Originally posted by undersquare
My bet is that some of the air is going straight through the sidepods to the rear, not doing any cooling, to feed the rear aero.
That might be the case, but I think it's unlikely. Air is a lot like electricity, it takes the path of least resistance. If you have a pipe and split it 50/50 halfway down, with a clear path on one side and a radiator on the other, most of the air would take the clear path - working out a balanced solution for split ducts is pretty complicated, and was a minor part of the reason that F1 cars moved away from the bifurcated sidepod radiator/engine intakes we saw in the 80's to the overhead engine intakes we have today.
I think it's more likely that these shrouded exhaust ducts are the new version of the chimneys that were standard in F1 for so long. In this implementation, the hot air from the radiators and the hot air from the exhausts is being mixed and used to drive the rear wing, aided by the clever design of the toed-in wing supports, steering the flow to the bottom . The effect is rather like having a jet engine blowing over the bottom of the wing, speeding the airflow.
The really interesting thing we've seen today is the notched floor. With the heavily waisted sidepods we've seen this year, some parts of the area above the floor behind the sidepod have likely become somewhat marginal in terms of downforce generation, possibly even to the point of generating lift. Adding a notch here and allowing the flow to mix could cancel out this effect nicely, especially if you have a powerful diffuser acting on the center of the undertray.
Although it appears to be a simple notch, it's actually somewhat more complicated - and clever. If you look, the rear of the 'notch' is higher than the front, acting as a tiny splitter and guiding part of the sidepod flow under the floor. A small flip-up has been placed just in front of the tire - in effect, turning the raised part of the floor behind the notch into a small winglet. I'm not sure what the FIA will say about this, but it appears to be legal - the raised part of the floor acting as a splitter counts as being part of the 'step plane' allowed 50mm above the main reference plane and isn't counted as part of upper bodywork.