Mercedes F-Duct scenarios analyzed on how they think it works. The title does end in a question mark.
A wing of a single element which we see as the flow separates from the wing. This is BAD.
Wing 2 FLAT (No F-Duct. Well curve. Poor in straight)
With a wing of two elements, the flow passes through the slot to prevent separation of fluid, keeping the laminar regime. More downforce. This is GOOD in curves and on straight BAD
2012 MERCEDES WING
When the air blows in the duct slot, it disrupts the laminar air flow, causing turbulence behind the spoiler, the stall, and permits the loss of resistance(drag). LESS RESISTANCE. This is good in straights and bad for curves.
These images are from a pretty good analysis. It can be found here at the
F1 Writers website. It is in Espanol but if you don't understand Spanish Google translate or Bing Translator work well enough for you to get the jist.