If we have wind speed data for 10m height, one can calculate (forecast) wind at higher altitude using power law formula; V(z)=Vr(Z/Zr)^2
where V(z) is speed of wind at required height Z, Vr is wind speed at reference height Zr and β is surface roughness length.
If wind speed at reference height, let say at 10m, is zero then it will also be zero at required height (let's say 80m or 100m) by using the above equation, which seems unrealistic.
Practically there is no possibility of zero wind speed at no point and hence the power law is practically suitable to calculate the wind speed at various heights.
Alternatively another formula can be used to calculate wind speed at various height.
V=(Vt/k).ln(h/Z0).
where, Vt is the friction velocity, V is the wind speed at height 'h', 'k' is the Karman constant (~0.4) and Z0 is the roughness length. Terrain roughness could be obtained from various sources of particular geographical location to find out Z0.
Dear Ramesh sb, Thank you very much for your answer... Can you please tell me about friction velocity?
Friction velocity is also called shear stress velocity and is defined as the square root of the ratio of Reynolds stress to density. If you think of the surface wind stress as the vertical transfer of horizontal momentum, then the friction velocity can be thought of as the magnitude of the velocity fluctuations in a turbulent boundary layer flow. I don't know how much that helps you, because I'm used to working in an air-sea environment where you can have significant momentum fluxes. You might get more help from Mark Bourassa's web tutorial about wind and stress (http://coaps.fsu.edu/~bourassa/scat_html/forcing_tut/forcing_tutorial.html), or (if you are working over the ocean) a book by Jones and Toba called Wind Stress over the Ocean (2001).
if you main "extrapolation", you can find many researchs in this subject specially by using artificial intelligence methods.
(I still make my first steps in research)
there are 2 ways to evaluate the wind speed at higher elevation:
1- by doing vertical extrapolation of the mesured wind speed
2- by doing vertical extrapolation of the 2 Weibull parameters
Justus and Mikhail are among the pioneers and have done several studies.
you can find several methods for the wind speed extrapolation in 2 articles of Giovanni Gualtieri and Sauro Secci who have summarized the differents mothods:
- Comparing methods to calculate atmospheric stability-dependent wind speed profiles: A case study on coastal location: Renewable Energy 36 (2011) 2189-2204
- Methods to extrapolate wind resource to the turbine hub height based on power law: A 1-h wind speed vs. Weibull distribution extrapolation comparison: Renewable Energy 43 (2012) 183-200
good continuation
There are two methods one as told by u
and other way is to use weibell distribution
wind speed is always greater than zero
Dear Mahesh can you please give your answer in detail and tell me how wind speed will always be zero by using weibull distribution.?
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