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November 27, 2009, 08:15 
nutWallFunction questions

#1 
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Anonymous
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I'm investigating the wall function approaches used in OpenFOAM. Epsilon and omega wall functions were fairly straightforward in the end. However, I am looking at nutWallFunction and I'm at a loss as to why nut at the wall is defined as so:
nutw[faceI] = nuw[faceI]*(yPlus*kappa_/log(E_*yPlus)  1.0); //for y+>11 Why not use the values the computed values of k, epsilon, or omega? 

November 29, 2009, 04:51 

#2 
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Mark Olesen
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November 29, 2009, 15:03 

#3 
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Anonymous
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Sorry to have confused you; I'll elaborate more. In the kepsilon and komega models, the very last thing they do is compute nut:
//from RealizableKE // Recalculate viscosity nut_ = rCmu(gradU, S2, magS)*sqr(k_)/epsilon_; // (1) nut = Cmu*k/omega nut_.correctBoundaryConditions(); nut is computed as I'd expected here. Why not use the same equation in nutWallFunction to compute the value at the boundary, as you have k, omega, and epsilon already computed at the boundary face? Is it because you require a general expression for application to all turbulence models? The reason I've asked is because I'm not particularly conversant in wall functions and I wasn't expecting a different equation for nutWallFunction. 

November 30, 2009, 05:09 

#4 
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CHB
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November 30, 2009, 06:36 

#5 
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Anonymous
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Thanks, Christof.
"At the walls nutw[faceI] = nuw[faceI]*(yPlus*kappa_/log(E_*yPlus)  1.0); is used to apply the wall shear stress tau_wall = rho * (nu + nut) * du/dy according to the log law. " Ok, if that's the case, then this is a different form from what I've read other people doing in the past. Thank you, anyway, for helping clear that up. 

July 28, 2010, 09:11 

#6 
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Alessandro
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Hi to everybody,
i was looking for the "origin" of this nut equation, It's from: nut=nu*[(Y+/U+)1] and U+=1/k*ln(E*Y+) ??? I don't know the origin of the first equation, I have read PopeTurbulent Flows but in that book nut=k*y*u_t Thank in advance Alessandro
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August 11, 2010, 03:49 

#7  
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Alessandro
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Quote:
thanks
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October 13, 2010, 05:08 

#8 
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Alessandro
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October 28, 2011, 05:30 

#9 
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Anne Gerdes
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Hey Alessandro,
in this thread you might find help: http://www.cfdonline.com/Forums/ope...function.html 

October 28, 2011, 06:36 

#10  
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Anne Gerdes
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Quote:
Dear madad, can you please explain how the nut computed by the nutWallFunction applies the wall hear stress according to the log law? Am I right that there is no explicit near wall treatment for the velocity and the wall function is only enabled via omega, k and nut? Thank you for an answer in advance. Anne 

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