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-   -   3D axissymmetric problem (http://www.cfd-online.com/Forums/openfoam/77754-3d-axissymmetric-problem.html)

noramat July 2, 2010 07:12

3D axissymmetric problem
 
hello,

i have to solve a axis-symmetric 3D-problem (cylinder) - magnetohydrodynamic problem coupled with boussinesq-approximation. Is there any way to solve it in OpenFoam without cylindrical coordinates and without the wedge condition, only with a special boundary condition!? So - maybe - through a constant azimuthal (theta direction) component!? But how could i implement such a condition?

Thanks a lot.

noramat

marcbest July 2, 2010 07:30

i'm also a starter at OF and i'm not familiar with magnetohydrodynamics in OF but generally 2D Simulations can be done with wedges
if you want to define a new boundary condition you have to programm and compile it, have a look at:
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2007/
http://www.tfd.chalmers.se/~hani/kur...yCondition.pdf
Implement boundary condition

i hope this helps

maddalena July 2, 2010 07:45

Hi,
Quote:

Originally Posted by noramat (Post 265439)
i have to solve a axis-symmetric 3D-problem (cylinder) ... Is there any way to solve it in OpenFoam without cylindrical coordinates and without the wedge condition, only with a special boundary condition!?

If your case is 3D, you should use a cyclic bc and not a wedge, which applies only on 2D problems (one cell thick). If you apply cyclic, it is not necessary to convert everything in cylindrical coordinates, but cartesian will be ok.
Hope this helps.

cheers,

mad

noramat July 13, 2010 16:07

thanks for your answers!

now i have another question to wedge-type ..

so - wedge-type is used for 2d-axisymmetric problems. Does the wedge-type imply, that all quantities are independent of the angular/azimuthal component phi (constant in phi direction) and that the angular/azimuthal velocity u_phi is zero?

If the last fact is not true (u_phi = 0), how could i implement that? Maybe through a special boundary condition again?

thanks a lot again!

noramat

maddalena July 13, 2010 16:43

Hi Noramat,
I am not sure I understand your question correctly but... Wedge type is 2D. OF does the trick of using a 3D mesh to solve a 2D case, but in reality all your properties are (and remain) constant along the third dimension, which is not solved indeed. Thus I would say yes:
Quote:

Originally Posted by noramat (Post 267112)
the wedge-type imply, that all quantities are independent of the angular/azimuthal component phi (constant in phi direction) and that the angular/azimuthal velocity u_phi is zero

hope that helps

mad

noramat July 14, 2010 05:22

thanks again!

that's one answer i need :)

but now i'm still not sure because of the other fact.. so i have to solve a axisymmetric problem (zylinder) with the condition that the angular velocity u_phi is zero. but is it realised by wedge-type?

thanks!

normat

maddalena July 14, 2010 05:53

Hi Noramat,
is U_phi the angular velocity? If it is, than u_phi will be zero, since the angular direction is not solved by OF. On the other hand, if you are interested on an angular direction, than your problem is not 2D. Indeed, you have two geometrical directions (radial and axial) + one phisical direction (circonferential, or angular, as you like), thus the problem is 3D. In that case, the wedge bc cannot be applied and you should use a cyclic instead.
hope that this makes things clearer.
cheers,

mad

noramat July 14, 2010 05:58

thanks very much!


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