Abstract

Wind turbines will play a crucial role in the global energy transition from a fossil fuel-based world to a renewable-based one. Horizontal-axis wind turbines (HAWTs) currently dominate the commercial sector, although a recent resurgence in interest and research has shown exciting opportunities for the future of vertical-axis wind turbines (VAWTs). Unique cyclical fluid physics results in additional complexity to VAWT blade aerodynamics. Unlike their horizontal-axis counterparts, the rotating blades of a VAWT produce varying torque depending on their location in the circular cycle. The aerodynamic relationship between the incoming wind flow and blade motion is such that the peak power is extracted when the blade and incoming wind are nearly perpendicular to each other during the windward side of the rotor. Recognizing this, the recently conceived dual-vertical-axis wind turbine (D-VAWT) extends a typical VAWT's windward region by having the blades rotate about two vertical axes. Introduced is a new path of purely rectilinear motion connecting the two axes, wherein the blade is designed to achieve optimal aerodynamic efficiency. Initial investigations into the D-VAWT's operation shows promising potential, with power coefficient values in the range of the most efficient VAWTs and even HAWTs. The current study seeks to further improve the performance of the D-VAWT through the incorporation of active blade pitch control throughout the blade path's distinct rotation and rectilinear regions. Computational fluid dynamics (CFD) is used to model a single-blade D-VAWT, and a user-defined method is devised to implement the blade pitch actuation as a function of cycle time location and blade centroid position. Numerical results reveal that strategic blade pitching can indeed increase performance in a specific region of the D-VAWT cycle, however the improvement can create undesired impacts on the flow field in other regions of the rotor. Emphasis is focused on the upstream and downstream flow interaction during active-pitch operation, offering important physical insight to the D-VAWT and VAWTs of similar geometric sizing.