[mxylondon]

Dear Foamers,

When I use LES model for a 2D case, it suggests that 'LES is not strictly applicable.....'
So, it means it is not ok to use LES for 2D case? A little bit confused.

[nimasam]

it can be used numerically, but when i asked an expert in turbulence it says using LES for 2D cases is non-sense as it LES using spatial filter

[flotus1]

Two-dimensional turbulence has different physical behavior than three-dimensional turbulence.
That is why LES on a 2-dim. domain should not be used to obtain reliable results for 3-dim. flows.

[mxylondon]

Emmm, I am using a 2D case to test my own developed solver, coz 3D case is bloody time-waste, if put too many grid inside the layer Y+<30.
I mean, is it a possible way to confirm the LES model's working well?

[flotus1]

If you are comparing your results to the results from another 2D LES solver, you should be fine.

[Lieven]

Hi Xiangyin,


Both Alex and Nima are correct. You need to make a distinction between validating your implementation and validating your model.
* If you purely want to validate your solver (so the numerical implementation), you can compare your results with other solvers.
* However, if you want to validate it, doing a 2D LES is basically pure non-sense. Turbulence is by definition a 3D effect. As soons as you neglect this, you will probably end up with pure rubbish.

Cheers,

Lieven

[mxylondon]

Thank you guys! That's really what I want to know.
My plan is to make sure every step is OK before using real 3D running, otherwise it is too long to try something in setup.
Thanks again!

[amuzeshi]

Originally Posted by Lieven

Hi Xiangyin,


Both Alex and Nima are correct. You need to make a distinction between validating your implementation and validating your model....

Lieven

Hi,
Why OpenFOAM contains 2D pitzDaily with LES in

tutorials/incompressible/pisoFoam/LES/pitaDaily

?
Obviously it does not need to validate implementation, on the other hand, based on your saying, it is completely rubbish!
Then why?

[HPE]

OpenFOAM tutorials are neither validation nor verification, but only a set of illustrations of the functionalities of OpenFOAM, so that users can fetch parts useful to them.

[amuzeshi]

Originally Posted by HPE

OpenFOAM tutorials are neither validation nor verification, but only a set of illustrations of the functionalities of OpenFOAM, so that users can fetch parts useful to them.

By the way, I don't think they put a wrong case just for illustration purposes; Existing a 2D LES case somehow depicts the allowability of using LES with 2D geometries, at least in some situations.

[HPE]

turbulence is by definition a three-dimensional phenomenon, except for some simplified cases of atmospheric flows; therefore, 2D LES is almost always nonsense since any vortex stretching mechanism is theoretically nonexistent in the governing equations (note: I do not refer to statistically independency or homogeneity). accordingly, they have definitely put the tutorial as an illustration, in my opinion.

[Zahra99]

Hi
Your guids and helps are so good, I use them
Thank you very much.