# wall roughness

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 June 3, 2009, 05:06 wall roughness #1 New Member   Eric Join Date: Apr 2009 Posts: 23 Rep Power: 9 hi! can anyone tell me how to define wall rougness parameters(Roughness Height and Roughness Constant)? the diameter is 27mm. roughness is 2%. is that to say the Roughness Height is 5.4e-4? thanks!

 June 3, 2009, 12:41 #2 New Member   mj sharawi Join Date: May 2009 Posts: 14 Rep Power: 9 Hi Eric, I've never heard of something like that, but here is what I would do if I were you (I am not sure if your case is as simple as in my mind): I will try to include the effect of roughness with a "momentum sink" added to the momentum equation. regards, MJ

June 3, 2009, 21:04
#3
New Member

Eric
Join Date: Apr 2009
Posts: 23
Rep Power: 9
Quote:
 Originally Posted by mj_no7 Hi Eric, I've never heard of something like that, but here is what I would do if I were you (I am not sure if your case is as simple as in my mind): I will try to include the effect of roughness with a "momentum sink" added to the momentum equation. regards, MJ
hi! thanks
can you explain the meaning "momentum sink"!
it is also my first time to hear the "momentum sink"!
thanks...........

 June 4, 2009, 05:37 #4 New Member   mj sharawi Join Date: May 2009 Posts: 14 Rep Power: 9 Hi Eric, Go to: Define => Boundary Conditions. . . , choose your fluid zone. in the window, activate source terms. Then you can add negative source terms in the x-momentum and y-momentum equations (if you are using axi-symmetric, axial and radial momentums). Don't ask me how to calculate them for your case, I don't know , as I said; this was just an idea. Maybe you can refere to the friction factor correlations and find something out. I hope this helps a little. MJ

 June 4, 2009, 14:46 #5 New Member   mj sharawi Join Date: May 2009 Posts: 14 Rep Power: 9 I forgot to say something, if you are not familiar with sources terms, adding a negative source term (which is a sink term) is equivalent to increasing the pressure drop the in the axis of intrest. Regards, MJ

June 4, 2009, 20:24
#6
New Member

Eric
Join Date: Apr 2009
Posts: 23
Rep Power: 9
Quote:
 Originally Posted by mj_no7 I forgot to say something, if you are not familiar with sources terms, adding a negative source term (which is a sink term) is equivalent to increasing the pressure drop the in the axis of intrest. Regards, MJ
so kind you are !i would consider your' beautiful 'ideas!
thanks

 June 5, 2009, 00:19 tried looking at Fluent Documentations #7 New Member   Javier Larrondo Join Date: Jun 2009 Posts: 17 Blog Entries: 1 Rep Power: 9 Hi, Sorry if I am asking the obvious, but have you tried looking at Fluent Documentation.? I've found several information on this on the following link to Fluent doc... file:///usr/Fluent.Inc/fluent6.3.26/help/html/ug/node253.htm#33285 Also they make reference to the following book, which have the formulas that you are looking for. T. Cebeci and P. Bradshaw. Momentum Transfer in Boundary Layers. Hemisphere Publishing Corporation, New York, 197 Cheers, Javier

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