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

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Old   October 10, 2022, 23:27
Question How to explain the lift force in SU2's source code?
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Jay Wee
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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:

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.
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Old   October 22, 2022, 12:59
Ercan Umut
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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.
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File Type: jpeg anderson.jpeg (116.6 KB, 44 views)

Last edited by CleverBoy; October 22, 2022 at 16:02.
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Old   October 23, 2022, 20:38
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Pedro Gomes
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The result of <force vector> - drag * <drag direction> is not the lift vector, but rather lift + sideforce
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lift, source code, su2

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