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Old 12-23-2020, 08:18 AM   #23 (permalink)
AeroMcAeroFace
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Quote:
Originally Posted by JulianEdgar View Post
I'll be blunt - Aerohead's description of how diffusers works is so ridiculous that no reference is ever going to mention his theories.

As far as I can ascertain, Aerohead believes that lift/downforce comes from separated flow, so he assumes the diffuser is always in separated flow and it's wake pressures doing the work. But of course pressures from attached flow can be much greater than wake pressures, so no one would think that way. (Unless you'd read only a 1987 book where separation was common, of course.)
There is a difference here between low angles used in drag reduction and high angles used for downforce:

at low angles "under-body diffuser is all about generating a pressure recovery to increase the base pressure"

"An under-body diffuser requires attached flow to enable pressure recovery"

But that is in a PhD thesis, so in aeroheads mind is completely invalid.

But in high angles, there is separation, which would lower base pressure, I don't know about backwards flow, but there is definitely separation. But the angle at which separation occurs is influenced (as always) by what occurs upstream and vorticity. And separation angle can be anywhere between 6 degrees and 30 degrees.
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