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Old   June 18, 2001, 02:58
Default Non-symmetrical
  #1
Martin
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Hi

I am modelling swirling flow combined with inlet jets (turbulent). The geometry is symmetrical in one plane, but I need to model the whole geometry. Because the geometry is symmetrical in one plane I am guessing that the flow must also be symmetrical, however it is not the case. I am using an unstructured grid, but I do not believe that this has anything to do with it. Can anyone help?

Thank you
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Old   June 18, 2001, 03:31
Default Re: Non-symmetrical
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John C. Chien
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(1). Need to know more about your problem. (2). Is your geometry symmetrical? That is, can you generate your geometry by rotating a 2-D geometry through 360 degrees? (3). If the boundary condition is also 3-D axi-symmetrical, then you should be able to get axi-symmetrical solution. (there was an axi-symmetric version of the code a few years back. I don't know whether it is still available.) (4). If you run it as a 3-D problem, then there is no guarantee that the solution will be axi-symmetrical, because of the mesh, the boundary conditions, and the algorithm used. But, I would say that a symmetric solution is possible, if you do it carefully.
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Old   June 18, 2001, 04:22
Default Re: Non-symmetrical
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Martin
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Thanks for the reply. The geometry is a combustor with the external field included. There are three positions along the length of the liner with different inlet jet amounts and sizes at these positions together with a swirler. There are two symmetry planes perpendicular to each other (I said one previously). My boundary conditions are a pressure inlet and pressure outlet. My logic says that it must be symmetrical but somehow I am not getting it. I am also using about 600000 cells (external and internal) so I have a fairly fine grid.

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Old   June 18, 2001, 07:23
Default Re: Non-symmetrical
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John C. Chien
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(1). You can modify the geometry and run some coarse mesh cases, just to see how the code respond to those conditions. (2). Without the actual geometry, it is hard to know why you are not getting what you are looking for.
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Old   June 18, 2001, 10:12
Default Re: Non-symmetrical
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Chinor
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Martin,

Are you using symmetry boundary conditions at the circumferential bounds of your model?

If so, try switching to periodics. For swirling flow in a combustor, you need periodic boundaries to model the physics correctly.

Regards,

Chinor

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