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

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 April 6, 2006, 03:12 how to calculate cd -- drag coefficient?????? #1 vijesh joshi Guest   Posts: n/a 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.

 April 6, 2006, 05:55 Re: how to calculate cd -- drag coefficient?????? #2 Stuman Guest   Posts: n/a OK, quick question, have you used a symmetry plane? If so, then you have to double the force. Stu

 April 6, 2006, 08:01 Re: how to calculate cd -- drag coefficient?????? #3 Michael Bo Hansen Guest   Posts: n/a Remember this computing task list:
• Lift is easy[*] Drag is hard[*] Moment is imposibble - Michael

•  April 6, 2006, 08:17 Re: how to calculate cd -- drag coefficient?????? #4 PetrK Guest   Posts: n/a 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.

 April 6, 2006, 08:18 Re: how to calculate cd -- drag coefficient?????? #5 PetrK Guest   Posts: n/a Check your reference area value

 April 6, 2006, 19:07 Re: how to calculate cd -- drag coefficient?????? #6 Glenn Horrocks Guest   Posts: n/a 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

 April 6, 2006, 23:35 Re: how to calculate cd -- drag coefficient?????? #7 vijesh Guest   Posts: n/a Thanks to all. I obtained the results.

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