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How to calculate dissipation rate in OpenFOAM 

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November 3, 2021, 15:35 
How to calculate dissipation rate in OpenFOAM

#1 
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Farzad Faraji
Join Date: Nov 2019
Posts: 127
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Hello all
I hope you are well. I want to calculate dissipation rate in LES simulation and I find a good code for calculating TKE budget. https://github.com/AndreaDesan/pimpleTKEBudgetFoam But I can not use it since some definitions are different, so I decided to use the definitions in the code(tkeBudget.H); https://github.com/AndreaDesan/pimpl...er/tkeBudget.H Code:
volScalarField kSGS = turbulence>k(); //Instantaneous subgridscale tke volScalarField kRes = 0.5*(UPrime & UPrime); //Instantaneous resolved tke kTot = kRes + kSGS; volScalarField epsilonSGS = turbulence>epsilon(); volSymmTensorField SRes = symm(fvc::grad(UPrime)); //Instantaneous resolved fluctuating rate of strain volScalarField epsilonRes=2*nuLam*(SRes && SRes); //Instantaneous resolved dissipation rate epsilonTot = mag(epsilonRes + epsilonSGS); LESResIndex = kRes/max(kSmall,kTot); //Instantaneous ratio of resolved to total (Resolved + SGS) tke a) The dimension of tke is [m2s(2)] and "tke rate" must be [m2s(3)] b) the dimension of dissipation rate must be the same, so I calculate for both epsilonSGS and epsilonRes as below; 1 epsilonSGS = Ce*pow(k,3/2)/delta====>[Ce]*[k^3/2]/[delta]====>[1]*[m3s(3)]/[m]====>m2s(3) 2 epsilonRes = nu * (gradU && gradU)====>[m2s(1)]*[?????]=== I calculate "gradU && gradU" in OpenFoam and dimension was s(2), so we have [m2s(1)]*[s(2)]=m2s(3). basically epsilonSGS and epsilonRes has the same dimension m2s(3) which is the same as tke rate m2s(3). From this I think I have calculated the [?????] correctly. Am I correct? 

November 3, 2021, 16:28 

#2  
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Farzad Faraji
Join Date: Nov 2019
Posts: 127
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Maybe this question is a little stupid one. I always read and heard dissipation rate [m2s(3)], but I never heard about TKE rate. TKE is [m2s(2)], so TKE rate must be [m2s(3)] which is the same as dissipation rate. am I correct?
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November 8, 2021, 07:27 

#3 
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Andrea
Join Date: Feb 2012
Location: Leeds, UK
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Not sure from where within code you got "tke rate".
Andrea 

January 11, 2022, 03:44 

#4  
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Josh Williams
Join Date: Feb 2021
Location: Scotland
Posts: 71
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Quote:
You use UPrime to calculate epsilonRes, but from equation 14 in this paper [1], it appears this would give you epsilonSGS. Instead, based on [1], you should use epsilonRes_ij = nu * (gradU & gradU). Then you can probably get it as a scalar as you appear to have it by taking the trace? I have also seen epsilonRes been calculated as epsilonRes = dkRes/dt [2]. [1] Wacławczyk, M., Pozorski, J. and Minier, J.P., 2004. Probability density function computation of turbulent flows with a new nearwall model. Physics of Fluids, 16(5), pp.14101422. [2] Jayaram, R., Jie, Y., Zhao, L. and Andersson, H.I., 2020. Clustering of inertial spheres in evolving Taylor–Green vortex flow. Physics of Fluids, 32(4), p.043306. 

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dissipation rate, les, tke les 
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