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April 24, 2006, 04:40 |
Hi, Im doing my thesis work an
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#1 |
Guest
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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; |
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April 24, 2006, 04:50 |
Hi!
For the first part of y
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#2 |
Member
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 |
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April 24, 2006, 05:06 |
Hi!
Ups, I think your right
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#3 |
Member
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 |
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April 24, 2006, 05:11 |
phi is in general the flux (rh
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#4 |
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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 |
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April 24, 2006, 05:22 |
> what does turbulence->divR(U
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#5 |
Senior Member
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 Navier-Stokes 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 |
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April 24, 2006, 05:42 |
Hi!
As far as I understood
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#6 |
Member
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 |
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April 24, 2006, 05:52 |
Hi!
Next mistake. It should
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#7 |
Member
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 |
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April 24, 2006, 05:58 |
Thanks a lot!
This was big
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#8 |
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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)); |
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April 24, 2006, 06:12 |
No, there is no mistake in Hrv
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#9 |
Senior Member
Hrvoje Jasak
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No, there is no mistake in Hrv's Thesis on page 71.
Hrv
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Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk |
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April 24, 2006, 06:25 |
Hi!
In this case I want to
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#10 |
Member
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 |
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April 24, 2006, 06:32 |
Hmm, my mistake in fact: it sh
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#11 |
Senior Member
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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Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk |
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April 24, 2006, 06:40 |
Hi!
I think div{(overline{U
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#12 |
Member
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 |
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April 24, 2006, 07:02 |
where can I find this PhD thes
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#13 |
Guest
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where can I find this PhD thesisk. It sounds like Ive could use a thing or two from it?
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April 24, 2006, 07:30 |
You can try the FOAM CFD resou
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#14 |
Senior Member
Hrvoje Jasak
Join Date: Mar 2009
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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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Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk |
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April 2, 2008, 08:59 |
hi to all,
I m a beginner i
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#15 |
Guest
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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 |
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April 2, 2008, 09:01 |
hi to all,
I m a beginner i
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#16 |
Guest
Posts: n/a
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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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