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Old   November 8, 2007, 01:17
Default drag coefficient
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hsn
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Hi. I'm a new user of cfx. I have done all the tutorials of the program documentation and of coarse the one with the name of flow around a blunt body(Ahmed body). I was wandering how can I achieve to the amount of drag coefficient by the software? By the way I have searched all the documentation to find a clue on the drag coefficient but I wasn't successful. Thanks for your attention.

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Old   November 8, 2007, 04:46
Default Re: drag coefficient
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Jim
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You can use the "Expressions" tools in either pre or post to extract the force acting on your boundary conditions. You can then use this to calculate the drag coefficient.
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Old   November 10, 2007, 00:20
Default Re: drag coefficient
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hsn
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thanks Jim. I did so and now I know the amount of force acting on the body. But as you know the analyze is symmetric. Should I duplicate the calculated force for whole the body to calc the drag coefficient? hsn.

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Old   November 11, 2007, 05:48
Default Re: drag coefficient
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Glenn Horrocks
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Hi,

Yes. The forces reported in CFX-Post are for the geometry as modelled. Therefore you will need to double some variables due to symmetry.

On a separate matter, I trust you are aware that the solution to the Ahmed body at typical vehicle Reynolds numbers is not symmetric and therefore you cannot use a symmetry plane if you want an accurate answer? In fact getting accurate drag numbers on the Ahmed body is quite a challenge.

Glenn Horrocks
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