CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Low-Re turbulence models

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree2Likes
  • 1 Post By grtabor
  • 1 Post By gocarts

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 1, 2009, 12:34
Default Low-Re turbulence models
  #1
Senior Member
 
Gavin Tabor
Join Date: Mar 2009
Posts: 181
Rep Power: 17
grtabor is on a distinguished road
Hi. I'm trying to run simpleFoam using the low-Re turbulence models. I've run a preliminary calculation using the standard k-e model, then switched models. Each time on startup I get the following output;

Starting time loop

Time = 1001

DILUPBiCG: Solving for Ux, Initial residual = 9.45357e-05, Final residual = 9.97272e-08, No Iterations 2
DILUPBiCG: Solving for Uy, Initial residual = 0.0012608, Final residual = 2.48792e-06, No Iterations 2
DILUPBiCG: Solving for Uz, Initial residual = 0.000676913, Final residual = 7.49901e-07, No Iterations 2
DICPCG: Solving for p, Initial residual = 0.0957274, Final residual = 9.47486e-07, No Iterations 318
DICPCG: Solving for p, Initial residual = 0.00598807, Final residual = 9.84517e-07, No Iterations 207
time step continuity errors : sum local = 3.38296e-08, global = -5.26895e-10, cumulative = -5.26895e-10



request for volScalarField RASModel::G from objectRegistry region0 failed
available objects of type volScalarField are

14
(
pPrevIter
(1-(0.3*exp(-sqr((sqr(k)|(nu*epsilon))))))
k
((((Cmu*(1-exp((-Am*(((sqrt(k)*y)|nu)+1e-15)))))|((1-exp((-Aepsilon*(((sqrt(k)*y)|nu)+1e-15))))+1e-15))*sqr(k))|(epsilon+epsilonSmall))
nu
p
(symm(grad(U))&&grad(U))
((((Cmu*((1-exp((-Am*(((sqrt(k)*y)|nu)+1e-15))))|((1-exp((-Aepsilon*(((sqrt(k)*y)|nu)+1e-15))))+1e-15)))*sqr(k))|epsilon)*(symm(grad(U))&&grad(U)))
((1-exp((-Am*(((sqrt(k)*y)|nu)+1e-15))))|((1-exp((-Aepsilon*(((sqrt(k)*y)|nu)+1e-15))))+1e-15))
(sqr(k)|(nu*epsilon))
(((sqrt(k)*y)|nu)+1e-15)
(((C2*(1-(0.3*exp(-sqr((sqr(k)|(nu*epsilon)))))))*epsilon)|k)
epsilon
y
)

followed by a stack trace. What am I doing wrong? I've tried this with both the LaunderSharmaKE and the LienLeschzinerLowRe models with the same result. From an initial inspection of the code I can't see that G is being read in (in fact I think its calculated) and its not complaining about that.

Any suggestions gratefully received.

Gavin
kingjewel1 likes this.
grtabor is offline   Reply With Quote

Old   September 1, 2009, 20:20
Default Replace *WallFunction in k and epsilon fields
  #2
Senior Member
 
gocarts's Avatar
 
Richard Smith
Join Date: Mar 2009
Location: Enfield, NH, USA
Posts: 138
Blog Entries: 4
Rep Power: 17
gocarts is on a distinguished road
I came across the same problem - but it was my fault.

I hadn't replaced the epsilonWallFunction and kqRWallFunction conditions in the epsilon and k fields (case time directory) when I switched turbulence models high-Re to low-Re. Something to check.
fumiya likes this.
__________________
Symscape, Computational Fluid Dynamics for all
gocarts is offline   Reply With Quote

Old   February 15, 2010, 10:52
Default
  #3
Member
 
Aniko Rakai
Join Date: Oct 2009
Location: Geneva
Posts: 30
Rep Power: 16
ancsa is on a distinguished road
Hi Richard,
by replacing you mean deleting it and simply adding a small value like in epsilon and k file e. g. :
SL6
{
value uniform 1e-10;
}
?
ancsa is offline   Reply With Quote

Old   February 15, 2010, 11:10
Default
  #4
Senior Member
 
gocarts's Avatar
 
Richard Smith
Join Date: Mar 2009
Location: Enfield, NH, USA
Posts: 138
Blog Entries: 4
Rep Power: 17
gocarts is on a distinguished road
You have to provide meaningful epsilon and k values, for more see:
http://www.cfd-online.com/Wiki/Turbu...ary_conditions
but otherwise yes.

If you are not sure about the difference between high-Re and low-Re turbulence models then I'd suggest sticking with high-Re, i.e., turbulence models that use wall functions.

Hope this helps.
__________________
Symscape, Computational Fluid Dynamics for all
gocarts is offline   Reply With Quote

Old   February 15, 2010, 11:25
Default
  #5
Member
 
Aniko Rakai
Join Date: Oct 2009
Location: Geneva
Posts: 30
Rep Power: 16
ancsa is on a distinguished road
Thanks for fast reply. I will try to go on as you suggested, I know how to calculate the values.
I'm calculating my eps and k profile from measurement data, only I have no points near the wall, I was using wall functions hence, I just wanted to see the difference in the results if I change and I read in the forums to use small figures but not zero. I will read more about it.
ancsa is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Turbulence model for low Reynolds number flow? Nokadu Main CFD Forum 3 May 26, 2013 12:42
Discussion: Reason of Turbulence!! Wen Long Main CFD Forum 3 May 15, 2009 10:52
Turbulence Models for very low Reynolds Numbers Sudhi CFX 1 March 2, 2007 19:03
Multicomponent fluid Andrea CFX 2 October 11, 2004 06:12


All times are GMT -4. The time now is 09:22.