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Mar3-12, 10:35 PM
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Quote Quote by RandomGuy88 View Post
If the boundary layer were completely turbulent on the airfoil this could dramatically change the lift because the displacement thickness is much larger and this alters the effective shape of the body. This usually decambers the airfoil and reduces the lift.
Let's not exaggerate. It will almost never "dramatically" change the lift. Even a turbulent boundary layer on a typical airfoil is only often several millimeters thick. The displacement thickness is not that much to begin with so it won't be that dramatic of an effect most of the time. Of course there are always exceptions, but in general the increased turbulent displacement thickness is not that dramatic.

Quote Quote by RandomGuy88 View Post
I believe a similar thing happens on swept wing that experience attachment line transition. In this case the boundary layer almost immediately becomes turbulent at the attachment line and creates an excessively thick boundary layer dramatically reducing the lift.
That is definitely true of attachment line contamination, but again it isn't the huge effect you seem to be implying. The turbulence is much more important due to its effect on drag than lift.