This paper deals with the 3D effects of a vertical-axis wind turbine caused by the tip vortices. In this study, the VAWT rotor is simplified by the infinitely bladed actuator cylinder concept. The loads are prescribed to be uniform and normal to the surface and are distributed between the upwind and downwind half. Depending on the load configuration, the tip vortices are shed at different locations. This causes the wake induction field and the induction at the rotor to be significantly different. The 3D effects cause a power loss that may go up to 15% depending on the load configuration and aspect ratio. Starting from an aspect ratio of 5, the rotor induction and power is approaching 2D results.

Since the first commercial projects, the development of vertical-axis wind turbines (VAWTs) has been impeded by the limited understanding and inability to accurately model VAWTs. This paper investigates and compares different aerodynamic modelling techniques for VAWTs in 3D. All considered models are using the same blade-element characteristics but use different descriptions to determine the induced velocity field. The H-and Φ-rotor are studied with various aspect ratios and rotor loadings. Both instantaneous azimuthal parameters as well as integral parameters, such as the thrust and power are investigated. The paper concludes that capturing the 3D effects of VAWTs is challenging and the trends to be expected are not straightforward due to the complex vortex system created by VAWTs. All model assumptions affect the results both at the mid-plane of the rotor as well as at the blade tips.

Vertical-axis wind turbines (VAWTs) in double-rotor configuration, meaning two rotors in close proximity, have the ability to enhance the power performance. In this study, we work towards the understanding of vertical-axis wind turbines in double-rotor configuration. Numerical simulations are performed to gain insight in the physics behind the double-rotor concept. Furthermore, a parametric study is performed to explore the effect of the double-rotor lay-out, rotor loading, rotor spacing and wind direction on the flow characteristics and the power generation.