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Old   August 18, 2011, 20:27
Default groovyBC, multiple domains
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ak
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Hi

I am a relatively new user of OpenFoam, working in the area of combustion dynamics, and needed some help with transient boundary conditions.

The combustion system is divided into 3 components: the inlet channel (non-reacting flow), the combustor (reacting flow computations in this region), and the exhaust (models acoustics using 1D gas dynamics); the three are to be linked by appropriate boundary conditions (ie coupled at the inlet and exit planes of the combustor).

I saw that groovyBC be used for coupling of patches. The sample case for groovyBC defines 3 regions:
Region A: inlet ; interface11
Region B: interface12 ; interface21
Region C: interface22 ; outlet

However, I am interested in performing the reacting simulations only in the combustor region. Could someone please point out how it may be used for the above case, or if there are other ways to implement it?
Any tips would be useful, as I still learning working with OF!

Thanks so much!
amit
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Old   August 19, 2011, 07:39
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Bernhard Gschaider
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Quote:
Originally Posted by newOFuser View Post
Hi

I am a relatively new user of OpenFoam, working in the area of combustion dynamics, and needed some help with transient boundary conditions.

The combustion system is divided into 3 components: the inlet channel (non-reacting flow), the combustor (reacting flow computations in this region), and the exhaust (models acoustics using 1D gas dynamics); the three are to be linked by appropriate boundary conditions (ie coupled at the inlet and exit planes of the combustor).

I saw that groovyBC be used for coupling of patches. The sample case for groovyBC defines 3 regions:
Region A: inlet ; interface11
Region B: interface12 ; interface21
Region C: interface22 ; outlet

However, I am interested in performing the reacting simulations only in the combustor region. Could someone please point out how it may be used for the above case, or if there are other ways to implement it?
Any tips would be useful, as I still learning working with OF!

Thanks so much!
amit
In short: in the swak4Foam variant of groovyBC it is possible to access data from other meshes (http://openfoamwiki.net/index.php/Co...al_expressions) but I'm not quite sure whether this is what you're after.

A bit longer: With your term "region" I assume that every one of these has a separate mesh. Of course this also means that you have a specialized solver to cope with these (someone like cht-Foam). One problem with groovyBC and "external" expressions is that these only work with "accumulated" values (min, max, average, sum) which means that you will lose all the spatial information. Look at the tutorials for the cht-Solver for a better soluition.

But if your system is physically connected anyway (flow goes through the boundaries) I'd propose to calculate it in one mesh with a solver that captures all the physical features. Most likely the results will be better than explicitly coupling multiple regions via boundary conditions

Bernhard
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Old   August 19, 2011, 10:06
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Thanks so much Bernhard!
I think cht-Solver might just be what I was looking for. I'll look at the possible options and post when I have some results.

Thanks again,
ak
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Old   August 26, 2011, 10:12
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Bernhard Linseisen
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Argh, seems you just look into part of what I hope to do for my thesis, Amit. But nice to know I am not completely alone with my opinions on need-to-know-simulation. ;-)

Bernhard is right, I would suggest you to try to modify chtMultiRegionFoam.
For setting up the case itself a small HowTo and an example case might be helpful which you can find at http://cern.ch/blinseis/_public/openfoam.htm .
Unfortunately I have not yet tested if it is the same procedure with OF 2.0.x, but I'm sure you will find out quickly. ;-)
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Old   August 26, 2011, 10:35
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Thanks for the link, Linse.

Is your system physically connected as well, and are you using a compressible code? In that case, as Bernhard pointed out, one might as well use a single mesh and a solver, rather than split the domain and perform separate computations in each region.
What do you think?

ak
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Old   August 26, 2011, 10:51
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I am sorry for having to say that - but my HowTo has not included anything about the solver yet. It is really only how to set up the geometry for running it with the original chtMultiRegionFoam-solver.

So: Yes, everything is connected within one big Mesh.

What chtMultiRegionFoam does (given the case setup has been done correctly) is applying two different solvers to the different regions. It has hardcoded a solver for a fluid phase (which might be compressible) and a solver for a solid phase.
Maybe you can change these solvers to one including the combustive part and one without the combustion? Changing the region names afterwards should be merely cosmetic...
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