TurbSim: EWM

Wind & Water Inflow Turbulence
1

Hello everyone,

I have a doubt about TurbSim. I want to calculate the turbulent winds using the KAIMAL turbulence spectrum according IEC 61400-1 (ed3).

In order calculate the EWM to load cases 6.1 , the certification entity said that the EWM have to be defined like

  • A Three dimensional three component anisotropic Kaimal turbulent field (10 minute sample) with mean wind speed set to 50 year return ten minute mean Vref (42.5 m/s ClassII)

and also they ask an other requirement,

  • The longitudinal turbulence intensity at hub height set have to achieve a moving 3-second mean of the expected extreme wind speed with a recurrence period of 50 years Ve50 (59.5m/s ClassII), at any position within the swept rotor area.

I don’t know if this last requirement is possible comply with TurbSim (to obtain in the 10 minute wind file 3s gust wind speed above Ve50). Could you give me your opinion about that? If the answer is negative what would be the way to do it?

Thanks in advance

Best regards

Alfredo

2

Hi, Alfredo.

If you use the EWM for Class II in TurbSim by setting IEC_WindType to “2EWM50”, it will set the turbulence intensity to 11%, which is the value specified in Eq. 16 of IEC 61400-1 Ed. 3.

I ran the code with a couple of seeds, and then calculated the 3-s maximum wind speeds at all the points on the grid. The value was slightly less than Ve50 and changed slightly with different seeds.

If you are required to use a different turbulence intensity, you will have to set the following parameters in the TurbSim input file:
IEC_WindType = “NTM”
URef = 42.5 m/s
PLExp = 0.11
IECTurbC = [user-specified] %

If you use IECTurbC = 11% (and all other inputs the same), you should get the same results as setting IEC_WindType to “2EWM50”.

Hope that helps.

Regards,
Bonnie

3

Hi Bonnie

Thank you for your answer.

If I want to achieve a moving 3-second mean of Ve50 (59.5m/s ClassII) at any position within the swept rotor area, I would have to calculate a NTM changing the turbulence intensity until achieve the value (I suppose the turbulence intensity will be higher than 11%)

My doubt is how I could calculate the 3-second mean maximum wind speeds at all the points on the grid in order to verify if the turbulence intensity is enough or no. What type of a output file I would have to use?

Thanks

Best regards

Alfredo

4

Hi, Alfredo.

The TurbSim archive has some Matlab scripts in the Test folder that can read the various output files. If you are using the Bladed-style .wnd files, you can use readBLgrid.m to get the velocity at all the grid points.
If it helps, here is my Matlab code that I used to get the maximum 3-s running average u-component wind speed at each point on the grid:

[code][velocity, y, z, nz, ny, dz, dy, dt] = readBLgrid( ‘EWM50.wnd’ );

ns = 3/dt; % number of samples in 3 s.
filterAry = ones(1,ns)./ns; % filter for 3-s running average

max3s = zeros(ny,nz);
for iy = 1:ny
for iz = 1:nz
u = velocity(:,1,iy,iz);
u_f = filter(filterAry,1,u);

    max3s(iy,iz) = max(u_f);      
end

end[/code]