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-   -   Problems with the RSM in simpleFoam (http://www.cfd-online.com/Forums/openfoam-solving/60032-problems-rsm-simplefoam.html)

sberg September 1, 2006 14:59

I've tried to run some 3D simu
 
I've tried to run some 3D simulations with a Reynolds stress model lately, but they will not converge. I've played around with the settings and variables but the simulations remains unstable. However, with the k-epsilon model the simulations converges nicely. Have anyone else had succees with the RSM, or am I doing something utterly wrong?

hjasak September 1, 2006 15:19

It should work without problem
 
It should work without problems. If you are running something relatively small and simple I wouldn't mind having a look, just to make sure RSTM is still fine.

Hrv

sberg September 2, 2006 05:21

It's a small case where two sq
 
It's a small case where two square ducts, each of them with dimensions 0.1*0.1*1 (m), are joined together in a 90 degree bend. Air is flowing through at a Reynolds number of 100,000. The turbulence intensity, and the turbulent length scales compared to the outer dimensions, are both assumed to be 10 %.

The kEpsilon and RNGkEpsilon works well on this geometry, but I cannot obtain a solution with the LRR or LaunderGibsonRSTM models.



sberg September 2, 2006 05:40


 


hjasak September 2, 2006 05:48

Steve, I don't think you ma
 
Steve,

I don't think you managed to attach the file.

Hrv

newbee September 2, 2006 05:49

Hi, Im a beginner att openF
 
Hi,

Im a beginner att openFOAM but I have tried the turbmodels you mension and I have had a similar problem which i got thru by having a epsilon value 3 times as big as when I used the kepsilon models.

/erik

sberg September 2, 2006 08:15

I'll try again:-) Here is a
 
I'll try again:-)

Here is a link to the case: http://home.chello.no/~sberg/bend.tar.gz


Steve

hjasak September 2, 2006 15:02

I don't see a problem: it conv
 
I don't see a problem: it converges monotonically. This is what I did:
- run 100 iterations with k-epsilon
- calculated Reynolds stress using R
- restarted with Launder-Reece-Rodi RSTM.

Converges smoothly with no trouble. I can either give in normal stress only at the inlet of the full equilibrium R from the k-epsilon model.

A few comments:
- your numerics is rubbish: you should try using second order
- if you try to start up LRR from the beginning it blows up because of epsilon. You should really start k-epsilon and restart; otherwise you will have fun trying to set up under-relaxation coefficients
- at the end of the residual graph you start hitting solver convergence tolerances: hence the plateau
- I can make this even better using my fixedMeanValue outlet b.c.: makes it prettier close to the outlet

http://www.cfd-online.com/OpenFOAM_D...ges/1/3006.jpg

Hrv

sberg September 3, 2006 12:00

Hi Hrvoje I didn't now abou
 
Hi Hrvoje

I didn't now about the "R" function.

When I followed you steps the solution converged without problem.

Thank you

Steve

Daniele111 August 15, 2010 07:14

1 Attachment(s)
Hi
I try to use LRR for my simulation. I'm simulating an atmospheric boundary layer, but my result with it are completely different from the same case with k-eps model. Post my case.
Thanks

CHARLES February 25, 2014 20:39

Quote:

Originally Posted by hjasak (Post 188472)
A few comments:
- your numerics is rubbish: you should try using second order
Hrv

Hrvoje,
Could you please provide an fvSchemes and fvSolution that aren't "rubbish"?
I'm not very well-versed in numerical methods (yet!) and would like to get a better idea of what 'good' settings for LRR are.

Thanks!


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