
[Sponsors] 
February 18, 2007, 06:17 
Hi all,
is it possible to f

#1 
Member
stefan
Join Date: Mar 2009
Posts: 96
Rep Power: 10 
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. 

August 22, 2007, 09:33 
Hi guys
I am looking into LES

#2 
New Member
morteza
Join Date: Mar 2009
Posts: 18
Rep Power: 10 
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 

August 22, 2007, 10:59 
Hi merteza,
I think you can

#3 
Senior Member
Cedric DUPRAT
Join Date: Mar 2009
Location: Nantes, France
Posts: 188
Rep Power: 10 
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 LargeEddy Simulations of Turbulence) are very usefull and interresting if you plan to work on LES. good reading :) Cedric 

September 10, 2007, 04:36 
Hi all
I want to know what ki

#4 
New Member
ehsan yasari
Join Date: Mar 2009
Location: Gothenburg, Sweden
Posts: 14
Rep Power: 10 
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 

September 20, 2007, 06:02 
Source code for explicit LES f

#5 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 14 
Source code for explicit LES filters are in $FOAM_SRC/LESmodels/LESfilters
Generally, LES in OpenFOAM uses the implicit tophat filter. 

September 26, 2007, 10:34 
Hi Eugene and all
Thanks Eug

#6 
New Member
ehsan yasari
Join Date: Mar 2009
Location: Gothenburg, Sweden
Posts: 14
Rep Power: 10 
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: 1Algorithm and Formulation of filtration that used in these codes. 2According 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. 3What is "widthcoeff_" that used in these codes? We REALLY need the answer of these question.thanks for your help. 

December 5, 2010, 19:15 

#7  
Member
Join Date: Oct 2010
Location: Stuttgart
Posts: 35
Rep Power: 9 
Quote:
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 

December 15, 2010, 13:43 

#8 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 14 
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.


January 19, 2011, 04:15 
LES convergence criterea

#9 
New Member
Vitaly
Join Date: Sep 2010
Posts: 6
Rep Power: 9 
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=(0.5average(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*(0.50.5*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; } } 

January 21, 2011, 12:45 
LES Filtering

#10  
Member

Quote:
did you find the answer of these questions? I would appreciate if you could help me. Best Regards, 

April 6, 2011, 12:01 

#11 
Member
Kim Yusik
Join Date: Dec 2009
Posts: 39
Rep Power: 10 
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 

July 11, 2012, 09:57 

#12 
Senior Member
ehsan
Join Date: Mar 2009
Posts: 109
Rep Power: 10 
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 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
LES Filtering  SONAM  Main CFD Forum  4  September 17, 2008 05:18 
Filtering  Filtering  FLUENT  3  February 8, 2002 12:20 
LES> Filtering.  A. Student.  Main CFD Forum  3  December 13, 2001 12:54 
box filtering  jooks  Main CFD Forum  1  March 6, 2000 18:34 
box filtering  jooks  Main CFD Forum  0  March 3, 2000 01:30 