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Old   November 28, 2010, 05:21
Lightbulb LRR(Launder-Reece-Rodi RSTM) turbulent model
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Dear Foamers,
I want use LRR turbulent model but i didn't find any sample in tutorial files.
I don't know how is its properties which should be set.
Any suggestion will be appreciated.
Best,
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Old   January 17, 2011, 10:57
Default any success
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Hej,

did you have any success?
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Old   January 17, 2011, 11:04
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Hi,
I used tut files which were k-e. their settings are almost the same. you need to change turbulentProperties from k-e to LRR.
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Old   January 17, 2011, 11:33
Default missing field R
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what is the field R that the calculation requires?
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Old   January 17, 2011, 12:00
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R is reynolds stress tensor. i set it zero fixedValue for inlets, zeroGradient for outlets.
i used kqRWallFunction for walls. i am not sure about this one.
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Old   January 17, 2011, 12:02
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thank you very much, I will try this and come back to this here when I have a result.
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Old   January 20, 2011, 11:51
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it seems to work with those boundary conditions, givig approximately the same results as the non-reynolds stress models. the results are slightly improved over the standard k-epsilon
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Old   January 20, 2011, 11:55
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I have same problem. i don't know why its result is approximately same as k-e!

Any idea?
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Old   August 7, 2013, 06:49
Default Refer to Literature
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Dear Maysam,

Kindly refer to the RSM Assessment, Disadvantages in Versteeg & Malalasekara "Introduction to CFD", where it has been mentioned.

"In some flows RSM performs just as poorly as k-epsilon model "
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Old   October 8, 2013, 02:36
Default Lrr
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I used to LRR in cyclone, so it had showed better results than k-eps both k-omega models.

I think it's a good model for special cases.
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Old   October 8, 2013, 23:28
Default LRR CASE FILE - Reg
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Dear skeptik,

Thats good to hear.

If you don`t mind, can you upload your LRR case in zipped format for reference.

I am using LRR for Jet flows and I am finding difficulty in convergence and some other problems. So it would be helpful if I go through some converged cases. By that hope I can figure out what is going wrong in my simulations.

Thanks in advance.
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Old   October 11, 2013, 16:48
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Hi maysmech,

The evaluation of the turbulence model is not that straightforward!

Mesh resolution and wall modelling strategy is quite critical for the conclusions of the simulations results. In any case, if there is no high strain in your flow, I cannot see the advantage of using a highly expensive turbulence model like RSM. For a large number of applications, the isotropic assumption is fair enough.

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Old   October 12, 2013, 17:21
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Here you can download cyclone- testcase
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Old   October 15, 2013, 01:20
Default LRR axisymmetric jet
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Dear Skeptik,
I used almost the same conditions as you used, but for axisymmetric jet case i am finding difficulties in convergence and getting physically possible solutions
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Old   October 15, 2013, 01:42
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Quote:
Originally Posted by skyinventorbt View Post
Dear Skeptik,
I used almost the same conditions as you used, but for axisymmetric jet case i am finding difficulties in convergence and getting physically possible solutions
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As i know, it's a common problem of the RSM-models.
But, possibly, bad convergence and non-physically solutions were reasoned by wrong boundary conditions. What is your case? Can you publish it?
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Old   October 18, 2013, 00:32
Default Lrr case
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Dear Skeptik,

Here is the first case which i tried.

Simulation of Axisymmetric Free Jet using LRR Reynolds Stress Model

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Old   November 7, 2013, 17:05
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Hi there skeptik,

Thank you very much for you cyclone download, I also wanted to try out LRR for a cyclone so your post was very useful.

I was wondering, did you ever manage to verify the results on your cyclone? I ran your case first with simpleFoam with no turbulence and then with LRR activated. The velocity plot in the z-plane (which Im assuming is the tangential velocity profile?) still appears to be a non Rankine Vortex like this one for K-e.
http://www.waset.org/journals/waset/v59/v59-328.pdf

Whereas I am hoping RSM/LRR looks like this one...which is good enough for what I am currently doing
http://www.cfd.com.au/cfd_conf12/PDFs/040KAR.pdf

What do you think? Any comments appreciated.

Best Regards

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Old   November 8, 2013, 01:08
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Quote:
Originally Posted by jason View Post
I was wondering, did you ever manage to verify the results on your cyclone? I ran your case first with simpleFoam with no turbulence and then with LRR activated. The velocity plot in the z-plane (which Im assuming is the tangential velocity profile?) still appears to be a non Rankine Vortex like this one for K-e.
http://www.waset.org/journals/waset/v59/v59-328.pdf

Whereas I am hoping RSM/LRR looks like this one...which is good enough for what I am currently doing
http://www.cfd.com.au/cfd_conf12/PDFs/040KAR.pdf
Hi Jason,

About my case. The velosity profile was not correct. But at least RSM results were better than k-eps. Sorry, I can't remember what was right and what was wrong exactly.

My cyclone was just a test-case, i've used third-party mesh. May be problem in initial conditions or in the mesh discretisation. At least about that case i'd say that mesh needs to be refined in near-wall region. For instance by 'refineWallLayer" function. Also as i remember there was tetra-mesh. It could be converted by polyDualMesh which reduces mesh size. Finally i didn't try to change fvSchemes.
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Old   November 8, 2013, 01:13
Default Another pic about RSM
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Here you can see differences.
Vortexes are little bit bigger and have little bit higher frequency. But not so high as in experimental case.

a10_comp2.jpg
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Old   November 8, 2013, 05:52
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Hi again,
Thanks for the reply, I'm testing a snappy mesh with layers but I think the mesh is a little too coarse in the middle for my liking. So, I will build a pure hex mesh similar to the two cited papers and begin again.
BR
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