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TKE production and Dissipation for DNS

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Old   March 30, 2020, 21:50
Default TKE production and Dissipation for DNS
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Akshay Patil
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Hi guys,

I am working on a DNS calculation and would like to confirm if the TKE production and Dissipation calculations on the fly make sense. I am constantly getting about one order of magnitude difference between production term and dissipation term.

in my code Production is defined as (Production = -ui'uj'dui/dxj)


Code:
volSymmTensorField gradU = symm(fvc::grad(U));
volScalarField prod = -((U - u_bar)*(U - u_bar)) && gradU;
//Take the volume average in the domain
dimensionedScalar production = average(prod);
and Dissipation is defined as (Dissipation = nu du'i/dxj du'i/dxj)

Code:
volTensorField gradUprime = fvc::grad(U-u_bar);
volScalarField eps = nu*(gradUprime && gradUprime);
//Take the volume average in the domain
dimensionedScalar dissipation = average(eps);


When I do this the TKE production < dissipation by about an order of magnitude. I have checked the dependence of the mesh on this and it is consistently the same so I am wondering if I did something wrong here.

I am using C-N for the viscous temporal discretisation while all other settings are second order. I have also switched off the extra phi term in the Piso algorithm which stabilises the solver. Would be grateful to hear what you think. Thanks!

Regards,

Akshay Patil
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