TurbSim changing turbulence scale

[Jana.Heppner]

Hi there,

I am simulating the noise characteristics of a SWRT and creating my wind files with TurbSim. Currently I am using the IEC 61400-2 for the TurbSim input file. I am not too familiar with TurbSim and for my simulations I need to use different turbulence scales and I was wondering if there is a way to change the turbulence scale? I don’t necessarily need to use the IEC standard.
Many thanks for your help in advance.

Regards,
Jana

[Bonnie.Jonkman]

Hi, Jana.

There are a lot of ways you can change the turbulence in TurbSim. So, I guess it depends what you mean by “turbulence scale.”

There are several different spectral models to choose from, and each of these give different spectral shapes depending on the input values. If you are using the Kaimal (IECKAI) or von Karman (IECVKM) spectral models, you change the requested turbulence intensity by setting IECturbc to a percentage in the TurbSim input file. For non-IEC models, you can change UStar.

If you want to change the integral scale, it’s a little more difficult, but can be done. Is that what you mean by turbulence scale?

[Jana.Heppner]

Hi Bonnie,

many thanks for your reply.! I saw that it is possible to change the turbulence intensity in the input file what I am trying to change is the turbulence length scale of the inflow wind and wasn’t able to find out how to do that.
I am sorry for not clarifying this properly in my initial question.

Regards,
Jana

[Bonnie.Jonkman]

Hi, Jana.

You can, of course, always change the source code and recompile.

However, TurbSim 1.06.00 has some undocumented features that may help you:

• user-defined uniform spectra
• user-defined von Karman spectra. Here’s some text I wrote in an email to someone asking about this UsrVkm model:

When TurbModel = “USRVKM”:
[list][*]TurbSim uses the IEC von Karman spectra (eq. 25 & 26 in the TurbSim User’s Guide), modified to use local wind speeds (u), standard deviations (sigma), and length scales (L). These “local” values only vary by height.

• The standard deviations and length scales come from a lookup table at the end of the TurbSim input file.
• The sigma profile values are multiplied by the StdScale1, StdScale2, StdScale3 values to get the standard deviations used for each component in the von Karman spectra.
• Heights must be listed in increasing order. Only NumUSRz heights are read, so specify that value correctly!
• TurbSim interpolates linearly between the (first NumUSRz) heights specified in the table; it uses nearest-neighbor before the first and after the last values read.
• Wind speed and direction are from the lookup table only if WindProfileType is “USR” or “default”
• TurbSim reads the values from the “Non-IEC Meteorological Boundary Conditions,” though some parameters may not apply. You should make sure you set the Reynolds stress and coherence parameters so that you get what you want (I think the default values are based on the NWTCUP model for some of those inputs).

WindProfileType = “USR”

• This can be specified for any of the spectral models.
• URef and RefHt input values are not used.
• The wind speed and direction values come from a lookup table at the end of the TurbSim input file.
• Heights must be listed in increasing order. Only NumUSRz heights are read, so specify that value correctly!
• TurbSim interpolates linearly between the heights specified in the table; it uses nearest-neighbor before the first and after the last values read.

[/*:m][/list:u]

I’m in the process of documenting the features in TurbSim v2.0.0. This alpha version has examples in the CertTest folder, and the code is a little more flexible in terms of the coherence models you can use with each of these features. You can test a copy of it here: nwtc.nrel.gov/alphas.

[Jana.Heppner]

That’s perfect! Thanks a lot for your help!

Regards,
Jana