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-   -   Wall Roughness (http://www.cfd-online.com/Forums/fluent/97782-wall-roughness.html)

pmbov February 24, 2012 15:45

Wall Roughness
 
I am trying to get a better understanding of what the "Wall Roughness" box is (in the wall boundary layer box) referring to.

Roughness Height:
Is this the height found on standard charts? (see http://www.engineeringtoolbox.com/su...cts-d_209.html).

i.e. If I was to use Stainless Steel than the Roughness Height would be k=5E-5ft.

Roughness Constant:
Is the roughness constant the number calculated (relative roughness).

i.e. Using the hydraulic diameter (d=23.5in), and k. Equation is r=k/d == having a value of 26E-6.

Can someone please help?
Thank you!
Paul

ghost82 February 24, 2012 15:57

Hi,
You are right for the roughness height, but roughness constant isn't relative roughness: fluent uses this parameter to specify uniformity of roughness: since there is no indication on how to calculate it, you have to try and see if your simulation results approximate your experimental results; roughness constant=0,5 indicates a uniformal roughness; use values between 0,5 and 1 to specify non uniformal roughness.

Daniele

pmbov February 24, 2012 16:54

Thank you Daniele, I appreciate your very quick responds.:)


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