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Simulation of Wind over complex terrain
comparison of CFD codes
Rémi Gandoin, DONG Energy
PO. ID
135
Results
Objectives
Conclusions
Methods
European Wind Energy Conference & Exhibition 2010, Tuesday 20 - Friday 23 April 2010, Warsaw, Poland
normalized speed-up at 80m agl for (left to right) the flat, moderately and steep hills as a
function of the distance from the hill center
WIND
turbulence intensity levels at 80m agl for (left to right) the flat, and moderately steep hills as
a function of the distance from the hill center
The objective of this study is to estimate the uncertainties of the CFD codes
EllipSys3D (Risø-DTU) and MeteodynWT (Meteodyn) in complex terrain.
A mountainous site in Norway has been selected for this purpose. A
comparison with the linear model WAsP has been also conducted.
The models results have been compared with results using standardized site
calibration procedures based on measurements.
It was decided at first to compare both codes, EllipSys3D and MeteodynWT,
on flat terrain in order to discuss the meshing process and the boundary
conditions.
Secondly, WAsP and CFD simulations were run on 2D hills, whose
topography was extracted from a real terrain, in order to quantify the
uncertainties between the models.
Finally, WAsP and CFD codes were run on the real terrain, results were
compared between each other, and with met mast measurements.
This project has identified two main differences between MeteodynWT and
EllipSys3D, namely the mesh resolution and the turbulence models.
The CFD codes were found to capture non linearities, showing a different
behaviour than WAsP, and identifying severe wind conditions. They follow
similar trends in simple and moderately steep terrain. However, EllipSys3D
did predict recirculation after a very steep theoretical profile, while
MeteodynWT did not, presumably because of the limitation in the mesh
accuracy due to the necessary limitations of the 32 bits version of the
software.
At hub height on real terrain, discrepancies were found to be limited, and
within the measurement uncertainties.
To conclude, flat terrain and 2D hill simulations were found to be useful to
explain the real terrain simulations. Even if MeteodynWT on a32bits machine is
a more pre-configured code, and contains limitations, it showed comparable
results with EllipSys3D.
Three topics require further investigations: only one site and two wind directions
were simulated, steep theoretical profiles led to discrepancies between the
codes, measurements were not conducted especially for this project.
Finally the two codes agree fairly well on the identification of unsuitable
turbine locations.
Recirculation
Flat Mid Steep
Flat Mid
180 degrees slices
Gaussian fit
wind data analysis
relative speed difference [%] and
turbulence intensity [%] for each
mast and wind direction
maximum speed-up at the top of the
hill as a function of the slope, in
theoretical terrain