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March 5, 2017, 02:16 
reactingFoam abou Source trem and transport

#61 
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Wahahawsw
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I have same problem with the reactingFoam. As i have implemented my thermophysicalModel.
I have a few problems as following : 1： In the UEqn.H, how is turbulence>divDevRhoReff() calculated in the code? 2： In the EEqn.H, how is turbulence>alphaEff() and reaction>Sh() calculated in the code? 3： In the YEqn.H, how is turbulence>muEff() and reaction>R(Yi) calculated in the code? As i can't find their code, I am troubled by these problems. I want to know how these terms are calculated . Thank you very much in advance if you have some ideas about those problems. 

March 5, 2017, 03:14 

#62 
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Elyas_Kermani
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hi
first , could you tell me about your turbulence model? or LESProperties? 

March 7, 2017, 02:14 

#63 
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Emeline Noel
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Hi,
I use qtcreator in order to explore the code, you would be able to find source code for each piece. On your OpenFoam folder type qmake project *, this would create a .pro file to be open with qtcreator. It depend on the version of OF you have, for 4.x the turbulence model are in src folder under turbulenceModel folder, for you that would be the compressible subfolder. I am in holidays and don't have access to the code, it is only by memory, so scuse me if there are some mistake. Zarox 

March 8, 2017, 09:02 
div

#64  
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Wahahawsw
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Quote:
Now, I get some answer from the code. My views are as follows: 1, turbulence>divDevRhoReff() is consisted with two terms: nut()+nu(); 2, turbulence>muEff() is consisted with mut()+mu() 3, The reaction>R(Yi) could be found in the chemistrModel.So is the reaction>Sh() Did I get mistake with those ? Now I get confused with the term of alphaEff(). In some conference, alphaEff()=laminar flow alpha +turbulence alpha As some foams use alphaEff(), while some foams use turbulence>alphaEff(). what's the difference between alhaEff() and turbulencealphaEff() ? Thank you ver much if you get some idea about this question! 

May 24, 2017, 13:39 

#65 
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Elyas_Kermani
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Hello
I simulated a channel with (2pi,2,pi) and Re_tau=590 to evaluate dynamic smagorinsky model in two modes First I used the original coding in the OpenFOAM, i.e., the divDevReff with the same definition in openFOAM library as follows; tmp<fvVectorMatrix> GenEddyVisc::divDevReff(volVectorField& U) const { Return (  fvm::laplacian(nuEff(), U)  fvc::div(nuEff()*dev(T(fvc::grad(U)))) ); } In the second case, I’ve removed the dev(T(fvc::grad(U))) and replaced that with T(fvc::grad(U)). I have attached my U+ plot in two cases and DNS data. The results show a little difference. I would like to know 1Why openFOAM uses dev(T(fvc::grad(U))) instead of T(fvc::grad(U))? 2Could you say this term is used only for stability? and will have no effect on the accuracy of results? 3Why the accuracy of the simulation doesn’t acceptable in both cases using DS? I think the dynamicSmagorinsky model must be the most precise one among all the eddyviscosity models. Last edited by Elyas_Mosibat; May 25, 2017 at 01:58. 

May 29, 2017, 04:45 

#66 
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Emeline Noel
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Hi Elyas,
For incompressible flow divergence of the stress tensor is only the Laplacian of the velocity, for Stoke hypothesis with Newtonian fluids The fvc::div(nuEff()*dev(T(fvc::grad(U)))) term add to the divergence of the stress tensor a part that depend on the divergence of the velocity: for dev function for dev2 function, leading to the same formula between compressible and incompressible flow My answers : 1 Switch dev of the transpose gradient with the transpose gradient give : instead of : 2 I don't know why OpenFOAM use this additional term, even if I understood that in the new formulation it is convenient for the standardization of turbulence model structure between compressible and incompressible flow. As your test is showing, the changed of the term even if it would be theoretically zero is not in the numerical framework and so difference arise. 3 to take into account wall effect on the decrease of the turbulence for LES, I think the WALE is more suitable. Smagorinsky model family use the strain rate tensor, but the eddy of turbulence decay can't be only represent by the strain tensor, strain arise near wall that is not due to turbulence. That is the point of the WALE model to add the rotational rate tensor. By the way thank you for your contribution, now I think we have a hint that the "stabilization" term have an effect on the solution. 

