[Nek5000-users] rotating disk with periodic boundaries

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

Dear nek users,
I am doing simulations over a rotating disk with nekton and would like to
decrease my domain in order to save computational time.

The mesh is currently very similar to that of a pipe, with inflow in one
end
(max(z)) and a rotating wall in the other end (z=0). Around the curved
edges I use the outflow boundary condition.

The way I would like to decrease the domain in is by using periodic
boundary conditions in the rotational direction, that is cutting the
pipe in the
z-direction to only use a third or a quarter of the pipe.

My problem is that when I try to do this, I have to make one element
periodic
with itself, this is since I would like to have few elements in the
middle of
the domain and thus not want to use the cylindrical coordinates.

In some setups, I recieve an error when using genmap (when trying
different mesh
tolerance numbers), and in some setups I get a communication error when
running
the code;


genmap error:

  4   z1    0.0000E+00  1.5224E-01  1.5224E-01  0.0000E+00
       2 3  3  1.00000005E-03  1.00000000E+00 abort: FACE MATCH FAIL
       7 4  5  1.00000005E-03  2.54558474E-01 abort: FACE MATCH FAIL


communication error:

veryfy mesh topology ...
...
...
WARNING1 Element mesh mismatch at:
i,j,k,ie:    1    1    1    1
Near X = 0.59397000    0.59397000    0.00000000    , d:    0.0000000  
 -0.11313799    1.4142136
...
...



The type of error seem to depend on how the elements are numbered in the
domain.

I've understood that for using the periodic boundary conditions, one
need at
least three elements. Is there a way around this when it comes to my setup?
Or would there be an easy fix for this problem?


Best regards,
Ellinor
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