Lift and Drag Equations

Tom A · January 12, 2012, 13:11

Hi, I am having some difficulty in understanding how to calculate forces using information obtained from fluent. The lift and drag equations I am using are:

D = 1/2*density*velocity^2*A*Cd
L = 1/2*density*velocity^2*a*Cl

However there seems to be different conventions for what to use as the reference area, A. For example on the wikipedia article it lists several different reference areas like airplane it says the planform area is typically used but for submerged bodies the wetted surface area is typically used. It seems like Cd and Cl values can vary depending on the application so how does Fluent calculate Cd and Cl and how should I use them?

Tom

LuckyTran · January 13, 2012, 23:46

To my knowledge, Fluent does not calculate the drag coefficient and lift coefficients (most likely because there are too many conventions).

Fluent however can report the drag and lift forces which can then be used to calculate the drag and lift coefficients according to your definition of those terms.

You should use the drag and lift coefficients for your particular application to avoid confusion with others in your field, follow the convention rather than establish your own (unless you have a better one). Otherwise, use the definitions that you are most comfortable with. It is entirely up to you.

Check out the fluent help file or manual for detailed information. It is much more like a textbook.

January 12, 2012, 13:11	Lift and Drag Equations	#1
Tom A New Member Tom Join Date: Jan 2012 Posts: 11 Rep Power: 14	Hi, I am having some difficulty in understanding how to calculate forces using information obtained from fluent. The lift and drag equations I am using are: D = 1/2densityvelocity^2ACd L = 1/2densityvelocity^2aCl However there seems to be different conventions for what to use as the reference area, A. For example on the wikipedia article it lists several different reference areas like airplane it says the planform area is typically used but for submerged bodies the wetted surface area is typically used. It seems like Cd and Cl values can vary depending on the application so how does Fluent calculate Cd and Cl and how should I use them? Tom

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Lift and Drag ???	Yogibear	STAR-CCM+	5	November 2, 2023 17:14
How does FLUENT calculate lift and drag?	xTamx420	FLUENT	0	May 30, 2011 13:35
Lift and Drag Monitor Point Values Converging to Zero	Josh	CFX	24	May 9, 2011 10:38
Correct lift but wrong pressure drag - possible?	zx	Main CFD Forum	4	July 27, 2007 23:38
Fluid mechanics / drag & lift	Jamcam	Main CFD Forum	0	October 31, 2002 04:39

January 13, 2012, 23:46		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,673 Rep Power: 65	To my knowledge, Fluent does not calculate the drag coefficient and lift coefficients (most likely because there are too many conventions). Fluent however can report the drag and lift forces which can then be used to calculate the drag and lift coefficients according to your definition of those terms. You should use the drag and lift coefficients for your particular application to avoid confusion with others in your field, follow the convention rather than establish your own (unless you have a better one). Otherwise, use the definitions that you are most comfortable with. It is entirely up to you. Check out the fluent help file or manual for detailed information. It is much more like a textbook.