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hsn November 8, 2007 02:17

drag coefficient
 
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.


Jim November 8, 2007 05:46

Re: drag coefficient
 
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.

hsn November 10, 2007 01:20

Re: drag coefficient
 
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.


Glenn Horrocks November 11, 2007 06:48

Re: drag coefficient
 
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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