# How to explain the lift force in SU2's source code?

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 October 10, 2022, 23:27 How to explain the lift force in SU2's source code? #1 New Member   Jay Wee Join Date: Oct 2022 Posts: 6 Rep Power: 3 I know the drag always aligns with the freestream direction, so it is quite easy to compute drag by: drag = * However, the lift force's direction is not obvious. I think the lift formula should be = - drag * then the magnitude of lift could be got by lift = sqrt( * ), 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. Last edited by jaywee; October 11, 2022 at 08:17.

October 22, 2022, 12:59
#2
Member

Ercan Umut
Join Date: Aug 2022
Posts: 44
Rep Power: 3
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.
Attached Images
 anderson2.jpeg (57.3 KB, 49 views) anderson.jpeg (116.6 KB, 44 views)

Last edited by CleverBoy; October 22, 2022 at 16:02.

 October 23, 2022, 20:38 #3 Senior Member   Pedro Gomes Join Date: Dec 2017 Posts: 466 Rep Power: 13 The result of - drag * is not the lift vector, but rather lift + sideforce

 Tags lift, source code, su2