[Nek5000-users] Perturbation mode

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

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