[Nek5000-users] LES-wall
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Thu Jan 1 19:48:54 CST 2015
Thanks Tanmoy for the information you provided.
I am currently working on a problem very like a flow over cylinder,
where the cylinder is located in a channel. However, there is no
span-wise homogeneity in this problem (as opposed to the flow over 2D
cylinder) due to the specific channel shape. Therefore, there is no need
to averaging in spanwise planes. Beside planar averaging, however, I
couldn't find any thing else in the dynamic SGS model of "turbchannel"
example that needs to be modified for my case, as far as I understand.
Regards,
Mohsen
On 15-01-01 07:23 PM, nek5000-users at lists.mcs.anl.gov wrote:
> 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
> <mailto: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
> <mailto: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
>> <mailto: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
>> <mailto: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
>>> <mailto: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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