Morphing Segmented Wind Turbine Concept

Abstract

A morphing segmented concept is proposed herein for future extreme-scale wind turbine systems. The morphing may be accomplished by using segmented blades connected by screw sockets and a tension cable system. At low wind and rotor speeds, the segmented blades are fully tensioned and set at high pitch to ensure start-up and maximum power at low speeds. At high rotor rpm, the cable tension can be designed such that centrifugal forces drive the blade segments outward so as to unwind/feather the rotor and prevent over-speed. This effectively acts like a passive pitch control for rotor speeds. Perhaps more importantly, the airfoils of the blade segments can be designed with a center of pressure downstream of the socket axis. This will cause an aerodynamic moment at high wind speeds which will serve to unwind the blade segments to prevent torque spikes and blade stall. For a given rotor diameter and torque, such stall prevention can permit operation at higher average lift coefficient with a reduced blade chord length which can reduce blade and overall system weight. In addition, the segmented blade concept can alleviate manufacturing and shipping constraints for extreme-scale systems. In the proposed concepts, the bending loads will be carried by the segmented rotor spar and not the blade skin. This will result in much larger downstream deflections of the blades at high wind speeds as compared to that of a conventional rigid single-piece turbine blade. Therefore, a downstream design would be needed to avoid potential strike of the blades with the tower. This will require a more aerodynamic tower to reduce wake interactions but a downstream system may eliminate yaw-control and substantially relax blade rigidity constraints, thus further reducing blade weight. However, this morphing concept faces several technical challenges including substantially increased susceptibility to flutter instability and dynamic stall which is expected to require active control systems.