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-   -   LES filtering (http://www.cfd-online.com/Forums/openfoam-solving/59416-les-filtering.html)

stefanke February 18, 2007 06:17

Hi all, is it possible to f
 
Hi all,

is it possible to filter the governing equations only in two directions? I want to filter the equations only in the streamwise and spanwise direction in a channel flow simulation. Any hints or comments are really appreciated.

morteza August 22, 2007 09:33

Hi guys I am looking into LES
 
Hi guys
I am looking into LES filters codes e.g. laplacian, simple,etc but it looks strange to me.
Can someone tell me about the main equations for these filters(or refrences).

thanks in advance
Morteza

cedric_duprat August 22, 2007 10:59

Hi merteza, I think you can
 
Hi merteza,
I think you can have a look on one turbulence book, there is always a part which explain filtering.
I don't know which one is your favorite one but those from M. Lesieur (Turbulence in fluid and Large-Eddy Simulations of Turbulence) are very usefull and interresting if you plan to work on LES.

good reading :-)

Cedric

ehsanyasari September 10, 2007 04:36

Hi all I want to know what ki
 
Hi all
I want to know what kind of filter used in OpenFoam (explicit or implicit) and how can i find the source code of them.
Any hints or comments are really appreciated.

Sincerely,

Ehsan

eugene September 20, 2007 06:02

Source code for explicit LES f
 
Source code for explicit LES filters are in $FOAM_SRC/LESmodels/LESfilters

Generally, LES in OpenFOAM uses the implicit tophat filter.

ehsanyasari September 26, 2007 10:34

Hi Eugene and all Thanks Eug
 
Hi Eugene and all
Thanks Eugene.
Our thease is about filtration in LES.
We study LESfilters codes (LESfilter,NewFilter,Simple,Laplace,anistropic) but we have following problem about them:
1-Algorithm and Formulation of filtration that used in these codes.
2-According to the discription part of laplacefilter.H and anisotropicfilter.H :

Description
Kernel as filter as Test filter with ratio 2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
Box filter: g = delta2/24 -> g = delta2/6
Spherical box filter: g = delta2/64 -> g = delta2/16
Gaussian filter: g = delta2/24 -> g = delta2/6

what is "g" parameter and where is the effect of "g" in these codes.
3-What is "widthcoeff_" that used in these codes?

We REALLY need the answer of these question.thanks for your help.

grandgo December 5, 2010 19:15

Quote:

Originally Posted by eugene (Post 180615)
Source code for explicit LES filters are in $FOAM_SRC/LESmodels/LESfilters

Generally, LES in OpenFOAM uses the implicit tophat filter.

hi eugene,

what do you mean with "generally"?

does it mean, that, if i dont choose a certain filter, OF will choose the implicit tophat filter as default?

and which one of these filters:

anisotropicFilter
laplaceFilter
LESFilter
simpleFilter

is the implicit tophat filter?

best regards

eugene December 15, 2010 13:43

The filters in FOAM are used only for dynamic SGS models to define the test filter. For the "base" filter the code always uses an implicit tophat, i.e. no filter at all. The lack of commutative filters is an issue in some classes of LES flows with rapidly changing mesh sizes.

vitvit January 19, 2011 04:15

LES- convergence criterea
 
Hello,
I'm ran several simulations of compressible JET M=0.9 Re=6e4 .
I was wondering about some stuff:
1. I'm comparing the results to some papers and I see different domain sizes - 5D in r direction and 10D in x direction. other papers use 8D in r and 30D in x - whats more correct?
2. what Bc should i use - it is an isothermal jet - I'm adding the files - are they correct?
3.in LES simulation, does watching the residuals give me something or not - Im plotting them and after a while they stay the same- good or bad - can residuals say anything about convergence in LES? Until now Im watching the U in several places for the run of the simulation using probe. but the results are confusing.
4. do I have to include sponge zone at the end of my mesh?
5. my Pe=20000 - is very high - is it a problem- I dont want a very fine mesh for now.


my Files:
T:
--------------
imensions [0 0 0 1 0 0 0];

internalField uniform 298;

boundaryField
{
inl1
{
type fixedValue;
value uniform 298;
}

out
{
type zeroGradient;
}

inl2
{
type fixedValue;
value uniform 298;
}

side
{
type totalTemperature;
value uniform 298;
T0 uniform 298;
U U;
phi phi;
rho none;
psi psi;
gamma 1.4;

