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Setting atmopheric boundary layer

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Old   July 28, 2016, 14:45
Default Setting atmopheric boundary layer
Almond Wong
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I am trying to understand how to set up an atm boundary layer.

I came across 2 threads that i felt were relevant. However, I would like to clarify something.
Following this thread:
nutRoughWallFunction was used.
Supporting that is this thread: which detailed the specification to be:
type nutRoughWallFunction::Ks;
value uniform 0.001;
type nutRoughWallFunction::Cs;
value uniform 0.5;
However, when I had a look at the turbinesiting tutorial, nutkAtmRoughWallFunction was used instead in this manner:
        type            nutkAtmRoughWallFunction;
        z0              $z0;
        value           uniform 0.0;
I have 2 questions:

1) which is the "more correct" function to depict an ABL?
2) How are Ks and Cs specified through nutkAtmRoughWallFunction or are they somehow accounted for?
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Old   July 28, 2016, 17:02
Almond Wong
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If I were to simulate flow over a city (reasonably defined) using the nutkAtmRoughWallFunction, do I have to define z0 as per required as 2.0 or leave it out as it is already accounted for by the geometry?
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Old   April 12, 2019, 18:31
Andrew O. Winter
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It seems to me that there is a more appropriate set of functions to use for simulating atmospheric boundary layer behavior. I'm working on trying out the BCs for U, k, and epsilon as defined according to

Additionally, there is a different nut BC that can be used to go along with these U, k, and epsilon BCs, which can be read about at

To address your question about z0, you have to set it to something non-zero for the equations to work out since it is used in the denominator of some of them. Thus I think setting it to the "physically correct" value according to the type of terrain roughness you're trying to model even if you're explicitly including those objects is the way to go.
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Old   August 4, 2022, 11:04
Default wall-functions for the ABL
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Juan Carlos
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Hi everyone!

Even though it has been six years ago, I think the next link (from Chalmers University) might be helpful for anyone looking for more answers:

I hope, it helps.

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