Originally Posted by
TheOddOne
...or a B757 on the approach at 90 tonnes but with full flap deployed? The vortices off the outboard edges of the flaps are VISCOUS! and required the a/c to be re-designated 'Heavy' in that phase of flight.
TOO
All vortices are driven by viscous fluid effects.
In terms of total vortex strength, I'd intuitively expect the clean(er) wing to be worst as flaps move the lift distribution inboard, and reduce the pressure differential at the tips - which creates the large tip generated vortices which tend to be the major component of wake vortex power.
G