CFD Modeling of a Vertical Axis Wind Turbine using Actuator Cylinder Theory

This paper studies the flow field and power generation from a Vertical Axis Wind Turbine (VAWT) by extending the Actuator Cylinder Model to include the viscous effects. Turbulent flow effects in the actuator cylinder model are modeled by solving the Reynolds-Averaged Navier-Stokes (RANS) equations with the Spalart-Allmaras (SA) turbulence model in ANSYS FLUENT. A study is performed to establish mesh independence of the solutions. Numerical solutions on a fine mesh are compared to existing theoretical results based on inviscid theory for a series of flow conditions and turbine sizes. Similar trends in the present turbulent flow results are found as in the inviscid results for downstream velocity and pressure profiles. The Betz limit is found not to be applicable to the Vertical Axis Wind Turbines. To consider wake interactions, the Actuator Cylinder Model is extended to two turbine cases. Differences between the present numerical results and inviscid theory are discussed

New System for the Acceleration of the Airflow in Wind Turbines

Background: This patent is based on the wind industry technology called Diffuser Augmented Wind Turbines (DAWTs). This technology consists of a horizontal axis wind turbine, which is housed inside a duct with diverging section in the direction of the free air stream. In this paper, a review of preceding patents related to this technology is carried out. Objective: This paper presents an innovative patent to improve the performance of horizontal axis wind turbines. In particular, this system is aimed at improving the performance of those turbines that otherwise might not be installed due to the low wind resource existing at certain locations. Methods: The most innovative elements of this patent are: (1) the semi-spherical grooves, which are mechanized on the surface of the two diffusers in order to guarantee a more energetic boundary layer; (2) the coaxial diffuser, which is located downwind following the first diffuser in order to increase the suction effect on the air mass close to the inlet; (3) the coaxial rings located around the first diffuser outlet, which are used to deflect the external airflow toward the turbine wake; and (4), the selforientating system to orientate the system by the prevailing wind direction. Results: An application of the patent for increasing the power generated by a horizontal axis wind turbine with three blades is presented. The patent is designed and its performance is evaluated by using a Computational Fluid Dynamics code. The numerical results show that this system rises the airflow going through the rotor of the turbine. Conclusion: The patented device is an original contribution aimed at enabling a more profitable installation of wind turbines in places where the wind resource is insufficient because of the wind shear caused both by the proximity of the earth and the obstacles on the earth surface.This work was supported by the OASIS Research Project that was cofinanced by CDTI (Spanish Science and Innovation Ministry) and developed with the Spanish companies: Iridium, OHL Concesiones, Abertis, Sice, Indra, Dragados, OHL, Geocisa, GMV, Asfaltos Augusta, Hidrofersa, Eipsa, PyG, CPS, AEC and Torre de Comares Arquitectos S.L and 16 research centres. The authors also acknowledge the partial funding with FEDER funds under the Research Project FC-15-GRUPIN14-004. Finally, we also thank Swanson Analysis Inc. for the use of ANSYS University Research programs as well as the Workbench simulation environment

Review of design conditions applicable to offshore wind energy systems in the United States

Offshore wind turbines are now being considered for use in the United States. Ensuring proper design of offshore wind turbines and wind farms requires knowledge of the external conditions in which the turbines and associated facilities are to operate. The primary external conditions are due to the wind and waves. Also, for many locations, floating ice will also be a major factor in the design. This review examines the following aspects of external conditions for the design of offshore wind turbines for the United States: (1) design requirements, (2) available offshore data sources, (3) data estimation and extrapolation techniques, (4) on-site data collection, and (5) likely sources of extreme events, including hurricanes and northeast storms.Offshore wind Wind turbine design Offshore wind systems data