So in the past I've discounted active flow control as something just too complicated to implement into an already existing car....
But with my kamm project, I've got some renewed interests....
Things like VG's, zigzag shapes (also a VG), lips, etc. are passive methods of controlling flow.
Active flow control is basically perturbing flow with your own controlled flow... You can do this with vacuum (sucking), pressure (blowing) or mechanically with things like fluttering spoilers and such.
On aircraft wings, that looks something like this
But on a car.... It's a little different
So the C-Class merc takes in fast moving air under the car, and ejects it out of slits in the tail light lenses. The C-Class has a cD of .27 - probably not all tail lights... but they did spend the R&D time and money and then more time and money to make it... One would be led to believe that they decided gains were to be had....
The idea is redirect flow behind and away from the car, rather than wrapping around and doing nasty things against the car.
Here's a better photo showing the little slits on the outside edges
Just thought I'd share.... As far as how I personally would implement active flow control... Not sure yet, but I'm experimenting
