[Nek5000-users] Perturbation mode

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

Hi JC,

There may also be an issue with having the projection turned on.
(This is a common source of NaN...).   I suggest setting p93-95 to 0
in the .rea file.  (We can subsequently fix the problem correctly.)

Are you trying to run with a steady-state base flow, or an evolving
base flow?

I'm out of the office today but can hopefully look into this in
the next day or two.   To date I've not done a lot of perturbation
cases, so there are likely a few issues to resolve.  Several groups
have had some success, however.

Regards,

Paul


On Wed, 16 Feb 2011, nek5000-users at lists.mcs.anl.gov wrote:

> Hi Jean-Christophe,
>
> I think the restart option does not work properly in the perturbation
> mode. That means, in the rea-file you can just give the base flow under
> RESOLVE/RESTART OPTIONS.
> I usually do the restart of the perturbation manually in the user-file.
> Another way is to change that in the source code.
>
> David
>
> nek5000-users at lists.mcs.anl.gov wrote:
>> Hi Nek's,
>>
>> I am still struggling with the perturbation mode.
>> Cavity_20x20x10_6x6x6_R1000_25D0.f00001 contains my base flow. It is a
>> 2D lid-driven cavity extruded in the third direction (z).
>> Perturbation_20x20x10_6x6x6_25D0.f00001 contains my divergence-free
>> perturbation. It is subject to no-slip conditions at the walls and
>> periodic BC at zmin and zmax.
>>
>> Following is how I set it up.
>>
>> **********************************************
>>
>> In my blah.rea
>>
>> -1.           p31 NPERT: #perturbation modes
>>
>> [...]
>>
>> 2 PRESOLVE/RESTART OPTIONS *****
>> Cavity_20x20x10_6x6x6_R1000_25D0.f00001
>> Perturbation_20x20x10_6x6x6_25D0.f00001
>>
>> **********************************************
>>
>> In SIZE:
>>
>> parameter (lpelv=lelv,lpelt=lelt,lpert=1) ! perturbation
>> parameter (lpx1=lx1,lpy1=ly1,lpz1=lz1) ! array sizes
>> parameter (lpx2=lx2,lpy2=ly2,lpz2=lz2)
>>
>> **********************************************
>>
>> I have tried with various initial amplitude for the perturbation, and
>> various time steps. However, I always have a very small CFL and after
>> six timesteps I get:
>>
>>     Failed in HMHOLTZ: VELX NAN
>>
>>
>> Same for vely and velz. I may have missed a key point but being not
>> particularly familiar with Nek numerics yet I'm not sure where I
>> missed it.
>>
>> Best regards,
>> --
>> Jean-Christophe
>> ------------------------------------------------------------------------
>>
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>
>
> -- 
> David Tempelmann
> Linné Flow Center, Mechanics KTH
> SE-100 44, Stockholm, Sweden
> Phone: +46 8 7907161
> E-mail: david at mech.kth.se
>
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