Per wrote:These zig-zagged tapes you are referring to cause the boundary layer to become turbulent which postpones flow separation (the same reason why dimpled golf balls have lower drag than perfectly round ones).
Right. My fault .
Than maybe it works like self-adjusting boundary thickness control device (turbulator) described in this paper ?: http://www.lange-aviation.com/pdf/in_the_press/soaring-02_01.pdf
Funny thing: most of the research was done in Delft
Could it be possible to let the air leave the slots at a greater velocity than the surrounding flow? And thus lower the pressure at the bottom of the wing and create more downforce? I think there's no way you can get some proper flow through such narrow ducts, but who knows... If it is possible, this would increase downforce but also drag (like sending air through a duct usually does).
Pressure difference means acceleration, but i doubt this amount of air can have any significant impact on the total downforce, other then by controlling separation or laminar to turbulent transition point.
Also, maybe the duct chokes above a certain velocity which would mean the drag penalty disappears (which explains the use of the term 'F duct').
At top speeds around 100m/s air compression starts to be a factor, so i would say yes to chocking theory - even more so taking into account that, judging by the pictures, outlet slits area seems to be much smaller than inlet.