Wind profile (2005-08-31)

[Old Forum Archivist]

I have a little problem regarding a 40m mast, because the mean wind at 40m is a little lower than the mean at 30m (for all the directions...we have just checked the instruments...): it happens with 2 different masts located on 2 different sites. How I can model this "negative wind shear" in WAsP? I have to suppose a roughness 0.00001?

Thank you very much



Bye

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The mean wind speed profile is the result of the effects of the terrain (elevation differences and roughness changes) and the site climatology. We have seen 'negative wind shears' over hills even with a roughness much higher than the one you mention.



So, first of all, you need to examine your terrain descriptions, ie elevation map and roughness map. Once you are confident that the terrain descriptions are sufficiently detailed and accurate, you may look into other effects - such as the climatological values of the mean heat flux and RMS heat flux. These can be changed in the projects parameter settings and will change the shape of the wind profile. You may enter new values in the WAsP project, corresponding to the climatology at your site, or you can also simply experiment a little - by changing the values - to see the effects on the wind profile. Not knowing your particular site and project, it is difficult to say exactly what should be done, but in general the effects described above are the most important for the wind shear.



The WAsP Team @ Risø

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