CFD Online Discussion Forums - Axisymmetric Case 3rd Velocity Component

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Axisymmetric Case 3rd Velocity Component

Hi Folks,

I'm solving an axisymmetric Pipe-Flow with wedge boundary conditions. On watching the residuals, I was wondering why why all 3 velocity components are solved (see Picture below). Due to the U_y velocity residual my simulation never converges.

The wedge angle is 2deg on both sides, so less than 5deg. My blockMesh looks like this:

Code:

convertToMeters 0.001;



vertices

(

    (0 0 -315)

    (5.25 -0.18333404 -315)

    (5.25 0.18333404 -315)

    (0 0 -315)

    (0 0 0)

    (5.25 -0.18333404 0)

    (5.25 0.18333404 0)

    (0 0 0)



    (0 0 1000)

    (5.25 -0.18333404 1000)

    (5.25 0.18333404 1000)

    (0 0 1000)



    (12.5 -0.43650962 0)

    (12.5 0.43650962 0)

    (12.5 -0.43650962 1000)

    (12.5 0.43650962 1000)



    (100 -3.4920769 0)

    (100 3.4920769  0)

    (100 -3.4920769 1000)

    (100 3.4920769  1000)



);



blocks

(

    hex (0 1 2 0 4 5 6 4) (3 1 158) simpleGrading (0.6 1 0.8)

    hex (4 5 6 4 8 9 10 8) (3 1 500) simpleGrading (0.6 1 1.5)

    hex (5 12 13 6 9 14 15 10) (3 1 500) simpleGrading (1.2 1 1.5)

    hex (12 16 17 13 14 18 19 15) (40 1 500) simpleGrading (1.5 1 1.5)



);



edges

(

);



boundary

(

    symmetry

    {

      type symmetryPlane;

      faces

    (



     (0 4 4 0)

     (4 8 8 4)

     

     );

    }



    inlet

    {

        type inlet;

        faces

        (           



     (2 0 0 1)

        

        );

    }



    pilot

    {

        type inlet;

        faces

        (           



     (13 6 5 12)

        

        );

    }





    coflow

    {

        type inlet;

        faces

        (           



     (17 13 12 16)

        

        );

    }



   surrounding

    {

      type patch;

      faces

    (



     (18 19 17 16)



     );



    }



    wall

    {

        type wall;

        faces

        (           



     (2 1 5 6)

        

        );

    }



    outlet

    {

        type outlet;

        faces

        (           



     (8 8 10 9)

     (10 15 14 9)

     (15 19 18 14)

        

        );

    }



    rotper1

    {

      type wedge;

      faces

    (



     (1 5 4 0)

     (5 9 8 4)

     (12 14 9 5)

     (16 18 14 12)



     );

    }

     

    rotper2

    {

      type wedge;

      faces

    (



     (6 2 0 4)

     (10 6 4 8)

     (15 13 6 10)

     (19 17 13 15)



     );

    }







 

);



mergePatchPairs

(

);

http://s28.postimg.org/vl3z5s499/Residuals.png

Regards
Philipp

Hi Philipp,

I have noticed the same thing too and I think this behavior is very common for Axisymmetric cases with simpleFoam type solvers. I think (although I am not 100% sure) that the third velocity component (Uz) is solved to account for an axisymmetric swirl component and to include the possibility of giving a swirl component to the inlet velocity. Of course, most simple cases like pipe flows, we specify the Uz component at the inlet zero and the swirl actually doesn't develop.

I think in your case, we don't need to look at the U_y residual development - we can safely conclude that the solution is converged after 600 iter.

regds
kumar

I agree with Kumar here. I've recently compared simpleFoam axisymmetric against simpleFoam with the full three-dimensional geometry. Though lacking convergence in Y, the other two components converged and matched up with the full model quite nicely. I believe there is nothing to worry about.