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

April 6, 2006, 04:12

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, 06:55

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

April 6, 2006, 09:01

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

- Michael

April 6, 2006, 09:17

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, 09:18

Check your reference area value

April 6, 2006, 20:07

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 7, 2006, 00:35

Thanks to all. I obtained the results.

April 6, 2006, 04:12	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, 06:55	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, 09:01	Re: how to calculate cd -- drag coefficient??????	#3
Michael Bo Hansen Guest Posts: n/a	Remember this computing task list: <Li> Lift is easy[] Drag is hard[] Moment is imposibble - Michael

April 6, 2006, 09:17	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, 09:18	Re: how to calculate cd -- drag coefficient??????	#5
PetrK Guest Posts: n/a	Check your reference area value

April 6, 2006, 20:07	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 7, 2006, 00:35	Re: how to calculate cd -- drag coefficient??????	#7
vijesh Guest Posts: n/a	Thanks to all. I obtained the results.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Drag Coefficient Convergence Problem	John	FLUENT	18	June 24, 2023 10:22
Ahmed Body Coefficient of Drag how to calculate?	ha85	FLUENT	1	December 19, 2009 13:17
Drag coefficient for parcels in dieselFoam	sebastian_vogl	OpenFOAM Running, Solving & CFD	5	December 31, 2008 13:19
Automotive test case	vinz	OpenFOAM Running, Solving & CFD	98	October 27, 2008 09:43
how can i calculate the lift and drag coefficient	yujun	Main CFD Forum	5	January 23, 2003 16:16