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Old   February 18, 2009, 07:52
Default Forces in Symmetry
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Matt
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Hi,

I'm wanting to calculate the resultant force on a body. The body is axi-symmetric in 2 planes; hence, at a zero angle of attack, two of the component forces should equal zero. Therefore, one force on the body can be found; that is in the direction of the fluid.

When I do the computation for the whole body (not using a symmetry plane), two of the component forces are zero and the one that's left (in the direction of flow) gives me the force on the body... which is what I want.

So, here's the problem: When using a symmetry plane, to reduce computation time, the forces do not seem to appreciate the symmetry I have set. Flow visualisation is fine with the symmetry; just force calculation does not match up. I get a huge force in the direction normal to the symmetry plane. I think it is calculating a force on the body in this direction, and not appreciating that an equal and opposite force should be on the other side of the symmetry plane.

I may not have a setting enabled or perhaps symmetry planes are not built for this... Any help would be much appreciated.

Thanks in advance,

Matt
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Old   February 18, 2009, 17:40
Default Re: Forces in Symmetry
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Glenn Horrocks
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Hi,

The force in the simulation with the symmetry planes is the force acting on the simulated section. It does not take into account symmetry. This means you are likely to get large larges which in the true geometry are cancelled out. So you can ignore force components perpendicular to a symmetry plane for the total force on the body.

Glenn Horrocks
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Old   February 25, 2009, 06:41
Default Re: Forces in Symmetry
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Matt
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Hi Glenn,

Thanks for your help. Much appreciated.

Matt
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