[Nek5000-users] Rules of thumb for element aspect ratio limits

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

·HI Matt,

Till now I have no experiments on 3D problem, what I am interested in is
how you generate the 3D or 2D airfoil mesh for nek5000? I spend 2 weeks in
generated a 2d airfoil flow mesh without any good results. would you like
tell me some informations? thank you a lot!

Wei


2014-04-25 17:00 GMT+02:00 <nek5000-users at lists.mcs.anl.gov>:

> Hello,
>
> I am looking to do simulations of flow past a wing in 3D using nek5000 and
> I have been thinking more about potential issues with high aspect ratio
> elements. In general we have very fine resolution near the wing and then as
> we get further away the wall normal and wall parallel spacing increases. As
> a first try we will extend the domain in the cross stream direction which
> will result in small dz values. I know that in general the best performance
> is obtained with elements having dx=dy=dz and that as the aspect ratio
> increases the performance will degrade.
>
> I'm wondering if there are general rules of thumb for the performance
> degradation with increased aspect ratio. For example, is an aspect ratio of
> 10 ok but an aspect ratio of 100 unacceptable? Is this even something we
> can estimate in general or does it vary so much problem to problem that no
> general estimate is possible?
>
> I saw an earlier post that referred to the paper "An Overlapping Schwarz
> Method for Spectral Element Solution of the Incompressible Navier-Stokes
> Equations", P. Fischer JCP 1997. From the paper I see two general
> strategies.
> 1. limit the maximum aspect ratio to a critical value
> 2. design a grid for our case, run it for a short time and then
> iteratively add more grid points to decrease the aspect ratio until optimal
> performance is achieved.
>
> Does anyone have a general or specific suggestion regarding how we should
> handle the grid generation in terms of selecting the largest aspect ratio
> possible with low computational cost?
>
> Thanks,
>
> Matt
>
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