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An aerodynamic base drag reduction apparatus and method for bluff bodies, such as tractor-trailer trucks, utilizing a pair of lift surfaces extending to lift surface tips and located alongside the bluff body such as on opposing left and right side surfaces. In a flowstream substantially parallel to

An aerodynamic base drag reduction apparatus and method for bluff bodies, such as tractor-trailer trucks, utilizing a pair of lift surfaces extending to lift surface tips and located alongside the bluff body such as on opposing left and right side surfaces. In a flowstream substantially parallel to the longitudinal centerline of the bluff body, the pair of lift surfaces generate a pair of counter-rotating trailing vortices which confluence together in the wake of the bluff body in a direction orthogonal to the flowstream. The confluence draws or otherwise turns the flowstream, such as the flowstream passing over a top surface of the bluff body, in and around behind a trailing end of the bluff body to raise the pressure on a base surface at the trailing end and thereby reduce the aerodynamic base drag.

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1. A method of reducing aerodynamic base drag of a bluff body vehicle adjacent a ground plane in a flowstream substantially parallel to a longitudinal centerline of the bluff body vehicle, said bluff body vehicle having a leading end, a trailing end, a top surface, opposing left and right side surfa

1. A method of reducing aerodynamic base drag of a bluff body vehicle adjacent a ground plane in a flowstream substantially parallel to a longitudinal centerline of the bluff body vehicle, said bluff body vehicle having a leading end, a trailing end, a top surface, opposing left and right side surfaces, and a base surface at the trailing end substantially normal to the longitudinal centerline of the bluff body, said method comprising:generating a pair of counter-rotating vortices from alongside the bluff body upstream of the base surface to confluence downstream in the wake of the vehicle in a direction substantially orthogonal to the flowstream, whereby said confluence draws the flowstream in and around behind the trailing end to raise the pressure on the base surface and reduce the aerodynamic base drag.2. The method of claim 1,wherein a pair of lift surfaces extending to lift surface tips are utilized to induce generation of the pair of counter-rotating vortices as trailing vortices.3. The method of claim 2,wherein the pair of lift surfaces extend in substantially opposite directions from each other.4. The method of claim 2,further comprising utilizing at least one additional pair of said lift surfaces to induce generation of a corresponding number of additional pairs of counter-rotating trailing vortices.5. The method of claim 4,wherein the pairs of counter-rotating trailing vortices are generated to confluence in the same direction.6. The method of claim 1,wherein the pair of counter-rotating vortices are generated from alongside the left and right sides of the vehicle to confluence downstream in the wake of the vehicle in a downward direction to the flowstream, whereby said confluence draws the flowstream passing over the top surface down and around behind the trailing end to raise the pressure on the base surface and reduce the aerodynamic base drag.7. The method of claim 6,wherein a pair of lift surfaces extending to lift surface tips are utilized to induce generation of the pair of counter-rotating vortices as trailing vortices.8. The method of claim 7,wherein the pair of lift surfaces extend in substantially opposite directions from each other.9. The method of claim 7,further comprising utilizing at least one additional pair of said lift surfaces to induce generation of a corresponding number of additional pairs of counter-rotating trailing vortices.10. The method of claim 9,wherein the pairs of counter-rotating trailing vortices are generated to confluence in the same direction.11. The method of claim 1,further comprising generating at least one additional pair of said counter-rotating vortices.12. The method of claim 11,wherein the pairs of counter-rotating vortices are generated to confluence in the same direction.13. The method of claim 1,wherein the bluff body vehicle is a tractor-trailer.14. A method of reducing aerodynamic base drag of a bluff body vehicle moving in close proximity to a ground plane in a flowstream substantially parallel to a longitudinal centerline of the bluff body, said bluff body having a base surface at a trailing end thereof, said method comprising:providing alongside the vehicle upstream of the base surface a pair of lift surfaces extending to lift surface tips, said pair of lift surfaces capable of inducing generation of a pair of counter-rotating trailing vortices when in the flowstream, and said lift surface tips substantially near the bluff body to confluence the vortices downstream in the wake of the vehicle in a direction substantially orthogonal to the flowstream, wherein said confluence draws the flowstream in and around behind the trailing end to raise the pressure on the base surface and reduce the aerodynamic base drag.15. The method of claim 14,wherein the pair of lift surfaces are provided on left and right sides of the vehicle upstream of the base to confluence downstream in the wake of the vehicle, with said downwash confluence drawing an upper flow above the vehicle down and around behind the base to raise the pressure on the base and reduce the aerodynamic base drag.16. The method of claim 14,wherein the pair of lift surfaces extend in substantially opposite directions from each other.17. The method of claim 14,further comprising providing at least one additional pair of said lift surfaces to generate a corresponding number of additional pairs of counter-rotating trailing vortices.18. The method of claim 17,wherein the pairs of counter-rotating trailing vortices are generated to confluence in the same direction.19. The method of claim 14,wherein the bluff body vehicle is a tractor-trailer.20. A method of reducing aerodynamic drag of a bluff body in a flowstream substantially parallel to the longitudinal centerline of the bluff body, said method comprising:generating at least one pair of counter-rotating vortices alongside the bluff body to induce downstream confluence of said vortices in the wake of the bluff body in a direction substantially orthogonal to the flowstream, whereby the confluence draws the flowstream down and around a trailing end of the bluff body to raise the pressure in a recirculation zone thereof and reduce the aerodynamic base drag.