[Nek5000-users] Linearised Navier Stokes

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

Hi again,

Regarding the runs, the typical way is to have a /fixed/ base flow, and 
a disturbance developing on top of that base flow. In this case, npert 
used to be set to a negative number, and you would need to provide the 
base flow; typically obtained from a previous simulation (perhaps a 
stabilised run with SFD or Newton, or a turbulent mean). Note that for 
specific applications, you can also change the base flow in time (e.g. 
for studying the stability of a limit cycle).

The base flow can also evolve in time using NS. In this case, npert>0, 
and both disturbances and base flow change with time.

Hope this helps,
philipp

On 2017-08-10 16:53, nek5000-users at lists.mcs.anl.gov wrote:
> Hi Philipp,
> I am using the latest version. Thanks for the help. Until I get the
> relevant instructions can you please tell me the following:
> 
>   Do I have to do separate runs for base and perturbations or the base
> state can be incorporated into perturbation run and a single run be
> performed.
> 
> Thanks
> Swarandeep
> 
> On Thu, Aug 10, 2017 at 7:42 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>> Are you using the latest git version? If so, I think I cannot give you the
>> procedure as my knowledge is a bit old. But I can ask Adam next week to give
>> you these instructions. Sorry about that.
>>
>> But in general, the buoyancy forcing for the perturbations should go into
>> userf as it does for the base-flow calculation.
>>
>> Or perhaps somebody else could give the guidelines for the new release?
>>
>> Philipp
>>
>>
>> On 2017-08-10 15:01, nek5000-users at lists.mcs.anl.gov wrote:
>>>
>>> Hi Philipp,
>>>
>>>        Can you please outline the procedure to be followed for
>>> calculating the perturbed velocity and temperature field based on the
>>> following information.
>>>
>>>       I have a 3d annulus domain with vertical gravity pointing downward
>>> and temperature gradient in the radial direction.
>>> This leads to a base flow about which I have to linearize the problem.
>>> Please let me know how to include the information of the base flow and
>>> base temperature gradient into the perturbation calculations.
>>>
>>> Thank you
>>> Swarandeep
>>>
>>> On Thu, Aug 10, 2017 at 5:51 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>>>>
>>>> Hi,
>>>> the linearised version is included in the main version of the code. You
>>>> activate perturbations by setting NPERT different from zero. The relevant
>>>> routines in the code are collected in the file perturb.f.
>>>>
>>>> Hope this helps,
>>>> philipp
>>>>
>>>>
>>>> On 2017-08-10 12:56, nek5000-users at lists.mcs.anl.gov wrote:
>>>>>
>>>>>
>>>>> Hi Nek Forum,
>>>>>
>>>>>        How to obtain the linearised version of the Nek5000 code. Please
>>>>> advice.
>>>>>
>>>>> Thanks
>>>>>     Swarandeep
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