[jaywee]

I know the drag always aligns with the freestream direction, so it is quite easy to compute drag by:
drag = <total force vector> * <unit vector of freestream direction>


However, the lift force's direction is not obvious. I think the lift formula should be
<lift vector> = <total force vector> - drag * <unit vector of freestream direction>
then the magnitude of lift could be got by

lift = sqrt(<lift vector> * <lift vector>), which is a complex formula.


But in the SU2's code, the lift formula is very simple: (click here to check source code: https://github.com/su2code/SU2/blob/...Base.inl#L1979)

InvCoeff.CL[iMarker] = -ForceInviscid[0] * sin(Alpha) + ForceInviscid[2] * cos(Alpha);


It looks strange to me, b/c lift has no dependence on Beta. Anyone could help to explain or post some reference link? Thanks.

[CleverBoy]

As a graduate student I am really not sure about this but I guess they are taking normal and axial force's coefficients and using them on the lift and drag calculations. When I first saw the eqns. in code I tought they reminded me of something and found them on the Anderson's Fundamentals of Aerodynamics book. I attached 2 pictures as reference. In my opinion, they are not as easy as they look, at first glance at least you get to used to them in time.

[pcg]

The result of <force vector> - drag * <drag direction> is not the lift vector, but rather lift + sideforce