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-   -   Lift and Drag Equations (http://www.cfd-online.com/Forums/fluent/96116-lift-drag-equations.html)

Tom A January 12, 2012 14:11

Lift and Drag Equations
 
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 14, 2012 00:46

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.


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