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-   -   How can I calculate force for lift coefficient and drag coefficient ? (https://www.cfd-online.com/Forums/cfx/155549-how-can-i-calculate-force-lift-coefficient-drag-coefficient.html)

gemxx July 2, 2015 19:47

How can I calculate force for lift coefficient and drag coefficient ?
 
After I had searched this matter on internet for hours, I had to write here to find a way to solve this problem. Because I have to prepare CL ve CD graphics in a short time for my project. (about an airfoil)

(I'm sorry for spending your time )

I tried to read data related to force on CFX post, but I found illogical values at every turn.

I`m looking force values by using "Function Calculator" on CFX Post. There are many options and I tried all of them, however I couldn`t find available CL avd CD coefficients.

I selected ;
for Function as "areaint" and for Location as "blade" for variable "pressure".
for Function as "areave" and for Location as "blade" for variable "pressure".
for Function as "areaint" and for Location as "blade" for variable " total pressure".
for Function as "areave" and for Location as "blade" for variable " total pressure".
for Function as "force" and for Location as "blade" for direction " global X and Global Y seperately".

Furthermore, I tried to read force value on CFX Solver Manager by using monitors but I found illogical values again.

Do you know another ways which you can advise me ? ( my y plus value is about 25-30 )

Thomas MADELEINE July 3, 2015 08:01

well you can easily determine the Cx and the Cz of your airfoil by the simple equation :
Fx = 0.5 x density x Area x Velocity^2 x Cx
Fz = 0.5 x density x Area x Velocity^2 x Cz

you have the force_x@blade function, area()@blade, massFlowAve(Density)@Inlet, massFlowAve(Velocity)@Inlet...

then you cant calculate your coefficients.

gemxx July 3, 2015 17:31

Quote:

Originally Posted by Thomas MADELEINE (Post 553494)
well you can easily determine the Cx and the Cz of your airfoil by the simple equation :
Fx = 0.5 x density x Area x Velocity^2 x Cx
Fz = 0.5 x density x Area x Velocity^2 x Cz

you have the force_x@blade function, area()@blade, massFlowAve(Density)@Inlet, massFlowAve(Velocity)@Inlet...

then you cant calculate your coefficients.

I can calculate the force now but the values are very small. For example, although the exact value must be 4,6 N for lift force at 5 degrees, my force value is 0,00146 N.
Do you think what the reason may be about this?

The analysis is steady state and air speed is 4 m/s.

ghorrocks July 4, 2015 08:37

Are you sure your simulation is accurate?

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F


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