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

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.

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

OK, quick question, have you used a symmetry plane? If so, then you have to double the force. Stu

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

Remember this computing task list: <Li> Lift is easy[*] Drag is hard[*] Moment is imposibble

- Michael

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

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.

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

Check your reference area value

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

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

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

Thanks to all. I obtained the results.