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Old   February 24, 2012, 15:45
Default Wall Roughness
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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

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!
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Old   February 24, 2012, 15:57
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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.

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Last edited by ghost82; February 25, 2012 at 03:44.
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Old   February 24, 2012, 16:54
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Thank you Daniele, I appreciate your very quick responds.
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