[Nek5000-users] Number of Elements per Characteristic Length for DNS

[nek5000-users at lists.mcs.anl.gov]

Hello Philipp,

Thanks again for getting back to me and for sending these references.

Regards,

Tommy

On Thu, Jul 12, 2018 at 9:07 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> I guess the El Khoury paper might be a good starting point; we really
> tried to make sure that the resolution is sufficient for good DNS.
> Otherwise, there is a resolution discussion for spectral methods in the
> paper by Coleman, Johnstone and Spalart:
>
> https://aip.scitation.org/doi/abs/10.1063/1.3247176
>
> Philipp
>
> On 2018-07-12 14:56, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Hi Philipp,
>>
>> Thank you for getting back to me. Do you have any references that you
>> could provide so that I can look into this further?
>>
>> Thanks,
>>
>> Tommy
>>
>> On Thu, Jul 12, 2018 at 4:25 AM, <nek5000-users at lists.mcs.anl.gov
>> <mailto:nek5000-users at lists.mcs.anl.gov>> wrote:
>>
>>     Hi,
>>     typically, in wall bounded turbulence you would design the mesh
>>     based on inner scaled quantities (i.e. based on the viscous length
>>     scale l*). This is what we have done in the paper by El Khoury, in
>>     accordance to studies in channel flow. TOwards the centre, one can
>>     then also use Kolmogorov units (not sure whether Taylor units are so
>>     useful). I am quite convinced that the El Khoury simulations are
>>     well-resolved DNS, which can also be seen when looking at spectra.
>>
>>     Philipp
>>
>>
>>     On 2018-07-11 20:58, nek5000-users at lists.mcs.anl.gov
>>     <mailto:nek5000-users at lists.mcs.anl.gov> wrote:
>>
>>         Hello All,
>>
>>         I am currently investigating the turbulence in a pipe with
>>         periodic boundary conditions. I am working on building my mesh
>>         and was planning on using Re^(3/4) as the number of elements per
>>         characteristic length, but I have found differing methods in
>>         literature detailing the number of elements used for DNS. One
>>         paper in particular (G.K. El Khoury et al, Direct Numerical
>>         Simulation of Turbulent Pipe Flow at Moderately High Reynolds
>>         Numbers,  Flow Turbulence Combust, 2013) uses Nek5000 to
>>         simulate turbulent flow in a pipe at different Reynolds numbers.
>>         The number of elements calculated in this paper seem to be in
>>         between the LES and DNS suggested number of elements (element
>>         size between the Taylor microscale and the Kolmogorov scale).
>>         Turbulent Flows by Pope however suggests a number of elements
>>         that is slightly larger than Re^(3/4), and is dependent on the
>>         Taylor microscale Reynolds number.
>>
>>         Any suggestions on the correct way to determine the number of
>>         spectral elements in a characteristic length would be appreciated.
>>
>>         Regards,
>>
>>         Tommy
>>
>>
>>
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