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April 24, 2006, 04:40 
Hi, Im doing my thesis work an

#1 
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Hi, Im doing my thesis work and need to know which the governing equations are for the simpleFoam application.
If I understand the code correctly it should be: div(phi, U) + turbulence>divR(U)= grad(p)); where: phi is the potential of U (but it has the dimension m³/s?) what does turbulence>divR(U) represent? what does the following lines do? volScalarField AU = UEqn().A(); U = UEqn().H()/AU; 

April 24, 2006, 04:50 
Hi!
For the first part of y

#2 
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Andreas Hauffe
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Hi!
For the first part of your question I can help you. In the Programmer's Guide on page 54 you can see this equation. R is just nueff*grad(U) and nueff is nu+nut and is calculated by the turbulence model. Phi should be U in this case. And the p is pressure/density. Andreas 

April 24, 2006, 05:06 
Hi!
Ups, I think your right

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Andreas Hauffe
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Hi!
Ups, I think your right with phi. It is the potential of U. But part of the discretised form is multiplyed with a surface value because of the surface integrals, right? Andreas 

April 24, 2006, 05:11 
phi is in general the flux (rh

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stefan
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phi is in general the flux (rho*u)
>what does the following lines do? >volScalarField AU = UEqn().A(); >U = UEqn().H()/AU; This lines are need to precondition (jacobian) the U matrix. hth 

April 24, 2006, 05:22 
> what does turbulence>divR(U

#5 
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Gavin Tabor
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> what does turbulence>divR(U) represent?
This is the turbulence modelling. When you average the NSE you get back a very similar set of equations  the Reynolds Averaged NavierStokes equations  which have one additional term, which represents the effect of the fluctuations around the average (the turbulence) on the mean flow. We usually write this as div(R) where R is a 2nd rank tensor (the Reynolds Stress). Since we don't know this term (the closure problem) we need to model this; which is usually done by assuming that the turbulence has a dissipative effect and creating a 'turbulent viscosity' (which is usually so large it swamps the physical viscosity) and write R=nu grad(u). In FOAM this all gets swallowed into the turbulence model; turbulence>divR is getting this out of the model in a convenient (and mathematically stylish) way. Gavin 

April 24, 2006, 05:42 
Hi!
As far as I understood

#6 
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Andreas Hauffe
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Hi!
As far as I understood these things in this case div(R) is not only the Reynolds stress tensor of the RANS equations. But it is only a question of definition I think. div(R) = laplacian(nu,U) + Reynolds stress tensor Andreas 

April 24, 2006, 05:52 
Hi!
Next mistake. It should

#7 
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Andreas Hauffe
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Hi!
Next mistake. It should be div(R) = laplacian(nu,U) + div(Reynolds stress tensor) There is a mistake in Hrv's PhD. Thesis on page 71. Andreas 

April 24, 2006, 05:58 
Thanks a lot!
This was big

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Thanks a lot!
This was big help. I will follow my papers on Reynolds equation on average flow values. a thought isnt div(UU)=2U*div(U) which would give 1/2*div(phi, U) + turbulence>divR(U)= grad(p)); 

April 24, 2006, 06:12 
No, there is no mistake in Hrv

#9 
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Hrvoje Jasak
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No, there is no mistake in Hrv's Thesis on page 71.
Hrv
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April 24, 2006, 06:25 
Hi!
In this case I want to

#10 
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Andreas Hauffe
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Hi!
In this case I want to apologise to you for my mistake. But for my understanding I have to ask why in equation (2.30) the Reynold stress tensor is just added? So this equation consits of 5 vectors and a tensor. Where is my mistake? Andreas 

April 24, 2006, 06:32 
Hmm, my mistake in fact: it sh

#11 
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Hrvoje Jasak
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Hmm, my mistake in fact: it should say div{(overline{Uprime Uprime})} right? and I am missing the div.
Will fix it asap. Hrv
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April 24, 2006, 06:40 
Hi!
I think div{(overline{U

#12 
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Andreas Hauffe
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Hi!
I think div{(overline{Uprime Uprime})} is right. But your PhD thesis is just a great work to understand what OpenFOAM does. And in comparison to stupid things I'm telling sometimes it is without mistakes! Andreas 

April 24, 2006, 07:02 
where can I find this PhD thes

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where can I find this PhD thesisk. It sounds like Ive could use a thing or two from it?


April 24, 2006, 07:30 
You can try the FOAM CFD resou

#14 
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Hrvoje Jasak
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You can try the FOAM CFD resource site http://www.foamcfd.org  there's quite a lot of stuff there including a bunch of PhD Theses done with OpenFOAM I managed to get in electronic form. Alternatively, you can try my personal web pages on http://www.h.jasak.dial.pipex.com.
Enjoy, Hrv
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April 2, 2008, 08:59 
hi to all,
I m a beginner i

#15 
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hi to all,
I m a beginner in OpenFoam and I want to program fluctuations with tensor... for example I want the following program to do with fluctuations. magSqr(fvc::grad(U))+ sqr(gradU.component(tensor::YX) + gradU.component(tensor::XY)) does someone can help me? best regards 

April 2, 2008, 09:01 
hi to all,
I m a beginner i

#16 
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hi to all,
I m a beginner in OpenFoam and I want to program fluctuations with tensor... for example I want the following program to do with fluctuations. magSqr(fvc::grad(U))+ sqr(gradU.component(tensor::YX) + gradU.component(tensor::XY)) can someone help me? best regards 

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