Aerodynamic advances in vertical-axis wind turbines

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As wind farms tend to move towards deeper waters with better wind resources, the classical top-heavy horizontal-axis wind turbines (HAWTs) become particularly challenging. This raises the question whether other concepts could be more suitable and compatible with the deep-sea floating conditions. Hence, the interest in vertical-axis wind turbines (VAWTs) is growing in the search for affordable renewable energy. Vertical-axis wind turbines exchange momentum and energy with the fluid by applying a force field on the flow. The actuation surface, over which the forces are distributed, is cylindrical. The diameter can vary with height as in the Φ-rotor and the surface can be a combination of actuation surfaces nested inside and/or crossing each other. As such, the cylindrical surface provides more freedom than the conventional actuator disk to generate a complex 3D force field varying in space and time. A significant advantage of the cylindrical actuation surface is the ability to distribute forces between the upwind and downwind half and to generate forces perpendicular to the incoming flow. Additionally, the 3D actuation cylindrical surface can be made insensitive to wind direction, eliminating the need for a yaw system. The vertical rotating axis also provides the ability to mount the power generation components near the ground, lowering the centre of gravity and facilitating maintenance.