# Howto get the production and dissipation of TKE??

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 June 27, 2009, 04:44 Howto get the production and dissipation of TKE?? #1 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Sponsored Links Anyone knows how to get the production and dissipation of TKE (turbulence kinetic energy)? Thanks Is it in this way: Code:  volSymmTensorField D = symm(fvc::grad(U)); //volTensorField Dprim = symm(fvc::grad(U - UMean)); volScalarField prod = -((U - UMean)*(U - UMean)) && D; volScalarField epsilon = sgsModel->epsilon(); ---------------------------------------------- Rate of production of turbulence kinetic energy from the mean flow(gradient): Rate of dissipation of turbulence kinetic energy per unit mass due to viscous stresses: __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email Last edited by lakeat; June 28, 2009 at 06:14.

 July 6, 2010, 10:55 Production and dissipation of TKE #2 New Member   Join Date: Mar 2010 Posts: 6 Rep Power: 9 Dear Daniel I am also interested in this topic. Therefore, I would like to know if you found an answer to your question in the meantime. Cheers, Irina

 July 6, 2010, 11:26 #3 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: Beijing, China Posts: 689 Blog Entries: 9 Rep Power: 14 Sorry, it'e been a long time, but doesn't the codes in my last post work for you? you can try with a channel case and see if its distribution is correct. Bye __________________ ~ Daniel WEI ------------- Boeing Research & Technology - China Beijing, China Email

 December 13, 2010, 18:51 #4 Senior Member   John Deas Join Date: Mar 2009 Posts: 160 Rep Power: 10 Hi, why did you take the symmetrical part of grad(U) ? Why didn't you compute Code: R && fvc::grad(Umean) ? Regards, JD

 December 14, 2010, 04:55 #5 Senior Member   Alberto Passalacqua Join Date: Mar 2009 Location: Ames, Iowa, United States Posts: 1,910 Rep Power: 28 Notice that the method epsilon() returns the SGS dissipation rate. Check doxygen to see how it is computed, depending on the specific model. __________________ Alberto Passalacqua GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats. OpenQBMM - An open-source implementation of quadrature-based moment methods. To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 December 14, 2010, 09:18 #6 Senior Member   John Deas Join Date: Mar 2009 Posts: 160 Rep Power: 10 Hi Alberto, thank you for your answer. When I take a look at src\turbulenceModels\LES\incompressible\oneEqEddy\ oneEqEddy.C, I read: Code: void oneEqEddy::correct(const tmp& gradU) { GenEddyVisc::correct(gradU); volScalarField G = 2.0*nuSgs_*magSqr(symm(gradU)); solve ( fvm::ddt(k_) + fvm::div(phi(), k_) - fvm::laplacian(DkEff(), k_) == G - fvm::Sp(ce_*sqrt(k_)/delta(), k_) ); bound(k_, k0()); nuSgs_ = ck_*sqrt(k_)*delta(); nuSgs_.correctBoundaryConditions(); } it appears that, in src\turbulenceModels\LES\incompressible\GenEddyVis c\GenEddyVisc.H (for example), epsilon() represents Code: ce_*sqrt(k_)/delta() . But, what I am interrested in is G, the production. Since I am doing DNS computations, I have access to both the Reynolds Stress and the gradient of the mean component of velocity, and I do not want to use any eddy viscosity to compute it, like in Code: 2.0*nuSgs_*magSqr(symm(gradU)) . I just need the formula to combine R and fvc::grad(Umean) properly. I also do not understand why the symmetric part of the gradient of U is mentionned in the previous post. Regards, JD

 December 14, 2010, 10:34 #7 Senior Member   David Boger Join Date: Mar 2009 Location: Penn State Applied Research Laboratory Posts: 146 Rep Power: 10 The double-inner product of a symmetric and asymmetric second-rank tensor is zero, so in that sense, only the symmetric part of gradU "survives" anyway. So using only the symmetric part is harmless, but perhaps unnecessary. __________________ David A. Boger

December 14, 2010, 12:21
#8
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Alberto Passalacqua
Join Date: Mar 2009
Location: Ames, Iowa, United States
Posts: 1,910
Rep Power: 28
Quote:
 Originally Posted by johndeas Hi Alberto, thank you for your answer. When I take a look at src\turbulenceModels\LES\incompressible\oneEqEddy\ oneEqEddy.C, I read: Code: void oneEqEddy::correct(const tmp& gradU) { GenEddyVisc::correct(gradU); volScalarField G = 2.0*nuSgs_*magSqr(symm(gradU)); solve ( fvm::ddt(k_) + fvm::div(phi(), k_) - fvm::laplacian(DkEff(), k_) == G - fvm::Sp(ce_*sqrt(k_)/delta(), k_) ); bound(k_, k0()); nuSgs_ = ck_*sqrt(k_)*delta(); nuSgs_.correctBoundaryConditions(); } it appears that, in src\turbulenceModels\LES\incompressible\GenEddyVis c\GenEddyVisc.H (for example), epsilon() represents Code: ce_*sqrt(k_)/delta() . But, what I am interrested in is G, the production.
My comment was to point out that

volScalarField epsilon = sgsModel->epsilon();

does not return what you want. That epsilon is only the SGS epsilon.

Since you do DNS, just apply the definition and you will be fine :-)

Best,
__________________
Alberto Passalacqua

GeekoCFD - A free distribution based on openSUSE 64 bit with CFD tools, including OpenFOAM. Available as in both physical and virtual formats.
OpenQBMM - An open-source implementation of quadrature-based moment methods.

To obtain more accurate answers, please specify the version of OpenFOAM you are using.

 July 9, 2016, 04:56 #9 Senior Member   Ehsan Asgari Join Date: Apr 2010 Posts: 311 Rep Power: 10 Hi, This is an old thread, but I wonder if anyone has achieved a reliable method to calculate TKE dissipation?! Regards

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