Quote:
Originally Posted by s2man
I don't think you want to deflect air behind your minivan with the 1/4 noodles. The best method is to get the air flow to separate cleanly from your vehicle, either via a sharp lip, ala Kamm back, or with vortex generators. Speaking of that, does anyone know where I can get some wedge shaped rubber molding which I can glue around the back end of my car to create said lip.
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I do indeed, clean separation is good for clean shapes. Many modern wagons have a sharp lip separation at the roof, because they have a kind of "tumblehome" turning in of the sides at the top rear that shapes the flow differently than older and more slabsided vehicles. I am aiming to make a virtual boattail, a virtual Kammback behind the minivan. Vortex generators don't really separate the flow cleanly, they just enable easier vortex shedding, of smaller vortices as compared to large vortices attaching to the back of the vehicle.
That's really what throws some vehicles around on the highway when others pass, they've got two huge vortexes behind them, left hand and right hand, and the passing vehicle will collapse the vortex on one side with it's bow wave and the other vortex will be doing as much pulling you around as the bow wave is pushing you around, due to the pressure now being uneven. At high speed these vortices start flopping around causing instability. It's probably flopping large scale vortices that will start a boxy trailer snaking on a tow.
A speeding sphere for example still does better for base drag than a speeding cube, despite the fact that the cube has clean edge separation.
I don't think the aero on most vehicles was developed very 3 dimensionally up until the late 90s, or 2000s. Anyway, you don't want to stick these on the trunk lip of a Neon or a Saturn sedan, but a minivan design laid out in ~82 for introduction for the '84 model year is something different.
GasSavers_RoadWarrior 
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