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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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Old   October 8, 2023, 09:00
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Xingguang Zhou
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Hi Patil, maybe you can make the validation with Kim, Moin, and Moser (1987) DNS data for TKE production rate and dissipation rate. Nowadays, I also dedicate myself to quasi-DNS with OpenFOAM. The equations of TKE production rate and dissipate rate are both same to yours. However, I try to post-process these two physical quantities in the way to make the modification of solver and utilities, ie pisoFoam and postChannel (OpenFOAM v2006).

The case is running on HPC, and I will make the comparation with MKM (1987) to verify whether these methd is correct or not.

Best regards.

Xingguang Zhou.
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Old   April 29, 2024, 11:01
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Quote:
Originally Posted by watermelon View Post
Hi Patil, maybe you can make the validation with Kim, Moin, and Moser (1987) DNS data for TKE production rate and dissipation rate. Nowadays, I also dedicate myself to quasi-DNS with OpenFOAM. The equations of TKE production rate and dissipate rate are both same to yours. However, I try to post-process these two physical quantities in the way to make the modification of solver and utilities, ie pisoFoam and postChannel (OpenFOAM v2006).

The case is running on HPC, and I will make the comparation with MKM (1987) to verify whether these methd is correct or not.
Hi Xingguang,
I am wondering if you have got any good results and I am also quite interested in this topic. Thanks.
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Old   April 29, 2024, 11:21
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Akshay Patil
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Hi,


I stopped using OpenFOAM for simple Channel Flow type DNS since its not fast enough compared to some existing spectral and/or finite difference solvers. Initially my aim was to extend it for non-flat channel walls but it was easier to implement an immersed boundary method as opposed to using OpenFOAM. Hope this helps and sorry I cannot be of much help with regards to this.
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