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Good example of VG use. However, for the ecomodder, one thing is missed. VG's impart energy, useable energy, that we can use to our advantage. In consideration of the relatively slow speeds we drive compared to the speeds of aircraft, VG placement and design will need to be somewhat different. I.e., a glider can effectively use the Z strips because the wings are designed around laminar flow, a boundary layer so close to the wing that those 1/16 or less bumps are beneficial. On a car however, Z strips are all but useless because cars are not designed with laminar flow in mind but flow more so related to the old cumbersome wings you see on 30 plus year old airplanes. Back to imparting energy. Knowing most all cars and trucks have flow separation at the rear, beyond that of the boot, tailgate, trunk, or hatch, we can now take this energy imparting device and strategically place it to "create" the boat tail the adds to aerodynamic efficiency. Look at the post below with the car and arrows representing drag, by placing the VG's at the very rear, tuff test to find where flow starts loosing energy, of vehicle. By placing the VG's here, we lengthen the effective (aerodynamically perceived) rear of the car thereby decreasing considerably the deep low pressure area created. So, when you think of VG's, don't think of the minuscule effects of air over roof and trying to straighten them but rather think of VG's as you would a permanent mod on the rear or anywhere you have the low pressure areas created. In contrast, VG's are not hard mods but merely imparting controlled energy into the air. Therefore if we are generating energy from the air, some of that generation is taking from the force to move the vehicle and therefore hard mods will always out perform VG's, but for quick, inexpensive flow control, with $$$ benefits, VG's are the way to go.
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