nutRoughwallfunction arguments
 

Hi Openfoamers,

I would like to know what the last item represents in the following dictionary entry in 0/nut:
walls { type nutRoughWallFunction; Ks uniform 1e-5; Cs uniform 0.5; value uniform 1.0;}

Does it mean that nut is assigned a fixed value of 1 on the 'walls' patch throughout the entire simulation and Ks and Cs completely ignored? Or is nut assigned a value of 1 for the first time-step on the 'walls' patch?

I took a look at nutRoughWallFunctionFvPatchScalarField.C and nutRoughWallFunctionFvPatchScalarField.H, but could not see how the last dictionary entry was used.

Thank you,
George

Hi
It seems like in OF 2.0.1 the function nutRoughWallFunction is now nutURoughWallFunction, and the arguments have changed. They are now
value
roughnessHeight
roughnessFactor
roughnessConstant

I understand what roughnessHeight refers to, but can anyone explain what exactly the other arguments change. Can't find a definitive answer anywhere in the forums.
Thanks
Case

Hi,

You can also use nutkRoughWallFunction in OF2.0. I use the turbineSiting tutorial and just change Ks and Cs to my case.

Regards

I tried to run one of my old cases made when I was using OF1.7.1 that uses nutRoughWallFunction, butgot an error message, giving me a list of the possible patches that are allowed, with nutURoughWallFunction being one of them. Had to change to nutURoughWallFunction, and also change the arguments.

Hello!

Did you get an answer?
Thanks for sharing!

I give it a try: scalarField& y = rasModel.y()[patchI]...that returns the near wall distances.

scalar dKsPlusdYPlus = roughnessHeight_/y[facei]

...is the ratio of roughness heigt to the near wall distance of patchI

dKsPlusdYPlus *= roughnessFactor_

...used for tuning this ratio to finally:

yp*dKsPlusdYPlus

...get the nondimensional roughness heigt based on the y+ value of the latest timestep.

I use roughnessFactor = 1.

roughnessConstant is only applied (as a multiplier) if the nondimensional roughness is bigger than 90, so I guess it is
about the issue of where the different regions of the wall velocity profiles are placed, viscid layer, log layer etc.

These are guesses by reading the source code. For generally understanding of the rough wall function, see the Thesis of
John O’Sullivan, February 2012, "MODELLING WIND FLOW OVER COMPLEX TERRAIN", especially eq. (2.55). He worked with OpenFOAM

Dear all,
Tell me where I can find the theoretical description of function nutURoughWallFunction?