[Nek5000-users] Location based viscosity

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

Hi Josh,

PnPn generally works better for highly turbulent marginally
resolved cases (the add'l pressure modes are useful).

That solver is not quite up to the performance of the PnPn-2
yet - the pressure solver needs to be updated as soon as I
get a chance - so the iteration counts are higher.

The PnPn-2 stress formulation has been more extensively tested.
For PnPn, you need to treat the variable stress explicitly,
which means setting ifexplvis to true, as well as ifuservp.
(See turbChannel example.)

For moving meshes, you must use PnPn-2.   For low Mach, PnPn.

Paul


On Thu, 24 Mar 2011, nek5000-users at lists.mcs.anl.gov wrote:

> Thanks Paul and Aleks, that helps a lot!
>
> I'm using Pn-Pn right now, but I think I'll switch to Pn-Pn-2 shortly.
> I understand the difference between the two formulations, but is
> there a reason where one might use one formulation over the other?
> (stability, speed, etc...)  (Sorry if this question is off-subject)
>
> Josh
>
>
> On Thu, Mar 24, 2011 at 10:06 AM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>> Hi Josh,
>>
>> make sure you accivating a call to uservp by either setting
>>
>>      ifuservp = .true.
>>
>> say in usrdat2 passed through 'TOTAL' or by p30>0 in .rea
>>
>> Best,
>> Aleks
>>
>>
>>
>> On Thu, 24 Mar 2011, nek5000-users at lists.mcs.anl.gov wrote:
>>
>>>
>>> Hi Josh,
>>>
>>> How about setting "udiff" in uservp?
>>>
>>> Note that if you have more than one field (e.g., temperature and velocity)
>>> then you discriminate by ifield:
>>>
>>>     if (ifield.eq.1)  then  ! viscosity
>>>
>>>        udiff   = my viscosity
>>>        utrans  = my rho
>>>
>>>     elseif (ifield.eq.2)  then  ! conductivity
>>>
>>>        udiff   = my conductivity
>>>        utrans  = my rho C_p
>>>
>>>     endif
>>>
>>>
>>> Note that technically, you should use the full stress tensor
>>> when doing this, since the d/dxj mu du_j/dx_i
>>> term no longer vanishes.
>>>
>>> Are you using PnPn, or PnPn-2 ?
>>>
>>>
>>> Paul
>>>
>>>
>>> On Thu, 24 Mar 2011, nek5000-users at lists.mcs.anl.gov wrote:
>>>
>>>> Hello Neks,
>>>>
>>>> This seems like it should be simple, but can somehow show me how I can
>>>> vary viscosity based on a given x, y, z?
>>>>
>>>> I'm guessing I should be able to do this in uservp, looking at the
>>>> var_visc example, but I don't immediately see a variable that I can
>>>> edit in NEKUSE (like I could for ux, uy, etc....)
>>>>
>>>> Thanks,
>>>>
>>>> --
>>>> Josh Camp
>>>>
>>>> "All that is necessary for the triumph of evil is that good men do
>>>> nothing" -- Edmund Burke
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>
>
>
> -- 
> Josh Camp
>
> "All that is necessary for the triumph of evil is that good men do
> nothing" -- Edmund Burke
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