[Nek5000-users] Nonzero swirl velocity at the centerline

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

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

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