospheric flows in which HAWTs operate, the review focuses on flow separation control and circulation control mainly through experimental investigations. It is followed by a discussion about the overall limitations of current studies in the wind energy context, with a focus on a few studies that attempt to provide a global efficiency assessment and wind energy-oriented energy balance.