View shear exponents results from simulation

[Andrés]

Hi all, 

I am currently running a simulation of a wind farm and nearby wind farms with different hub heights. I would like to understand and obtain the wind shear exponent that WaSP is using for doing vertical corrections. 

Is it possible to obtain such data, maybe roughness/height dependant? 

 

Thank you very much!

[Mark Kelly]

Hello Andrés,

I should first note that WAsP does not use a shear exponent for vertical extrapolation.
Rather, it uses geostrophically-perturbed similarity theory (i.e. roughness-based with 2 stability parameters, also an adjustment for the upper atmospheric boundary layer).  The WAsP method does vertical extrapolation for both the Weibull-A and k parameters, which are linked; it is not a "wind profile" per se.
It is not designed for shear.

However, if you like, you could simply output the speed (or Weibull-A) at 2 heights, and then calculate the shear using

alpha = ln(U_2/U_1)/ln(z_2/z_1) .

 Indeed it is dependent on roughness and height, as well as e.g. the offset heat flux parameter; the above expression/method is much simpler than trying to use the complicated equation which results from the theory.

with kind regards,
--Mark Kelly, DTU Wind Energy

[Andrés]

Thank you very much Mark for your answer. 

I assume then that the better way to output the speed and see vertical extrapolation only dependent on height (and avoiding or mostly avoiding roughness and offset heat flux parameter corrections), would be to put a test wind turbine on the same location, with different hub heights, is that right?

Thank you very much again.

Best,

Andrés 

[Niels Gylling Mortensen]

Hi Andrés,

You can also explore the wind profile at a site by using scripts in WAsP: Insert a turbine site, select it, and then choose Tools > Utility scripts > ... to see what scripts are readily available. This way of doing it is described further in these course notes.

Hope this helps,

Niels