Wake vortices are made less detectable or reduced in their effect on
nearby vehicles by re-orientation of vorticity about an axis in the
direction of vehicle motion to transverse vorticity interacting with the
longitudinal vorticity. The re-orientation may be by a flapping foil, and
arrangements of a plurality of foils moving toward or from each other may
be used. Alternatively, fluid may be injected longitudinally between
opposite surfaces each having a port so that selective suction through
the ports alternately attaches the fluid to the surfaces to deflect the
fluid from the longitudinal direction and generate transverse vortices.
Oppositely rotating vortices may be formed by separators extendable from
each surface to engage the deflected fluid, and extension of the
separators may be varied to control vortex trajectory. The transverse
vortices may be intermittent, selected for speed, or made asymmetric for
maneuvering.