[Nek5000-users] Nonzero swirl velocity at the centerline

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

Dear Outi,

If you are prescribing your u_theta (i.e., as temperature),
then from your formula below it should be zero on the axis.

One thing that might be of value (for small problems) is
to add to userbc the statements below

        if (ifield.eq.2) write(6,1) x,y,temp
      1 format(1p3e13.5,' uxyz')
        if (istep.eq.2) stop

You can then grep uxyz logfile and look at what is going on.
You should see that, for y=0, you match your desired profile.

Paul



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

> Dear Paul,
>
> I use the "A  " BC.
> And the new mesh generated by genbox.
>
> Outi
>
>
> 6 Oct 2012 kl. 23:28 skrev 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
>>> 
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