LES - meaning of volScalarField k in time folders

aylalisa · May 22, 2014, 07:12

Dear Foamers,

which information provides the volScalarField k in the time folders of an converged LES?

In case of a RANS computation afak k provides the turbulent kinetic energy according to $k^{'2} = \frac{1}{2} * (u^{'2} + v^{'2} +w^{'2})$ .

Aylalisa

Sylv · May 28, 2014, 06:08

Hello Aylalisa,

the volScalarField k in a LES stands for the subgrid-scale turbulent kinectic energy $k_{sgs}$ . Pope (2006) names it "residual kinetic energy" $k_{r}$ (see p.581).

Marcel

aylalisa · May 28, 2014, 11:13

Hello Marcel,

do I receive the same result for $k_\tau$ if I extract the isotropic part of volSymmTensorField UPrime2Mean (produced by utility postChannel) --> sum of the tensor's trace components multiplied by factor $\frac{1}{2}$ ?

Does this mean that UPrime2Mean $\equiv \tau^R_{ij} \equiv \tau^r_{ij} + \frac{2}{3}k_r \delta_{ij}$ ?
$\bar{p} \equiv \bar{p} + \frac{2}{3} \rho k_\tau$ --> trace elements of the tensor (isotropic residual stress) will finally be included in the modified filtered pressure? (S.Pope (13.94), page 581)

Sorry for my question invasion, I brood for a while about this point, maybe u could help...

Aylalisa

Uyan · December 23, 2014, 17:43

Hi aylalisa,

What is the utility you used to extract isotropic part of volSymmTensorField UPrime2Mean separately from UPrime2Mean ?

aylalisa · December 29, 2014, 14:12

Hi Uyan,

I would use trace().

tensor B(1, 1, 1, 2, 2, 2, 3, 3, 3);
G = tr(B)*1/3;

That probably works for the field as well.

chrissbans · February 29, 2016, 17:40

Hi All,
I run the case for channel flow(channel395) in openFoam and I am getting values for Umean magnitude ,UPrime2mean etc. Please how do I compute for U+ and Y+. Thank you

May 22, 2014, 07:12	LES - meaning of volScalarField k in time folders	#1
aylalisa Senior Member Join Date: Nov 2012 Location: Bavaria Posts: 145 Rep Power: 13	Dear Foamers, which information provides the volScalarField k in the time folders of an converged LES? In case of a RANS computation afak k provides the turbulent kinetic energy according to $k^{'2} = \frac{1}{2} * (u^{'2} + v^{'2} +w^{'2})$ . Aylalisa

May 28, 2014, 06:08		#2
Sylv New Member Marcel Vonlanthen Join Date: Nov 2012 Location: Zurich, Switzerland Posts: 28 Rep Power: 13	Hello Aylalisa, the volScalarField k in a LES stands for the subgrid-scale turbulent kinectic energy $k_{sgs}$ . Pope (2006) names it "residual kinetic energy" $k_{r}$ (see p.581). Marcel aylalisa likes this.

February 29, 2016, 17:40	How to calculate U+ and y+	#6
chrissbans New Member Christopher Yaw Bansah Join Date: Apr 2015 Location: San Antonio Posts: 1 Rep Power: 0	Hi All, I run the case for channel flow(channel395) in openFoam and I am getting values for Umean magnitude ,UPrime2mean etc. Please how do I compute for U+ and Y+. Thank you

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May 28, 2014, 11:13		#3
aylalisa Senior Member Join Date: Nov 2012 Location: Bavaria Posts: 145 Rep Power: 13	Hello Marcel, do I receive the same result for $k_\tau$ if I extract the isotropic part of volSymmTensorField UPrime2Mean (produced by utility postChannel) --> sum of the tensor's trace components multiplied by factor $\frac{1}{2}$ ? Does this mean that UPrime2Mean $\equiv \tau^R_{ij} \equiv \tau^r_{ij} + \frac{2}{3}k_r \delta_{ij}$ ? $\bar{p} \equiv \bar{p} + \frac{2}{3} \rho k_\tau$ --> trace elements of the tensor (isotropic residual stress) will finally be included in the modified filtered pressure? (S.Pope (13.94), page 581) Sorry for my question invasion, I brood for a while about this point, maybe u could help... Aylalisa

December 23, 2014, 17:43		#4
Uyan Member Join Date: Feb 2014 Posts: 62 Rep Power: 12	Hi aylalisa, What is the utility you used to extract isotropic part of volSymmTensorField UPrime2Mean separately from UPrime2Mean ?

December 29, 2014, 14:12		#5
aylalisa Senior Member Join Date: Nov 2012 Location: Bavaria Posts: 145 Rep Power: 13	Hi Uyan, I would use trace(). tensor B(1, 1, 1, 2, 2, 2, 3, 3, 3); G = tr(B)*1/3; That probably works for the field as well.