Force coefficient Cf
 

Previously I calculated cfx and cfy as

Cfx=Fx/(0.5*rho*vz^2)*A
Cfy=Fy/(0.5*rho*vz^2)*A
where A is projected area in the direction of wind


But in some paper they are taking Ax= Projected area normal to the direction of wind for cfx and Ay=Projected area parrallel to the direction of wind


which one is correct
?

You can calculate them following the convention you want to adopt. I mean, what is in the denominator (\rho v^2 A) is a simple number, dimensionally consistent with Fx to make their ratio dimensionless.

Usually A is chosen such as it is the area that the flow "views". But you can decompose the speed vector into its components (v_x,v_y) and calculate the areas A_x A_y respectively as well.

Hello,

There's no convention as to how the reference area is chosen. Contrary to the above post, the reference area isn't chosen based on what the flow sees. It depends on what kind of work you are doing and the convention followed in that area.

For example, in my work with airfoils, the literature that I consult with to check the results, use the chord length * span as the reference area. Though you are free to use what you want to non-dimensionalize your data.

I would suggest that you look at the literature related to your work and follow the convention that it follows. This will make is easier for you comapre your results with the published data.