[Nek5000-users] Project a solution onto a polynomial space

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

Hi,
just out of interest, are you sure that you need dealiasing for 
statistics? Some long time ago, I tried it as well, and compared it to 
non-dealiased statistics, and I could not really see a difference. I 
guess my argument at the time was that you are interested in the 
low-frequency content of the statistics anyway, so that the aliasing 
errors would not show up.

Are you then planning to increase the polynomial order such that you can 
completely eliminate the qudrature errors even for third order terms?

Best regards,
Philipp

On 2017-03-22 18:21, nek5000-users at lists.mcs.anl.gov wrote:
> Dear Paul,
>
>
> Thank you for answering so quickly. Yes, the polynomial spaces I'm using
> are the standard Nek5000 basis functions.
>
>
> To understand the problem a little better:
>
> I am conducting DNS of a shear flow and I need to compute higher-order
> velocity moments. I've implemented some subroutines based on the "avg2"
> and "avg3" subroutines from Nek, but for higher order moments, i.e.
> <U^3>, <U^2 V>, etc. The problem is that I need to de-alias the
> non-linear quantities, i.e. U^3, before doing the averaging. Since the
> flow is planar, I also take the spanwise average using the "z_average"
> subroutine.
>
>
> I checked out the "convect.f" file to see how dealiasing is applied by
> mapping onto the finer grid (lxd), but I'm not quite sure how to project
> these results back onto the original grid.
>
>
> Thank you,
>
>
> Juan Diego
>
>
>
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