[Nek5000-users] Internal boundary condition

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

Thanks Paul!
I am also thinking of having a precursor simulation of flow inside  
nozzle and therefore, replacing it with a prescribed inflow BC.

Mohsen

On 21-Apr-14, at 8:00 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

>
> Dear Mohsen,
>
> Years ago we did support internal walls, but that's no longer the  
> case with the current workflow.
>
> The issue is that the gridpoints across the interface are  
> identified as being one and the same if
> they are physically adjacent.  It would be possible to hack into  
> your vertex numbering to make
> these different (i.e., after they are generated by genmap), or to  
> make a geometry in which they
> are distinct by having a finite-thickness wall, but either way  
> requires some application specific
> coding in your usr file or modifications to your map file.
>
> 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: Monday, April 21, 2014 6:12 PM
> To: Nek 5000
> Subject: [Nek5000-users] Internal boundary condition
>
> Dear all,
> I have a question regarding the internal boundary condition in the  
> code.
> My problem consists of a fan-shaped nozzle, which parts of its  
> walls are located within the flow domain (a cylindrical tank with  
> inflow/outflow boundary conditions). The question is how to set the  
> boundary conditions for such internal zero-thickness walls?
>
> I thought the walls could be defined as internal faces by creating  
> a side-set (in the Cubit) and setting the velocity and the  
> temperature fields of these faces to 'W  ' and 'E  ', respectively,  
> similar to the solid-fluid interface  in the conjugate heat  
> transfer example. Nevertheless, there is a fluid at both sides of  
> the interface in this case.
> Below is part of the boundary conditions in .rea file.
> .....
> .....
> 1 0     ! 1 fluid set, 0 other/solid sets
> 10     ! fluid set is 10
> 1 ! block 10 is material 1
> 10       ! no. bc sets (side-sets); bc set id,
> 100  1    W  , (external walls)
> 100  2    I  , (external walls)
> 120  1    W  , (internal walls corresponding to the nozzle)
> 120  2    E  , (internal walls corresponding to the nozzle)
> 200  1    v  , (inflow)
> 200  2    t  , (inflow)
> 300  1    O  , (outflow)
> 300  2    O  , (outflow)
> 400  1    SYM,
> 400  2    SYM,
> .....
> .....
>
> When I run this case, warning messages appear during assigning the  
> sidesets to the element faces, saying that: "face shared by 2 Hexes  
> (say) 2331 5227". It seems that this warning is only because I  
> defined some faces as "internal", however, no "other solid/fluids"  
> has been defined in the input file.
> Nevertheless, the issue with such definition is that, although, the  
> velocity field is zero at the internal walls, there seems to be a  
> pressure gradient across the wall, which is not physically  
> consistent with internal walls, and drives a flow through the walls.
>
> It would be appreciated if anyone could help me on this problem.
>
> Thanks,
> Mohsen
>
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