# ineffective wall roughness

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 August 7, 2013, 19:15 ineffective wall roughness #1 Senior Member     moein Join Date: Dec 2009 Posts: 132 Rep Power: 10 Hi experts. I'm simulating a weir. I want to know the effect of roughness of weir on velocity. I've done mesh sensitivity analysis and I checked various values of roughness but nothing has been changed. does anyone know where the problem is? any help would be appreciated.

 August 8, 2013, 08:01 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,214 Rep Power: 110 Maybe roughness does not significantly influence your flow?

August 10, 2013, 10:15
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moein
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Quote:
 Originally Posted by ghorrocks Maybe roughness does not significantly influence your flow?
the effect of various roughnesses are the same. roughness of 4 mm, 8 mm and 20 mm!
could it be from fault or inappropriate setting or something else?

 August 10, 2013, 12:07 #4 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,659 Rep Power: 26 How do you specify the roughness parameter in your simulation? Is it part of the wall boundary condition or do you have a geometrical roughness? What about the rest of your setup? Be descriptive! feizaghaee likes this.

 August 10, 2013, 21:34 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,214 Rep Power: 110 Let me state my point a different way. If a hurricane was heading your way, do you think putting a piece of sand paper on the ground would make a difference? What about if you put a piece of sand paper on the ground which had double the surface roughness? Obviously a hurricane is so big it does not matter what you do, the hurricane is going to progress unaffected. So my point is that if the surface roughness does not significantly affect the flow then it does not matter what surface roughness you use you will still get the same result. feizaghaee likes this.

 August 14, 2013, 17:27 #6 Senior Member     moein Join Date: Dec 2009 Posts: 132 Rep Power: 10 thank you all for your replays.

August 14, 2013, 17:30
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moein
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Quote:
 Originally Posted by flotus1 How do you specify the roughness parameter in your simulation? Is it part of the wall boundary condition or do you have a geometrical roughness? What about the rest of your setup? Be descriptive!
it's wall boundary condition. I'm trying geometrical roughness now.

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