One 'wild idea' is to get some small diameter, semi-rigid, plastic tubing and form it to build a boundary layer, suction manifold. The idea is to to suck the boundary layer down and possibly using this approach to keep the boundary layer attached. The challenge is how to build it.
At the hardware store, I can find:
- small diameter copper tubing
- polyethelyne plastic tubing
- PVC tubing - generally no larger than 1/2 inch
- small diameter aluminum tubing
The copper tubing is a little expensive but remains malleable. My concern is that over time, a small gap might close as stress and strain over the 5-6 ft. causes it to flex. To work, the gap needs to remain.
Polyethelyne plastic tubing, the hard, somewhat opaque stuff, is also something that I feel is too flexible. This isn't the vinyl, flex stuff, but still, it is less likely to 'take a hit' and stay closed as copper would.
PVC tubing, as small as possible, looks to be a best answer. Filled with sand and heated, it should 'mold' to fit the rear window curve. Once cooled, it should quickly hold its shape and conform to the upper glass junction. Then using a tapered, balsa fillet and duct tape, flair it right into the glass. A Drimel tool can cut a thin, length-wise gap. The ends can use standard PVC fittings to attach to a vacuum pump. That leaves just the problem of finding a vacuum pump, an air horn pump comes to mind.
I think aluminum tubing might also be used as an alternative to PVC tubing. It should not be as malleable as copper and possibly closer to PVC. Now one 'wild idea' would be to setup a pair of rollers that form an angle and try to reshape the aluminum tube into more of an aerodynamic shape. The advantage is a larger cross-section for the manifold space. Done properly, the ends should still remain circular for standard tubing.
Both vortex generators and vacuum pumps take energy. The vortex generator induces circulation and the vacuum pump needs power. In theory, these energy losses are much less than the improved pressure thrust. But this may be difficult to quantify ... something I'll be thinking about.
Bob Wilson