Wind Turbines Spacing Guidelines Review and Wake Region Analysis Based on a CFD Simulation of a Wind Turbine Blade

Abstract

Abstract Guidelines for Wind Turbine Generators (WTG) spacing are not consistent. Several authors have proposed different rules of thumb for such spacing in order to find the minimum distance between WTGs while avoiding the wake effects downwind from each unit which would reduce the overall efficiency of a wind farm. There is an economic impact due to WTG spacing as development land (on-shore or off-shore) may be limited in some cases hence benefitting from maximizing the number of WTG units per area while retaining each unit's performance. While WTG spacing may need case-by-case analysis especially for challenging topographies, there is room for improvement on WTG spacing even while using some of the available commercial software. Computational Fluid Dynamics (CFD) is an essential tool that can help understand the coupled fluid-WTG interactions as the wind affects turbines blades deformation and stresses, and as the WTG creates a wake region downwind of each unit, so potentially diminishing the performance of other units. A CFD model has been used as a tool to understand the interactions of the wind turbine blades with the wind flow domain and its effects on velocity streams and turbulence decay. The model only includes the effects of the blades, and it assumes that the effects of the tower, nacelle and other components are negligeable. Results from the CFD model show insights in the development of velocity streamlines from the interaction against the turbine blades and how the streamlines evolve downwind in the near vicinity a few rotor diameters immediately after the WTG location. Additionally, mapping of the eddy viscosity in the same region downwind the WTG, provides information pertinent to the turbulence created by the interaction between the wind and the blades and how this turbulence is dissipated as a function of distance from the WTG until reaching values similar to the upstream and far distance conditions. The use of CFD, although computationally demanding for simulations of the scale of a wind turbine farm, can provide more details to improve the guidelines and rules of thumb used in the literature by monitoring other fundamental fluid mechanics variables including the eddy viscosity. Improvements on future wind turbine farms spacing criteria should include a combination of experimental data, large-scale modeling and detailed CFD modeling results in the near region downwind of a WTG as each of these approaches may help to achieve a more robust and complete guideline.