[Nek5000-users] Corner elements giving large values

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

Hi NekForum, Paul

      I intent to have isothermal conditions at the inner and outer
cylinders. The differential heating is achieved by imposing a
temperature difference across the two cylinders. I have used T = 1 and
0 values for non-dimensional temperature. I think it should be fine.
Do you see any problem here.

Thank you
Swarandeep

On Thu, Jun 1, 2017 at 11:28 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>
> Hi Swarandeep,
>
> Is 0/1 a realistic BC for T ?
>
> Best,
>
> Paul
>
> ________________________________________
> From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
> Sent: Thursday, June 01, 2017 12:53 PM
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Corner elements giving large values
>
>  Hi Nek Forum, Paul
>
>        I am having temp = 1 and temp = 0 at the inner and outer
> boundaries. Gravity is pointing in the -ve z-direction along the axis
> of the
>      annulus.  The top and bottom planes have zero heat flux conditions.
>        I have Coriolis force added as a body force.
>        The Rayleigh number is around 10000. The resolution is 8, 25,
> 24 elements in the r, phi and z directions respectively with order 9.
>        My initial condition is very low arbitrary velocity
> perturbation (~10^(-8)). The time resolution is set to 10^(-5) for
> param12. The CFL is
> set to 0.5. Please indicate how to control it.
>
>       As you have rightly mentioned, I start the simulation with a
> very low value of the Rayleigh number and gradually increase it. Yet,
> the corner values only get large. Other regions of the domain are
> fine.
>
> Thank you
> Swarandeep
>
> On Thu, Jun 1, 2017 at 7:38 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>>
>> Hi Swarandeep,
>>
>> How large is your Rayleigh number and what is your resolution?
>> What are your thermal bcs?  What are your ICs?
>>
>> There should be no particular issue with your configuration - but you do need to
>> control spatial and temporal resolution.
>>
>>
>> For RB, you often have to start at low Ra and/or small dt because the nonlinear
>> response can often drive the velocities to be quite high very rapidly before the
>> CFL constraint kicks in.   RB flows are one of the rare instances where I use
>> variable time step size (param 12 > 0), but even then you have to keep the target
>> CFL quite small until the flow is established.
>>
>> hth,
>>
>> Paul
>>
>> ________________________________________
>> From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
>> Sent: Thursday, June 01, 2017 7:27 AM
>> To: nek5000-users at lists.mcs.anl.gov
>> Subject: [Nek5000-users] Corner elements giving large values
>>
>> Dear Nek forum,
>>
>>       I am simulating Rayleigh Benard flow in a 3D finite cylindrical annulus.
>>       I am getting spurious large values of velocity at the corner regions
>>       of the annulus i.e. the edges where the inner cylinder joins the
>> top and bottom
>>       planes. The boundary condition is no-slip and no penetration for velocity
>>       at these edges. Can someone point out a plausible reason.
>>
>> Thank you
>> Swarandeep
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