
[Sponsors] 
October 26, 2009, 11:19 
nutWallFunction boundary condition

#1 
Member
Join Date: Sep 2009
Posts: 45
Rep Power: 8 
Hi all,
I use a turbulence model (RANS) and I need you for one thing: I know that "nut" is calculated by the formula nut=C*k^2/epsilon where C=0.09. I've seen over some tutorials: " type nutWallFunction; value uniform 0; " and my problem is here, why does the value set to 0 ? Indeed, nut is not equal to 0 near the wall if we consider the formula above. Could somebody explain that to me ? thank you in advance 

October 27, 2009, 16:37 

#2 
Member
Paulo Alexandre Costa Rocha
Join Date: Mar 2009
Posts: 71
Rep Power: 8 
Dear AirS,
I think nut goes to zero when the turbulence kinetic energy (k) goes, based on the zero velocity on the wall. Best Regards, Paulo 

November 4, 2009, 07:10 

#3 
Member
Join Date: Sep 2009
Posts: 45
Rep Power: 8 
Thanks for answering but I'm sorry to not understand:
the turbulent kinetic energy near the wall is modelled by the kqRWallFunction and its value is set to uniform but it's not equal to zero, it's even equal to the intial condition that I could compute before (cf. tutorials) So, is that correct if I say that NEAR the wall the turbulent kinetic is not equal to zero on account of the model but that ON the wall it's fixed to zero by the condition "value uniform 0" ?? it doesn't make sense but I don't know what it could be otherwise. Hope you can help me guys to sort this out. Thanks! 

January 22, 2010, 10:49 
nutWallFunction or calculated nut

#4 
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 13 
Hi FOAMers,
this seems the good thread for posting a question that have been turning round into my mind for a couple of days now. I am wandering what is the difference in using nutWallFunction or a { type calculated; value uniform 0; } condition for nut if k and epsilon are defined as kQRWallFunction and epsilonWallFunction in the same boundaries. The only explanation I see is that:
Thanks a lot to those that will shed some light. Maddalena 

March 2, 2010, 08:56 
??

#5 
Senior Member
Sandy Lee
Join Date: Mar 2009
Posts: 207
Rep Power: 9 
Then, what is the conclusion? ...
Who can give light? 

March 3, 2010, 07:28 

#6 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 12 
The
value uniform 0; entry is simply a placeholder for that gets filled with the correct value of nut by the code once you run it. To be clear, the initial value of nutw = 0 has no effect on the solution, it is where the result of calculating nutw will get written in the result fields. It is not an input field in the normal sense of the word, but rather an output field that just needs to be there in the beginning because of the way the code is written. 

March 3, 2010, 08:31 
Light!

#7 
Senior Member
maddalena
Join Date: Mar 2009
Posts: 436
Rep Power: 13 
Hello Sandy, besides Eugene's explanations, you can find some more information about the question I posted above on this thread: http://www.cfdonline.com/Forums/ope...tml#post243652. Hope this help. maddalena 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Boundary Conditions  Thomas P. Abraham  Main CFD Forum  20  July 7, 2013 05:05 
Axis Boundary Condition..what is it?  CFDtoy  FLUENT  6  February 13, 2007 06:51 
How to set boundary condition in Fluent for the fo  Peiyong  FLUENT  1  November 10, 2006 12:44 
1 and 2 Order Boundary condition at the same place  CFD_Flo  Main CFD Forum  4  July 11, 2005 11:57 
How to resolve boundary condition problem?  sam  FLUENT  2  July 20, 2003 02:19 