[Nek5000-users] Infinite Prandtlnumber with Nek5000

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

Hello Lailai,
I see oscillations in the velocity field with a period dependent on the 
time step (shorter timesteps result in faster oscillations), which only 
decay very slowly. I haven't tested increasing the resolution here, this 
might  be the reason. However, the method outlined by Paul seems to work 
fine at the same resolutions and converges very fast. The big caveat 
here is that I haven't tested the results against other codes or 
theoretical predictions yet. I am not working on the subject of inf. 
Prandtlnumber flows myself, but other members of my group were 
interested in Nek5000, so I gave it a try.

Cheers,
Jan

On 08/15/2015 12:43 AM, nek5000-users at lists.mcs.anl.gov wrote:
> hello, Jan,
>
> great that you have tested them. I always want to try, but am too lasy...
> Could you say a little bit about the aphysical
> oscillations? Do you see oscillations for one iteration, or they 
> appear because of the
> time stepping approach I suggested? Sometimes I indeed see this in the 
> velocity field
>  for a low-quality mesh with low GLL numbers, normally the spatial 
> velocity oscillations
> are gone by either using a mesh with better quality (same GLL) or 
> increasing the number GLL points for
> the same mesh.
>
> I think the way suggested by Paul will significantly speedup the 
> simulation compared to the way
> I suggested, although trivial inertia is introduced.  have you 
> observed the speedup?
>
> thanks,
>
> lailai
>
> On 2015/8/14 9:00, nek5000-users at lists.mcs.anl.gov wrote:
>> Hi Paul,
>> thanks for the advice. I tested some simple 2D cases and the method 
>> seems to work quite good. The idea in the other posts had a tendency 
>> to produce unphysical oscillations. We might look into testing Nek 
>> against other mantle convection codes, where varying viscosity and 
>> parallelisation is still a problem.
>>
>> Thanks again,
>> Jan
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>

-- 
----------------------
Jan Vormann
Institut für Geophysik
Corrensstr. 24
D-48149 Münster