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February 21, 2011, 08:52 

#81 
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Join Date: Oct 2010
Location: Stuttgart
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Hello FOAMers,
I need to use the current nuSGS values in a modified pisoFoam solver (heat transfer energy equation implemented) but OF tells me, that "nuSGS" entry is missing in the turbulenceModel.H file. Do I just have to include this: // Return the subgrid viscosity virtual tmp<volScalarField> nuSGS() const = 0; in the turbulenceModel.H file and compile it with "wmake"? Or is there anything else that I have to do? Best regards grandgo 

August 21, 2011, 07:55 
What should be done for Pe>2

#82  
Senior Member

Quote:
As you told UD is not suitable for LES and CD is suggested. If the simulation acts on a flow which not possible to reach Pe<2 by fining grids, what is your suggestion for fvScheme? I mean how is possible to use a central differencing scheme for Pe>2? Regards, 

August 21, 2011, 14:11 

#83  
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Alberto Passalacqua
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Quote:


August 22, 2011, 14:45 

#84  
Senior Member

Quote:
If no, when Peclet number is more than 2 in most of domain so hybrid scheme would be same as Upwind and it has diffuse results problem yet. 

August 22, 2011, 19:36 

#85 
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Alberto Passalacqua
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Assuming you are actually doing LES, and not underresolved LES, your grid size should satisfy the condition on Pe' in most of the domain. This is clearly very challenging for high Reynolds numbers, and the strategy to workaround this problem would be to use very highorder schemes. In general, in the literature it is clearly shown that upwind schemes, even of highorder, are very dissipative and not suitable for LES. In practical applications, you are often not interested in the resolving all the details exactly, so some error might be acceptable (as long as you know you have it).
The 4thorder scheme has to satisfy a similar stability condition to the secondorder one, so you are at square one :) There are a variety of "filtered" schemes, like SFCD and others which are considered "better" for LES by some user. I do not have direct experience: all the LES I did was with central schemes, because I wanted the best possible accuracy with the code in use. Best, 

August 4, 2013, 08:26 

#86 
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sqing
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Location: Dalian
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Hi foamers I find that there is no dynSmagorinsky model in my OF version(OF 2.1.1), but there is a homogeneousDynSmagorinsky model. So is the latter one a similar model with the dynSmagorinsky model? If it's not, in which OF version can I find the dynSmagorinsky model? I have calculated the case about the interaction of plane wall jets with external stream with the standard Smagorinsky + VanDrist damping function, however the result turned out no so good as I expected. Especially, the velocity is much lower than the exp in the near wall region. Is it suitable to use the dynSmagorinsky model or homogeneousDynSmagorinsky model to simulate this case? Best regards


August 4, 2013, 08:57 

#87  
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Roro Wang
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Hi,
Maybe you can try this link: http://albertopassalacqua.com/?page_id=1145 foamWang Quote:


August 4, 2013, 21:13 

#88  
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sqing
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August 15, 2013, 02:58 

#89 
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sqing
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Hi Heng Xiao
I have used the dynamic model that alberto offered in a plane wall jet case. However it didn't give a good result as I expected. I have compared the result with the exp data and RANS result. It turns out the velocity near wall is much lower than the exp data. It has a opposite result with yours. I have simulate it with good mesh and the yplus is about 0.2 at first grid. I don't know what factors may lead to this result, can anyone help me? Thanks! Regard Sunxing 

March 2, 2014, 08:47 

#90 
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Florian Ries
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Hi,
I compare the dynamic model in OpenFOAM (homoDynSmag OF 2.2.2) with the dynamic model (described in Pope respectively in C.Fureby "A comparative study of subgrid scale models in homogeneous isotropic turbulenc") and I have the some Problems in understanding. In Pope (F(.) means filtered): [1] nu_SGS = cS * delta^2 * sqrt(2 * S_ij S_ij) [2] cs = (M_ij L_ij)/(M_kl M_kl) where [3] S_ij = 0.5 (ui,j + uj,i) [4] M_ij = 2 * delta^2 * (F(sqrt(2 * S_ij S_ij) S_ij)  F(sqrt(2 * S_ij S_ij)) F(S_ij)) [5] L_ij = F(ui uj)  F(ui) F(uj) In Fureby: similar to Pope but different filtering. It should be model A2 "Dynamic coefficient algebraic eddyviscosity model (AVM)" In OF 2.2.2 (homogeneousDySmagorinsky, <.> means averaged): [6] nu_SGS = cD * delta^2 * sqrt(S_ij S_ij) [7] cD = 0.5 (<L_ij M_ij>)/(<M_kl M_kl>) [8] S_ij = D_ij = S_ij Pope [9] M_ij = delta^2 * (F(sqrt(S_kl S_kl) Sij)  4 * sqrt(<S_kl> <S_kl>) <S_ij>) [10] L_ij = F(ui uj)  F(ui) F(uj) I marked the differences of these models.  First difference is the factor 0.5 in Eq[7] in comparison to Eq[2]. This comes from the factor 2 in Eq[4]. If we put this in Eq[2] we get 0.5 (ok)  Second difference is the different filtering in M_ij. What effect does this have???? (x)  Third difference is the factor 4 in Eq[9] in comparison to Eq[4]. (x)  Fourth difference is the factor 2 in mag(S_ij). (x) In my opinion these models are different or I`m not able to bring the OFmodel in the form of pope/Furebymodel. The Problem lies in the formulation of M_ij. If it is possible, anyone can please give some advice? kind regards Florian 

