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September 1, 2009, 11:34 
LowRe turbulence models

#1 
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Gavin Tabor
Join Date: Mar 2009
Posts: 181
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Hi. I'm trying to run simpleFoam using the lowRe turbulence models. I've run a preliminary calculation using the standard ke model, then switched models. Each time on startup I get the following output;
Starting time loop Time = 1001 DILUPBiCG: Solving for Ux, Initial residual = 9.45357e05, Final residual = 9.97272e08, No Iterations 2 DILUPBiCG: Solving for Uy, Initial residual = 0.0012608, Final residual = 2.48792e06, No Iterations 2 DILUPBiCG: Solving for Uz, Initial residual = 0.000676913, Final residual = 7.49901e07, No Iterations 2 DICPCG: Solving for p, Initial residual = 0.0957274, Final residual = 9.47486e07, No Iterations 318 DICPCG: Solving for p, Initial residual = 0.00598807, Final residual = 9.84517e07, No Iterations 207 time step continuity errors : sum local = 3.38296e08, global = 5.26895e10, cumulative = 5.26895e10 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*(1exp((Am*(((sqrt(k)*y)nu)+1e15)))))((1exp((Aepsilon*(((sqrt(k)*y)nu)+1e15))))+1e15))*sqr(k))(epsilon+epsilonSmall)) nu p (symm(grad(U))&&grad(U)) ((((Cmu*((1exp((Am*(((sqrt(k)*y)nu)+1e15))))((1exp((Aepsilon*(((sqrt(k)*y)nu)+1e15))))+1e15)))*sqr(k))epsilon)*(symm(grad(U))&&grad(U))) ((1exp((Am*(((sqrt(k)*y)nu)+1e15))))((1exp((Aepsilon*(((sqrt(k)*y)nu)+1e15))))+1e15)) (sqr(k)(nu*epsilon)) (((sqrt(k)*y)nu)+1e15) (((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 

September 1, 2009, 19:20 
Replace *WallFunction in k and epsilon fields

#2 
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Richard Smith
Join Date: Mar 2009
Location: Enfield, NH, USA
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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 highRe to lowRe. Something to check.
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February 15, 2010, 10:52 

#3 
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Aniko Rakai
Join Date: Oct 2009
Location: Geneva
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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 1e10; } ? 

February 15, 2010, 11:10 

#4 
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Richard Smith
Join Date: Mar 2009
Location: Enfield, NH, USA
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You have to provide meaningful epsilon and k values, for more see:
http://www.cfdonline.com/Wiki/Turbu...ary_conditions but otherwise yes. If you are not sure about the difference between highRe and lowRe turbulence models then I'd suggest sticking with highRe, i.e., turbulence models that use wall functions. Hope this helps.
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February 15, 2010, 11:25 

#5 
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Aniko Rakai
Join Date: Oct 2009
Location: Geneva
Posts: 30
Rep Power: 8 
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. 

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