Hi,
One question:
when I get the fluid forces px,py,pz,vx,vy,vz to compute actual lift I’ve done vy-py, but to compute the lift coefficient for a 3D problem, namely Cl = lift/(0.5 rho v^2 * Area), is there a simple way to find the area of the surface (wing) via pyFR or python scripts where the integration of this forces has been done such that one can normalize correctly the lift force?
This is not something which PyFR can easily calculate and is often up for debate. As an example, for a wing, there is the choice between the wetted area and the planform area. Both are widely used.
Regards, Freddie.
Regarding this question, I want to know if my assumption is correct:
to compute lift coefficient with pyFR I have to do:
(vy + py) / ( 0.5 rho v*v * Area)
(previously I said I was doing vy - py)
I have to sum both viscous stresses and pressure force because in the solver you already compute the scalar product between the surface outward normal to airfoil and the unit versor which defines the lift direction (y in this case).
Is this true?
Because aerodynamics formula generally refers to
but the dot product has to be computed to account for both pressure and suction side
@fdw Am I correct on this?
yep, this is correct.
Thanks a lot for the feedback!
Hello, in the example you mentioned, “for a wing, there is the choice between the wetted area and the planform area. Both are widely used.”
I have some confusion because in some literature, the term “Cl” appears so naturally that it’s not specified whether it’s based on the wetted area or the planform area, which has been troubling me. Do you have any advice?
My method of calculating the area involves importing my wing into CAD software like CATIA, which has surface area measurement features that allow me to measure the upper surface area and lower surface area of my wing, and then I add these two areas together. I have no idea if what I’m doing is correct because I don’t know how to calculate the area of complex surfaces accurately.
While this question may not be directly related to pyFR, I would appreciate your reply.
Regards.
Oh, I’ve also heard about the projected area of a wing.
I’m not sure which one is correct, whether it’s the projection of the wing or the sum of the upper surface area and lower surface area.
I’m quite uncertain because the projected area of a wing may be roughly only half of the combined upper and lower surface areas, which could lead to a significant error.
I’d appreciate your insights.
Regards.