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how to calculate cd -- drag coefficient??????

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Old   April 6, 2006, 03:12
Default how to calculate cd -- drag coefficient??????
  #1
vijesh joshi
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Hi, I have simulated the flow over an aerospace vehicle. Now I can get the drag force on the surface of the vehicle(with the help of readymade options that are available in CFX-post). I know that, cd = drag force / (dynamic pre * reference area). Whatever the cd that I have obtained is being half of the exact value. I am not getting the mistake. Plz help. Thank you.
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Old   April 6, 2006, 05:55
Default Re: how to calculate cd -- drag coefficient??????
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Stuman
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OK, quick question, have you used a symmetry plane? If so, then you have to double the force. Stu
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Old   April 6, 2006, 08:01
Default Re: how to calculate cd -- drag coefficient??????
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Michael Bo Hansen
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Remember this computing task list: <Li> Lift is easy[*] Drag is hard[*] Moment is imposibble

- Michael
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Old   April 6, 2006, 08:17
Default Re: how to calculate cd -- drag coefficient??????
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PetrK
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Hi I have obtained for a 3D wing a good results even for Cm Coeff. However its difficult to compare it to other methods since every numeric method has serious problems with moments.
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Old   April 6, 2006, 08:18
Default Re: how to calculate cd -- drag coefficient??????
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PetrK
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Check your reference area value
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Old   April 6, 2006, 19:07
Default Re: how to calculate cd -- drag coefficient??????
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Glenn Horrocks
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Hi,

Yes, check your reference area; but also most people calculate drag from Cd = D / (A * .5 * rho * V^2) (http://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html) and that has a factor of 2 in it. If you left it out you would be out by exact 2! Maybe that's it.

Regards, Glenn Horrocks
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Old   April 6, 2006, 23:35
Default Re: how to calculate cd -- drag coefficient??????
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vijesh
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Thanks to all. I obtained the results.
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