ernie,
Probably much the same thing.
A boundary layer going turbulent can cause a lot of low frequency noise and/or vibration, and even if not really audible, it can still make the pax uncomfortable, and possibly even sick.
Any photos of the 'vortice generator'?
fnp90,
Very clear drawings! Thanks.
Looking at your photo again, what aircraft is it? A340?
Are the two "dotted lines" on the wing, in line with the vortex and the nacelle, also two rows of vortex generators?
CJ