[lunarhighway]

the gist of this post is
"can you box in turbulence, as an alternatice to a smooth fairing"

i initially came to this while reading a wikipedia article on a defuser.
it seems to sugest the real merit of defuses is to allow air to chance in speed and pressure (at the rear of a car) in a controlled way, rather then to become turbulent. the later struck me as important.

Most cars these days have bumpers wich extend below the lowest visual part of the car, such as the spare wheel well and the exhaust system.
for a long time i thought this was just to hide these ugly parts from view, and was only adding drag by trapping the air behind. but than it struck me this might also contain the turbulence and uneven flow caused by these parts and allow the remainder to the air to decelerate in a more controlled way, thus decreasing overall drag, a bit the same as an airdam in reverse, or the pickup tailgate test upside down(wich showes up is better then down). is this still makeing sence?

than i got thinking further that if this is correct than any part of a cars (under) body that ideally should be faired over, but can't for practical reasons, might benefit from "boxing in", being surounded with small dams, wich create an air cussion around the part over wich smooth(er) airflow can exist.

another example would be the use of dams in front of the wheels (as seen on production cars) in favour of the aerodynamicly superior full fairing, wich isn't practicly possible, but also might cause lift or instability in crosswinds (something autospeed suspected in their "test" of such fairings, and wich was the reason for them to abandone the idea despite fuelsaveings).

so what about a "compound dam" a series on dams of increasing size placed at a certain distance of eachother in front of the wheels, the contours of wich approach that of an "ideal fairing". each fairing would have a low pressure area behind it, wich might create downforce and sidewinds would be able to pass trough the fairing wich perhaps helps stabilty further. as each fairing could be set up to flew the whole unit is practically invunerable to curb impacts, wich make full fairings impossible.

is my reasoning sound or am i mixing things up?