# Assigning Wall Roughness in STAR-CD

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 March 8, 2008, 01:51 Assigning Wall Roughness in STAR-CD #1 Sachin Guest   Posts: n/a Hi , I am trying to assign roughness to no slip wall. I could see that there are three constants A , B and C which has by default values of 8.5, 0 and 1 respectively. Then user has to input efective wall roughness(y0) and displancement(D). I went through Manual. Then I did calculate thickness of laminar sublayer. The roughness I want to include corresponds to completely rough wall. My question is that while assigning copletely rough wall, shall I have to just input efective wall roughness (y0) and have to keep everything else (A,B,C and D) as it is ? is this correct what I understood from Manual and reference for wall roughness. Thanks in advance. Thank you for your time and consideration. --------------------------------------------------------------------------------

 March 11, 2008, 12:24 Re: Assigning Wall Roughness in STAR-CD #2 tom Guest   Posts: n/a You may have noticed that this question has been avoided by the board members. To say using the roughness is a black art is an understatement. If you trace back to the original reference you will find that the roughness is actually sand roughness, which is not the same as the roughness on the Moody diagram. My company fianlly gave up and wrote a subroutine to use our own friction based on our roughness models. Tom

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