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-   -   AXIS BOUNDARY-CONDITION in Dispersed Phase Flow (http://www.cfd-online.com/Forums/main/1521-axis-boundary-condition-dispersed-phase-flow.html)

Remesh K November 11, 1999 08:30

AXIS BOUNDARY-CONDITION in Dispersed Phase Flow
 
Dear friends,

I am simulating dispersed flow using Fluent V 4.32. I have a problem with axis boundary condition. I set the CELL-TYPE of centre line of the Nozzle as the AXIS. But in SETUP-2 LIST-BOUNDARY the boundary condition is seen to be taken as SYMMETRY REFLECT and the particle found to reflect on hitting the AXIS. But this is undesirable and the particles should pass through as if in the LIVE cell. How to change the BOUNDARY-CONDITION of AXIS to a suitable one, so that the particles will pass through?

Could anyone help me? Your help will be greatly appreciated.

Remesh.


John C. Chien November 11, 1999 11:34

Re: AXIS BOUNDARY-CONDITION in Dispersed Phase Flow
 
(1). I think, the axis is only related to the coordinate system, the flow does not know whether there is an axis or not. (2). I would say that it is a 3-D problem. In the 3-D problem, there is no boundary condition at the axis.

Jin Wook LEE November 11, 1999 21:03

Re: AXIS BOUNDARY-CONDITION in Dispersed Phase Flow
 
Mathematically, axis does not have any volume, and it is treated similarly as 'symmetry line in 2D case'. So, I think that there is no way(I am not quite sure) except to impose symmetry reflect boundary condition'. I think that it is perfect for 2D case(in Fluent, symmetry cells), and it might be fairly O.K. to use default 'symmetry reflect' if you have enough cells near the axis for 3D case. After reflecting small distance, it will proceed to its own way. There might be small error.

If you really want to impose passing condition, you should not generate your grid system by polar(or cylindrical) coordinates. Instead, you should generate grid system by BFC or UNS based on Cartesian coordinates, then there is finite volume cells at the axis. Then your axis is consist of live cells with finite volume, not any more boundary cells, and particle does pass the axis.

Sincerely, Jinwook

Guosheng Kang November 16, 1999 23:44

Re: AXIS BOUNDARY-CONDITION in Dispersed Phase Flow
 
I guess you forgot to change the boundary type when you set the boundary, Change it from "symmetry" type to "axis" type, it will work. By the way, the inlet direction should be in x-direction. Hope this is not too late.

Guosheng


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