[Nek5000-users] Linearised Navier-Stokes: 2D cylinder flow

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

Hi Paul,

I have simply used the ext_cyl.rea and .map files so I guess it is
dirichlet boundary condition at the inlet (which I have set to zero in
usrbc since I am looking at perturbations), periodic boundary conditions on
the sides, no-slip condition on the wall of the cylinder and classical
outflow condition at the outlet.

I initially thought this could come from the fact I had been using a call
to random_number to initialise vxp and vyp. I made sure to use dsavg to
ensure that the velocity on each side of the interface between elements has
the same value. It did not change anything. I also tried with a hand-made
divergence-free perturbation. Did not changed anything either. I am kind of
clueless, particularly because it works fine with all of my other cases.
Attached are the files I am using if you want to peak a glance at them.

Cheers,
JC


2014-02-06 5:11 GMT+01:00 <nek5000-users at lists.mcs.anl.gov>:

>
> Hi JC,
>
> Are you trying to look at the perturbation from the
> steady cylinder base flow ?
>
> Am curious about your boundary conditions (though I
> recognize that your bc set for the external cylinder
> flow shouldn't be too different from the boundary
> layer case)...
>
> Just inquiring to get a better idea of what's going on.
>
> Paul
>
>
>
> On Wed, 5 Feb 2014, nek5000-users at lists.mcs.anl.gov wrote:
>
>  Hi Nek's,
>>
>> I am trying to run a linearised DNS of the flow over a two-dimensional
>> cylinder at Re=60 for illustration purposes using the ext_cyl example. I
>> am
>> however encountering some troubles... I have been able to compute the
>> unstable steady equilibrium using a selective frequency damping approach
>> without any trouble. However, it is quite a different story when it comes
>> to the linearised DNS. Indeed, the perturbation velocity field blows up
>> quite rapidly and I am not sure why. I have tried other flows (lid-driven
>> cavity, boundary layer, ...) just to make sure I had no problem with  my
>> nek install and everything was running fine. I have also tried on three
>> different computers to make sure it was not platform-dependent and it
>> actually blew up every time. I have been using the linearised version of
>> nek quite extensively for the past three years and but never had such
>> problem.
>>
>> Is there something I have missed there?
>>
>> Thanks a lot,
>> JC
>>
>> --
>> Jean-Christophe Loiseau
>> Homepage <https://sites.google.com/site/loiseaujc/>
>>
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>



-- 
Jean-Christophe Loiseau
Homepage <https://sites.google.com/site/loiseaujc/>
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