March 15, 2014, 23:07 

#91  
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Peter
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Quote:


March 17, 2014, 02:42 

#92 
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Florian Ries
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Hi Sunxing and palmerlee,
pherhaps the velcoity is too small, because even in the dynamic model Cs isn't 0 at the wall. As e result of this, nusgs isn't 0 > velocity is smaller. If you use a real dynamic model check Cs at the wall. If it is far away from 0 > velocity to small. Pherhaps you should use the WALE model. see here: http://aerojet.engr.ucdavis.edu/flue...ug/node508.htm the model isn't imoplemented in OF (as far as I know). kind regards Florian 

March 17, 2014, 02:52 

#93 
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Florian Ries
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Hi Foamers,
now I have understood the implementation of homoDynSmamodel in OF. For people that are interested in it: nuSGS = cD*Delta^2*(Sij Sij)^0.5 cD = <Lij Mij>/<Mkl Mkl> <.>: means averaging over the whole domain Lij = filter(ui uj)  filter(ui) filter(uj) Mij = Delta^2 * (filter((Skl Skl)^0.5 Sij)  4*(filter(Skl) filter(Skl))^0.5 filter(Sij)) with the testfilter twice the gridfilter Delta_T = 2 * Delta Mij = Delta^2 * filter((Skl Skl)^0.5 Sij)  Delta_T^2 * (filter(Skl) filter(Skl))^0.5 filter(Sij) then it is the same model as in Pope (but oter filtering) kind regards Florian 

March 17, 2014, 21:49 

#94  
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Peter
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Quote:
Thank you for your reply! How about van Driest damping, then? Could it solve this problem. kind regards Peter 

March 18, 2014, 03:41 

#95 
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Florian Ries
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Hi Palmerlee,
van Driest damping is not a good choice for dynamic models. For static Smagorinsky you can use it. In my opinion there are two easy possibilities. WALEModel or Vreman Model. These two models are very "easy" to implement. Do you have incompressible flow?? Attached you can find the WALE model I implemented in OpenFoam. It is a first version, so pherhaps there are some mistakes in it. If you will use it, please let me know about the results. For version OF2.... you can put the files in a folder in your run folder and type wmake libso. For the simulation you have to change: 1) at the begining of the controlDict include this: libs ( "libOpenFOAM.so" "libincompressibleTurbulenceModel.so" "libincompressibleLESModels.so" "libWALELESModel.so" ); application pimpleFoam; 2) In LES Properties use this: FoamFile { version 2.0; format ascii; class dictionary; location "constant"; object LESProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // LESModel WALE; turbulence on; printCoeffs on; delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } WALECoeffs { cw 0.325; } That should work and solve your problem. kind regards Florian 

March 18, 2014, 03:44 

#96 
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Florian Ries
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ok .tar is a invalid file in this forum?????
here a zipped tar: I hope this will work 

March 18, 2014, 03:47 

#97 
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Florian Ries
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Hi,
the description in the headerfile is from SmagorinskyModel. But the imoplemented model is WALE. kind regards Florian 

March 18, 2014, 08:29 

#98  
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Peter
Join Date: Nov 2011
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Quote:
Thank you very much for the code and the description! I will dig deep in this WALE model. Yes, my case have incompressible flow. It is a jet impingement flow, which has three different flow regimes: the free jet region, the stagnation region and the wall jet region. Most LES simulations for this type of flow use the dynamic Smagorinsky model in literature. You said that van Driest damping is not a good choice for dynamic models, can you explain it to me a little, perhaps? Best regards Peter 

March 18, 2014, 10:12 

#99 
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Florian Ries
Join Date: Feb 2014
Location: Darmstadt, Germany
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Hi Peter,
usually van Driest is used to model the behaviour of nuSgs ~ y³ near the wall. The dynamic procedure of Germano do the same by changing the Smagorinskyparameter. So I would not use van Driest for dynamic models, because both do the same. The advantage of the dynamic model is, that you don't have to "guess" the Smagorinskyconstant. The model will do that for you. Important is, what model do you use?? Is it the homogeneousDynSmagorinskyModel in OF?? If yes, the constant is averaged over the whole domain. That would be bad near the wall. If you use a dynamicSmagorinsky model, how do you smooth the Smagorinskyparameter. A local smoothing can be wrong near the wall (in my opinion). Pherhaps it is better to underrelax the Smagorinskyparameter over time and than do the clipping. Or, if it is stable, do not smooth the Smagorinskyparameter. You can also do LES with wall functions loglaw, WernerWenglemodel and so on. This should be better than damping. I'm not so familar with impinging jets. I will check this topic and let you know. kind regards Florian 

March 19, 2014, 02:44 

#100  
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Peter
Join Date: Nov 2011
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Quote:
Thanks a lot for the reply! I use the dynamicSmagorinsky model from here: https://bitbucket.org/albertop/dynamicsmagorinsky The Description is: Quote:
Best regards Peter 

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