[Nek5000-users] Uservp, eddy diffusivity and explvis

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

Markus,

don't use the characteristics scheme when ifexplivs is true otherwise you may run into a stability problem if your dt is too large. If you use the PN/PN-2 formulation ifexplvis has no effect and you have to make sure to use the stress-formulation to support a variable viscosity.

Stefan


-----Original Message-----
From: nek5000-users-bounces at lists.mcs.anl.gov on behalf of nek5000-users at lists.mcs.anl.gov
Sent: Sun 7/25/2010 22:14
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Uservp, eddy diffusivity and explvis
 
Hi,

thanks for clarifying, I'll keep it turned on.
I tried both IFCHAR true and false, the error is the same.

I also tried to reproduce the error on a coarser geometry, similar Re 
and geometric features, but I couldn't - adding some diffusivity while 
USERVP and explvis are true worked. So I tend to think it is some 
specialty within my simulation.

What helps, however, is to switch from PN-PN to PN-PN2. Then, the 
simulation behaves OK.

So I'll work with that for now.

Markus


nek5000-users at lists.mcs.anl.gov wrote:
> Ok if is changing you have to set ifexplvis = .true.
> Are you using IFCHAR=.true.?
> 
> On Jul 20, 2010, at 1:56 PM, nek5000-users at lists.mcs.anl.gov wrote:
> 
>> No, it's changing in time and space since it's computed with an eddy diffusivity model. But when I turn ifexplvis on, the simulation crashes after very few time steps due to crazy velocities - even though I don't change viscosity for trial purposes.
>>
>> Markus
>>
>>
>> nek5000-users at lists.mcs.anl.gov wrote:
>>> Is your viscosity constant?
>>> Stefan
>>> On Jul 20, 2010, at 12:18 PM, nek5000-users at lists.mcs.anl.gov wrote:
>>>> Hi,
>>>>
>>>> can I leave "ifexplvis = .false." when doing a nek simulation with user defined viscosity and PN/PN?
>>>>
>>>> Markus
>>>>
>>>> _______________________________________________
>>>> Nek5000-users mailing list
>>>> Nek5000-users at lists.mcs.anl.gov
>>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>> _______________________________________________
>>> Nek5000-users mailing list
>>> Nek5000-users at lists.mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> 
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> 
_______________________________________________
Nek5000-users mailing list
Nek5000-users at lists.mcs.anl.gov
https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users