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dynamic Smagorinsky model in OpenFOAM 3.0.1

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Old   April 12, 2016, 09:36
Default dynamic Smagorinsky model in OpenFOAM 3.0.1
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Kamil ÖZDEN
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Dear All,

As far as I investigated there is no dynamic Smagorinsky model in OpenFOAM 3.0.1. Am I right? Is it possible to use this model in OpenFOAM 3.0.1.

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Kamil
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Old   April 12, 2016, 12:44
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Mahdi Hosseinali
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The dynamic Smagorinsky in previous versions was averaging the coefficient over the whole domain (which defeats the whole purpose of a dynamic solution). However you can use the dynamicLagrangian model which is supposed to perform the averaging over a streamline.
I have posted the case files for channel395 here:
http://www.cfd-online.com/Forums/ope...s-model-2.html
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Old   April 13, 2016, 04:14
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Kamil ÖZDEN
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Hi Mahdi,

Thanks for your answer. It's very beneficial for me. I've investigated your channel flow case with DynLag and distinguished that there is a parameter (different than dynSmago) called theta under dynamicLagrangianCoeffs in turbulenceProperties file. What is the function of this parameter? How can I decide to the value of it?

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Kamil
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Old   April 15, 2016, 13:14
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Mahdi Hosseinali
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Usually it's for the best not to change a turbulence model's parameters as they have been adjusted.
But to take a deeper look into the model you can check the paper that the model has been implemented based on:
http://journals.cambridge.org/action...ine&aid=413557
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Old   April 17, 2016, 07:33
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Kamil ÖZDEN
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Hi Mahdi,

Thanks for your reply and keen interest. As a last question let me ask how to calculate (guess) the initial condition for flm and fmm parameters? For example how did you calculate 2.56e-6 for flm and 1e-4 for fmm as initial condition?

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Kamil
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Old   September 4, 2016, 12:16
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Lorenzo
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Good evening to all,

as far as I know and I experienced the initial values should be choosen so as to avoid divergence in the calculation of flm and fmm after the first steps of the simulation. Once in the run the model should not be affected significantly by them.
Please correct me if I'm wrong with this issue, I' m a newby with dynLagrangian model.

anishtain4, in the case you posted you worked on a structured grid. In my study I have an unstructured grid and I bump into divergence of flm at the initial steps, only if flm is set as initial condition at a very very small number (1e-16) the simulation goes on , but divergence soon or later occurs due to the same behaviour of flm. Do you think it has to do with the grid quality? ( cell size first of all)
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Old   October 16, 2016, 16:32
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Mirage
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Quote:
Originally Posted by Lorenzo92 View Post
Good evening to all,

as far as I know and I experienced the initial values should be choosen so as to avoid divergence in the calculation of flm and fmm after the first steps of the simulation. Once in the run the model should not be affected significantly by them.
Please correct me if I'm wrong with this issue, I' m a newby with dynLagrangian model.

anishtain4, in the case you posted you worked on a structured grid. In my study I have an unstructured grid and I bump into divergence of flm at the initial steps, only if flm is set as initial condition at a very very small number (1e-16) the simulation goes on , but divergence soon or later occurs due to the same behaviour of flm. Do you think it has to do with the grid quality? ( cell size first of all)
Hey Guys,

@Lorenzo92, did u get answers to ur questions?

@anishtain4 , Do u think that ur code can provide the same results as the dynamic Smagorinsky in OF 2.3 ?

Why did OF change the SGS model? What did they improve and change?

how can I make sure, that i can use a dynamic Smag in OF 3.01 correctly?

@Kamil did u find a solution to ur problem?
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Old   October 17, 2016, 09:45
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Hi Mirage,

1)thank for your interest in the issue first of all. Well, the answer is NOT. I think I can localize the problem however: nuSgs explodes since Cs ( Smagorinsky coefficient ) explodes in the simulation due to the innatural increase in flm (which is the double inner product Lij :: Mij according to the theory).
Moreover, the time scale used for integration of flmm is not the one suggested by the creators of the model (Meneveu et al.), I think I'll modify that time scale as a very very last effort.
Another key point is the time integration of flmm and fmm, that could cause instability. I do not remember even if these terms are handled in an implicit or explict fashion . This is to check in my view and I'll get through as soon as I can.

2)Coming to your second question maybe I can help you a little: in OF 2.4.0 (my current version) the homogeneosDynSmagorinsky model should do that.
Dynamic procedure is applied to Cs by averaging the quantities Lij::Mij and Mij::Mij over the surface of each cell despite of what is written in the header file of the model.
I checked the function fvc::average used in the model and found out that the average is performed over cell's faces not over the entire domain. Check out the code and correct me if I'm wrong.

Best regards,

Lorenzo92
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