[Nek5000-users] 3-D Taylor-Green problem

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

Hello Ammar

The filter refers to a stabilization technique and is not related to LES.
It is explained here

 "Filter-Based Stabilization of Spectral Element Methods"
<http://www-unix.mcs.anl.gov/~fischer/pubhtml/filter01.pdf>

I do not know the details of the spectral simulation. I took the data from
the website I mentioned in my post and some explanation is given in the
case description I linked to before.

I used 14^3 and 28^3 elements but within each element the velocity is a Q_9
function and pressure is Q_7 function.

Thanks for the reference. I have not seen it before and will check it out.

Thanks
praveen

On Sun, Dec 9, 2012 at 2:42 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Can you elaborate on the 512^3 case? it is impressive you are getting
> close with 32^3 and some filtering
> I was wondering :
> (1) what if you turn off filtering with 32^3  (i.e. set f=0), the question
> here if filtering is significantly contributing to the dissipation rate. if
> it does not make a big difference then I would say your LES with 32^3 and
> f=0.05 is pretty good.
> (2) how does the time history in all cases compare to Brachet et al. (see
> my previous note) at the same Re.
>
> Ammar
>
> On Dec 8, 2012, at 3:01 PM, nek5000-users at lists.mcs.anl.gov wrote:
>
> Your results make sense to me.  Note that you are not really "capturing"
> peak dissipation rate with filtering.
> you are only supplementing the resolved dissipation on a given grid by
> artificially damping energy.   that's why you get higher peak with f=0.05
> and N=14^3 relative to  f=0  and N=14^3
> I wonder how much resolution N^3 you need (with f=0) to truly capture the
> peak dissipation rate?
>
> In order to better judge your simulations you should compare DNS (f=0) and
> LES f=nonzero for gradually increased resolution N^3
>
> if DNS is expensive , good news DNS is already been done , Check Brachet
> et al JFM article  Journal of Fluid Mechanics<http://journals.cambridge.org/action/displayJournal?jid=FLM> /
> Volume 130 / May 1983, pp 411-452
> (
> Small-scale structure of the Taylor–Green vortex*Marc E.  Brachet a1p1<http://journals.cambridge.org/action/displayAbstract;jsessionid=2541E59358A427C052F22128A3D13BCC.journals?fromPage=online&aid=376272#p1>
> *, *Daniel I.  Meiron a1*, *Steven A.  Orszag a1*, *B. G.  Nickel a2*
> )
>
>
>  and compare the time history of the dissipation rate
> to what you get at the same Reynolds number.
>
>
>
> Ammar
>
>
>
>
>
>
> On Dec 8, 2012, at 2:36 AM, nek5000-users at lists.mcs.anl.gov wrote:
>
> Hello
> I am solving the 3-D Taylor-Green problem as described here
>
> http://www.dlr.de/as/desktopdefault.aspx/tabid-8170/13999_read-35550/
> C3.5 Direct Numerical Simulation of the Taylor-Green Vortex at Re = 1600<http://www.as.dlr.de/hiocfd/case_c3.5.pdf>
>
> using NEK.
>
> I use
>
> lx1 = 10
> lx2 = lx1-2
> ldx = 15
>
> No of elements = 14^3 or 28^3
>
> The evolution of dissipation rate with time is shown in attached pdf.
>
> f=0.0 indicates no filtering and f=0.05 means filter parameter P103.
>
> Use of filter seems to capture peak dissipation rate better but still some
> difference is seen. The DG results with similar number of dofs in the
> problem description give good estimate of peak rate. So I expect NEK
> results to improve further and would like to ask for any advice. Should I
> try with larger amount of filtering ?
>
> I have attached my SIZE and rea files.
>
> Thanks
> praveen
> <box.rea><diss.pdf><SIZE>_______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20121209/203f8266/attachment-0001.html>