}


}



U
-----------

internalField uniform (0 0 0);

boundaryField
{
inl1
{
type groovyBC;
variables "random_var=(0.5-average(rand()))*33;An=(0.04+random_var*0.0001);St =0.4+random_var*0.00085;phi=pi/3+random_var*0.00085;psi=pi/4+random_var*0.00085;theta=atan(pos().y/pos ().x);u_0=311.4;r_0=0.0016;r=pow(pow(pos().x,2)+po w(pos().y,2),0.5);del1=2*An*cos(St*u_0*time()/(2*r_0)+phi)*cos(1*theta+psi);del2=2*An*cos(St*u_0 *time()/(2*r_0)+phi)*cos(2*theta+psi);del3=2*An*cos(St*u_0 *time()/(2*r_0)+phi)*cos(3*theta+psi);del=20+del1+del2+del 3;u_new=u_0*(0.5-0.5*tanh(del*((r/r_0)-(r_0/r))));";
valueExpression "vector(0,0,u_new)";
value uniform (0 0 311.4);
}


out
{
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}

inl2
{
type fixedValue;
value uniform (0 0 0);
}

side
{
//type zeroGradient;
type inletOutlet;
inletValue uniform (0 0 0);
value uniform (0 0 0);
}


}

// ************************************************** *********************** //



P
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [1 -1 -2 0 0 0 0];

internalField uniform 101325;

boundaryField
{

inl1
{
type fixedValue;
value uniform 101325;
}


inl2
{
type zeroGradient;
}


out
{
type waveTransmissive;
field p;
phi phi;
rho rho;
psi psi;
gamma 1.4;
fieldInf 101325;
lInf 0.05;
value uniform 101325;
}



side
{
type waveTransmissive;
field p;
phi phi;
rho rho;
psi psi;
gamma 1.4;
fieldInf 101325;
//lInf 0.012;
lInf 0.05;
value uniform 101325;
}


}

yashar.afarin January 21, 2011 12:45

LES Filtering
 
Quote:

Originally Posted by ehsanyasari (Post 180616)
Hi Eugene and all
Thanks Eugene.
Our thease is about filtration in LES.
We study LESfilters codes (LESfilter,NewFilter,Simple,Laplace,anistropic) but we have following problem about them:
1-Algorithm and Formulation of filtration that used in these codes.
2-According to the discription part of laplacefilter.H and anisotropicfilter.H :

Description
Kernel as filter as Test filter with ratio 2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
Box filter: g = delta2/24 -> g = delta2/6
Spherical box filter: g = delta2/64 -> g = delta2/16
Gaussian filter: g = delta2/24 -> g = delta2/6

what is "g" parameter and where is the effect of "g" in these codes.
3-What is "widthcoeff_" that used in these codes?

We REALLY need the answer of these question.thanks for your help.

Hi Ehsan,

did you find the answer of these questions?
I would appreciate if you could help me.

Best Regards,

impecca April 6, 2011 12:01

I am trying to give little help here (and also have questions) and I can be wrong. So please do correct me if I am.

The laplace filter seems to based on one of differential filters (Ch 2.1.4 Large eddy simulation for imcompressible flow, P. Sagaut, 3rd Ed).
Helmholtz elliptic filter is same as the code in OF based on the code.
and The g is the convolution kernel but I donot know why the number 24, 64, 24 is correspond to top hat, sphirical box and gaussian filter.

And to use laplace filter as test filter, I thought I need to use large delta comparing to cubeRootVolume. so I used 0.25 as widthCoeffs (which is correpond to 'test filter delta' = 2*cubeRootVolume based on the code but it seems always diverges in a plane channel case. I tried other widthCoeffs values but no difference.

So is there anyone to manage to use laplace filter either dynSmagorinsky or mixedSmagorinsky model, please let me know.

Lastly, about the simple filter. based on the code it seems to integrate cell surfaces to filter the filed. Then is it identical to unfiltered (resolved) fileds? since OF use the finite volume method.
Thanks

Yusik

ehsan July 11, 2012 09:57

Dear all

Just asking how we could set any type of LES filter for solvers inside interPhaseChangeFoam category? By default, it uses implicit LES filters.

Regards


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