Mclaren's rear wing passed tech today in Bahrein and is now legal, look for other teams to follow suit if it proves successful.
This video from Gazzetta Dello Sport explains the basic concept. The "shark fin" encloses a hollow section channeling air from the intake to narrow slits along the top element of the wing. In the very fast sections this flow reaches a critical speed at which the turbulence created detaches the air from the wing causing it to stall and lose downforce and therefore, drag. On a track like Bahrain which with the new added sections is essentially long straights joined by a go kart track, you can see the benefits of such a solution.
There was some suspicion that the flow in this channel could be controlled by the driver and that it would therefore constitute a movable device not allowed by the regulations (as opposed to the front flaps). It's not clear if that is the case or not but whatever it is, it's legal, at least for this first race.
UPDATE: the snorkel mentioned in the comments appears to be true making this explanation even more simplistic! ...amazing, add another duty for the drivers now they have to play, as mentioned, a formula 1 flute!
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