Quote:
Originally Posted by j-c-c
Well two points combined here makes me wonder. The Bubble at the front windshield base helps smooth airflow over the car. So why is it the drivable car they use that location for engine air intake to reduce that bubble?
I find it hard to believe any power gain from higher intake pressures offsets aero losses/drag/DF from reducing that useful bubble.
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1) the 'bubble' dates to the ( Ludwig )Prandtl 'surface of discontinuity' reported on by Frederick Lanchester in 1907. Air will 'figure out' how to get around an object which is attacking it by forming a perfectly streamlined phantom shape ahead of the actual structure ( seen in all wind tunnel smoke flow, and water-table flow images).
2) The flow attachment is due to a 'critical radius' at the leading edge at the windshield header and A-pillars.
3) On NASCAR racers, if you relied on the forward stagnation point for engine air you'd be screwed during a two-car, or three-car draft. By moving the combustion-air inlet to the cowl 'bubble', you get some fraction of stagnation pressure, and it's further away from the track surface, which might be 140-F on a summer race day, providing higher charge density than at the radiator inlet.
4) And even at 220-mph at Daytona, ram-air isn't as impressive as one might think. The volume of air which the engine is ingesting from this 'bubble' is miniscule compared to volume available from the oncoming flow.
This stagnation bubble travels along with the car, and the kinetic energy robbed from the free-stream to maintain it isn't remarkable, compared to the wake.