Wind flow under complex terrain (CFD)
The simulation of wind flow under complex terrain poses a significant modeling challenge. Not only the wind resource variation over the wind farm area is more pronounced but also hazardous wind effects, that can affect the structural turbine safety and their performance, can take place.
Linear, or non-CFD, models (like WAsP or MS-Micro) not provide accurate answers for these sites. They are limited in term of topography, obstacles, forestations and thermal stability effects. A significant investment in more comprehensive simulations must be considered, like those provided by Computational Fluid Dynamics (CFD) solvers.
For these challenging sites MEGAJOULE delivers a peerless solution. The team of MEGAJOULE Inovação in cooperation with ISEP has developed a new tool for wind flow simulation over complex terrain. Windie™ is a CFD code exclusivly used by MEGAJOULE to obtain the most accurate data in order to give advice on how to maximize production and minimize down-times and maintenance costs.
Computational Fluid Dynamics (CFD) – complex wind flow simulation

The mathematical model is based on the resolution of the continuity and momentum equations (Reynolds averaged) with integration of a turbulence model, in steady or transient formulation. Effects caused by topography and obstacles are taken into account as well as the effect of forestation and roughness changes.
A special formulation has been developed and used for modeling forest canopy. The most important modeling results are 3D wind field, vertical wind, wind declination, wind shear and the turbulence.

Windie™ is a new tool for the simulation of three-dimensional flows over complex terrain. The software code is property of Windie Lda and is exclusively used by MEGAJOULE consultants. It stands out from other software codes, due to its advanced forest canopy modelling and its ability to be coupled with mesoscale results, producing much more representative solutions of local wind patterns.
Resource assessment and energy estimates
The CFD wind flow modeling in very complex sites can significantly reduce the uncertainty and risk in wind resource assessment.
The estimate of non-linear effects in wind flow makes it possible to model orographic shadowing and occurrence of stagnation points, forestation effects, etc., that otherwise could be unnoticed. This provides a more accurate base for micrositing and a effective layout optimization.
The CFD modeling results can also be used to select the best sites to conduct wind measurements.
Site assessment

The CFD can provide all major parameters for safety assessment of turbines, namely according to IEC 61400-1: horizontal wind speed, wind flow inclination, wind shear, turbulence intensity and extreme winds.
It is also possible to estimate the effects of very complex features on wind turbines, such as very steep slopes, escarpments, obstacles and forestation.

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