# Low-Re turbulence models

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 September 1, 2009, 11:34 Low-Re turbulence models #1 Senior Member   Gavin Tabor Join Date: Mar 2009 Posts: 181 Rep Power: 10 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.

 September 1, 2009, 19:20 Replace *WallFunction in k and epsilon fields #2 Senior Member     Richard Smith Join Date: Mar 2009 Location: Enfield, NH, USA Posts: 138 Blog Entries: 4 Rep Power: 10 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

 February 15, 2010, 10:52 #3 Member   Aniko Rakai Join Date: Oct 2009 Location: Geneva Posts: 30 Rep Power: 10 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; } ?

 February 15, 2010, 11:10 #4 Senior Member     Richard Smith Join Date: Mar 2009 Location: Enfield, NH, USA Posts: 138 Blog Entries: 4 Rep Power: 10 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

 February 15, 2010, 11:25 #5 Member   Aniko Rakai Join Date: Oct 2009 Location: Geneva Posts: 30 Rep Power: 10 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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