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 Aerospace June 8, 2011 11:08

wall Functions based on Aerodynamic roughness

Hello everybody,

I would like to know if there is any available wallFunction in openFoam wich employs the aerodynamic roughness instead of sand roughness for the K-epsilon model o any other turbulence model.

Thank you very much in advance.

 Aerospace June 2, 2012 07:25

Hello!

In the last OpenFOAM release (OF 2.1.1), the announce says:

A new nuAtmRoughWallFunction wall function model, specialised for
atmospheric velocity profiles has been added in 2.1.1.

I glance the code and the new function seems to be using directly the aerodinamic roughnes value of the terrain Z0. So this function, doesn't requires the sand grain value? it can just employ the aeodynamic roughness value?

Anyone knows if this is ok?

 fs82 June 4, 2012 08:12

1 Attachment(s)
Within the field of meteorology the usage of z0 is quite common. Normally one uses the Monin-Obukhov relationship, but for incompressible flows with neutral stability (no temperature induced buoyancy effects) this relationship reduces to the common known logarithmic law for rough walls, which could be found in every textbook, e.g. boundary layer theory of Schlichting. z0 is a displacement height, e.g. in small scale simulations it represents a grass layer or in large scale simulations a whole forest. I do not really know what is implemented in nuAtmRoughWallFunction but a logarithmic wall law is really easy to implement. I have attached my version, but it is used for LES (nuSGS). But you should be able to change nuSGS to nut for RANS simulations.

Best regards,
Fabian

 fs82 October 16, 2012 09:20

1 Attachment(s)
There is a serious bug in the wall function. I fixed it in the attached version.

 letzel March 1, 2013 12:23

Dear Fabian,

my target is to perform urban LES, i.e. LES with a rough bounding surface (bottom, building walls, pitched roofs). I would like to use different meteorological roughness lengths for the different types of bounding surfaces.

I would like to ask you the following questions:
1. Can your code be applied to different types of bounding surfaces with individual settings (e.g. different z0 for bottom, building walls, pitched roofs)?
2. Do you also provide a wall function for U in a similar fashion, or do you use one of the existing wall functions instead?
3. Could you kindly provide a sample case set-up so that I could better understand how to apply your wall function code in practise?
4. Can your code deal with non-horizontal surfaces (such as building walls, pitched roofs)?