January 25, 2018, 06:39 

#67  
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Hagen
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Quote:
Thank you Gerald for the very nice explanation. Nevertheless, there is still something that confuses me: So we have a modified pressure = pressure + isotropic part of Reynolds/subgrid stress tensor If I now measure a static pressure in an experiment, what do I need to do to compare my pressure to? For incompressible case I have to correct with the density of course, but do I also need to remove the isotropic stresses from the pressure? If so, how to get to those values? I think the Reynolds stresses can be extracted from the turbulent kinetic energy k, but in case of LES? Thank you very much in advance! Greets Christina 

January 25, 2018, 06:57 

#68 
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Tobias Holzmann
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Dear Christina,
I would like to refer to https://holzmanncfd.de/publications...sandopenfoam page 90.
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January 25, 2018, 07:35 

#69 
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Hagen
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Dear Tobi,
thank you for your reply. On page 91/92 I found: "Note: If we solve the incompressible ReynoldsAveraged NavierStokes equations, we are not calculating the real pressure field p. Instead we have the modied pressure p. For most of the problems this is not a big deal and we do not have to consider this. Only if we are using some modified equations in OpenFOAM where we need the real pressure, we have to recalculate the real pressure field by subtracting the kinetic part." So as I want a real pressure, the answer is yes, I have to remove the kinetic part? On page 90 I found the pressure is modified by 2/3*rho*k for Reynolds stresses. And in case of LES? Thank you again. Greets Christina 

January 25, 2018, 08:17 

#70 
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Tobias Holzmann
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I am not into the turbulence modeling but as far as I understood, the LES approach just approximates the turbulent viscosity differently. The eddyviscosity hypothesis still holds and thus, the pressure is modified. However, I would imagine that the term:
is not really big, at least not for air. Nevertheless, it is my personal derivation based on the literature I was reading. I could be also wrong. I am just a student.
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December 19, 2018, 12:00 

#71  
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Guilherme
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Hi,
I wanted to ask a question with the most experienced... I am conducting a study of DRAG REDUCTION and consequently, a new term appears in the Navier Stokes equation responsible for the polymeric stress. I could insert it into the equation using this form: Quote:
I tried to create a class just for him... Quote:
Thx 

April 22, 2019, 22:29 

#72 
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Yan Zhang
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Quote:
Thanks for your fantastic derivations! I found that in RANS, the modified pressure is p + 2/3 rho k. And in LES, the modified pressure is p  2/3 rho k. To use the absolute pressure, maybe we can overwrite the function overwrite the divDevRhoReff in a modified turbulence model, and include the twoThirdRhoK therm. Is this right? The twoThirdRhoK term is easy to add, why people don't do this?
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October 27, 2019, 11:15 

#73  
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David Long
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Quote:
Why we use fvc::div(...) here rather than fvm::div(...)? does the fvc term go to RHS of [A][x]=[b] automatically? Or it is just matrix subtraction between square matrix and column matrix: M_laplacian (n x n)  M_fvcdiv (n x 1)? Last edited by keepfit; October 29, 2019 at 04:21. 

October 27, 2019, 17:43 

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David Long
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October 27, 2019, 18:15 

#76 
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Tobias Holzmann
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Got it, ... good question. Should be as you said. The explicit guy should go to the RHS (to the source). However, I would have to investigate into that here in more detail. As you said: Matrix  Vector. But with fvc and fvm it should be done in a correct way.
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October 29, 2019, 10:06 

#77  
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David Long
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Quote:
Can you also give some explanation of the following equation for viscous force (incompressible flow, Henrik Rusche's PhD thesis P156), especially the expansion: div[mu*T(grad(u))] = grad(U) & grad(mu) + mu*grad[div(U)] 

October 29, 2019, 12:33 

#78 
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Tobias Holzmann
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Hi,
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January 11, 2020, 16:11 
Some questions about divDevRhoReff

#79 
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Saddam Hijazi
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I have question regarding the divDevRhoReff for the turbulent incompressible case


January 11, 2020, 16:13 

#80 
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Saddam Hijazi
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Quote:
Hi Tobi, thank you for you answer, I would like to clarify some doubts that I have, in this part that I quoted from your previous reply, you say that is the dynamic viscosity is constant. I suppose that you assume laminar setting otherwise, and the second term is not constant and therefore can't be taken outside the divergence operator. Secondly, why you wrote the second term the following way ? should not be written like this ? Thank you very much. 

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