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Old 12-23-2020, 04:42 PM   #28 (permalink)
aerohead
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how diffusers work

Quote:
Originally Posted by JulianEdgar View Post
I'd already made it clear what the incorrect information was, but here it is again. You wrote:

That's my take, at least on supercars. Ferrari has flaps that lower to a less radical angle on the straights, where cornering force isn't as important, then on approach to turns, the flaps lift, increasing the ramp angle, allowing low base pressure to communicate under the diffuser. Online, there are photographs of a Lamborghini configured for this and the tufts indicate forwards airflow down and under the car, heading for the suction peak at the venturi.

Low base pressure doesn't communicate under the diffuser - that's not how diffusers work. It's similar to the idea that you have that lift is caused only by separation on the upper surfaces of cars.
I hear what you're saying.
The diffuser is open to a car's base. It's directly linked in both directions. High pressure will always induce flow in the direction of low pressure. Just like with separation.
If underbody flow stalls on a steep diffuser ramp, and base pressure now dominates the immediate region, if that pressure exceeds what is upstream, the air would consequently move in that direction. As in the A-pillar analogy.
There's a reason why the Lamborghini demonstrated reverse-flow. Any explanation would have to include a look at local pressures.
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