TKE production and Dissipation for DNS

Akshay_11235 · March 30, 2020, 21:50

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

watermelon · October 8, 2023, 09:00

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.

March 30, 2020, 21:50	TKE production and Dissipation for DNS	#1
Akshay_11235 Member Akshay Patil Join Date: Nov 2015 Location: Pune, India Posts: 34 Rep Power: 10	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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October 8, 2023, 09:00		#2
watermelon New Member Xingguang Zhou Join Date: May 2022 Location: CHINA Posts: 13 Rep Power: 3	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.