# Rough wall function vs. atmospheric rough wall function

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 September 23, 2015, 07:30 Rough wall function vs. atmospheric rough wall function #1 New Member   Josh Join Date: Jun 2013 Posts: 19 Rep Power: 11 I have been looking into homogeneity of atmospheric boundary layer profiles through an empty fetch. I noticed that nutkAtmRoughWallFunction performed slightly worse than nutkRoughWallFunction. When looking at the code to work out what the atmospheric version was doing, I came across a definition I can't work out: As expected, both define effective viscosity as: $\mu_e = \frac{ \rho C_{\mu}^{1/4}z_P k^{1/2}\kappa}{\log(E^{\prime}y^+)}$ For nutkRoughWallFunction, E' is defined as expected, based on roughness regime. For fully rough (most practical ABL applications), it's: $E^{\prime}=1+K_s^+C_s$ However, for the nutkAtmRoughWallFunction, it is defined as: $E^{\prime}=\frac{z+z_0}{z_0}$. I've not seen this definition in the literature, and can't work out why it's used. It means that the sand grain roughness is never defined in the equation, which seems odd. Can anyone shed any light on this? phuchuynh likes this.

 February 27, 2016, 09:12 #2 Senior Member     Mojtaba Amiraslanpour Join Date: Jun 2011 Location: Tampa, US Posts: 308 Rep Power: 14 Hi, I am working on the same. I can't see the expressions you provided. I have some improves regarding the papers I have reviewed until now. __________________ Learn OpenFOAM in Persian SFO (StarCCM+ FLUENT OpenFOAM) Project Team Member Complex Heat & Flow Simulation Research Group If you can't explain it simply, you don't understand it well enough. "Richard Feynman"

 February 6, 2020, 10:32 #3 Senior Member     Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 11 The last equation corresponds to Eq. 5 from Hargreaves, D. M., & Wright, N. G. (2007). On the use of the k–ε model in commercial CFD software to model the neutral atmospheric boundary layer. Journal of wind engineering and industrial aerodynamics, 95(5), 355-369. DOI:10.1016/j.jweia.2006.08.00 __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

 Tags boundary layer, k-epsilon, wall functions