Quote:
Originally Posted by vortex
A series of vortex generators do energize the boundary layer but by the energy imparted to it by the VG blade and less from the higher speed outer boundary layer. Inside the vortex filament is a very low pressure core which keeps it attracted to nearby surfaces. You can visualize the low pressure by the way wing tip vortices condense vapor on a humid day. VG's are not free though as it requires a continual supply of (propulsive) energy to sustain the pressure deficit residing in the cores. The benefit you buy with that cost is greater resistance to catastrophic flow separation and (wing) stall.
It can be argued that the gyroscopic effect of the twisting air mass might tend to stabilize the filaments thereby reducing sensitivity to turbulence as the stream-tube filament row is passed over surfaces or even an open area such as a tractor-trailer gap. This is harder to visualize in air without introducing smoke, but witness the stability of the linked toroidal vortex in water and apply that intuition to a short straight vortex in air. |
I'm okay with the 2-D wing,under flight conditions, at large angle-of-attack,as there is always a flap,aileron,trim-tab,elevator, engine nacelle,or tailcone section behind the VG, for which the flow can reattach.Ludwig Prandtl was demonstrating attached flow on wings at up 40-degrees AOA in the 1920s.
Without a reversed-step box cavity or 'steep' boat tail behind the trailer,there would be nothing for flow to reattach to.Without that,essentially,there cannot be any pressure recovery of attached,decelerated flow.So we're stuck with the same base pressure,and same pressure drag.
Can we dig even deeper?