[Nek5000-users] LES-wall

Thu Jan 1 18:23:11 CST 2015

Hi Mohsen,

Yes you are partially right. The eddy_viscosity routines (dynamic
Smagorinsky to be precise) used in "turbChannel.usr" is indeed specific for
channel geometries, but they can be applied to geometries having small
deviations from channels, like backward facing step, box (lid driven
cavity), flat plates with very little modification. They wont work for very
complex geometries.

It is important to note, that the spatial averaging done in
"turbChannel.usr" case is to brute-force spatial homogeneity of the
statistics in that direction. If some geometry does not have special
homogeneity in one particular direction (e.g. other than periodic boundary
conditions) we can comment out the planar average routines.

I am personally using 3D flat plate geometry.

Best Regards,
Tanmoy

On Thu, Jan 1, 2015 at 5:08 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

>  Hi Tanmoy,
>
> I looked into the "turbchannel.usr" example and it seems that the spatial
> averaging of contractions, i.e., <MijLij>, needs to be modified for other
> geometries.  I Wondered if you have been using eddy-visc() routine for
> channel geometry or some other geometries.
>
> Thanks,
> Mohsen
>
>
> On 14-12-30 11:29 AM, nek5000-users at lists.mcs.anl.gov wrote:
>
>
>  Hi Mohsen,
>
>  Yes the turbChannel case is a good point to start with. However, explicit
> filtering as LES model only works when using wall-resolved LES. My past
> experience shows, to use wall-model, one must have a good eddy-viscosity
> model, to properly emulate wall layer physics. Explicit filtering of LES,
> is way too bad in preserving the wall physics.
>
>  Sincerely,
> Tanmoy
>
>   Best Regards,
>  Tanmoy
>
> On Tue, Dec 30, 2014 at 9:07 AM, <nek5000-users at lists.mcs.anl.gov> wrote:
>
>>  Thanks Tanmoy for your suggestion.
>>
>> You are right, for a eddy viscosity type of turbulent model, the Channel
>> example is a good starting point (though, I think it should be considerably
>> modified to be used in a case with a different geometry compared to a
>> channel). But I was thinking of using sort of wall model when employing the
>> explicit filtering of velocity field as a LES model.
>>
>>  Thanks,
>> Mohsen
>>
>>  On 24-Dec-14, at 11:23 PM, <nek5000-users at lists.mcs.anl.gov> wrote:
>>
>>  Hi Mohsen,
>>
>>  For LES with near wall modelling, you have to develop your own script
>> in .usr file. There are no in-built routines except eddy_visc() in
>> turbChannel example.  If you use eddy-viscosity type of near wall models in
>> LES, you can modify the scripts and write your own eddy-viscosity routines
>> in uservp.
>>
>>  Thanks,
>> Tanmoy
>>
>>   Best Regards,
>>  Tanmoy
>>
>> On Thu, Dec 25, 2014 at 12:47 AM, <nek5000-users at lists.mcs.anl.gov>
>> wrote:
>>
>>> Hello all,
>>>
>>> I have a question regarding LES capability of Nek.
>>> I know that the explicit filtering introduced in Nek can be effective
>>> for velocity field to provide sort of eddy viscosity modeling.
>>> Nevertheless, there should be some form of modeling for the near wall
>>> regions, since it is almost infeasible to have DNS like resolution in such
>>> regions for problems with relatively high Reynolds number and large scale
>>> geometries. I have seen SFR assemblies example on the Nek web in which LES
>>> used, however, I am not sure if that was an LES with near-wall resolution
>>> or with near-wall modeling.
>>>
>>> So I was wondering if anyone has any experience of using Nek LES with
>>> near wall models, or kind of hybrid RANS-LES approaches.
>>>
>>> Thanks,
>>> Mohsen
>>>
>>>
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