[Nek5000-users] Nonzero swirl velocity at the centerline

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

Dear Outi,

Do you have the "A  " bc on your elements that touch the centerline?

Are you using the same mesh as vortex2? Or a new one generated with
genbox.

In principal, the A bc should set U_theta=0 on the axis.

Paul


On Sat, 6 Oct 2012, nek5000-users at lists.mcs.anl.gov wrote:

> Dear Neks,
>
> I have started to use the 2D axisymmetric version of Nek5000 with swirl (like 
> the example vortex2), to get some base flows in axisymmetric geometries.
> To test the code I modified the vortex2 example to simple Grabowski vortex 
> flow.
> This means setting the inlet profile:
> U_x=1
> U_r=0
> U_theta=0.8944r(2-r^2)
>
> The result looked good at the first sight, but a closer inspection revealed 
> that the swirl velocity (U_theta) is nonzero at the centerline (up to 
> U_theta=0.1). Also other axisymmetric flow cases with swirl gave nonzero 
> swirl velocities.
>
> I wonder if it would be possible for someone to look into why this happens? I 
> have attached the .usr, .rea and .box files below.
>
> Also, it would be useful if you could guide me into the precise place in the 
> code where the centerline condition for swirl is set. Does OMASK have 
> something to do with this? Or is it TMASK?
>
> Outi
>