Quote:
Originally Posted by aerohead
1) No. 3 smoke filament from the floor makes it into the boundary layer over the roof.
2) The roof contour does not follow the local streamline.
3) The roof has produced too much of a pressure rise.
4) The pressure rise has decelerated to flow.
5) The decelerated flow has lost momentum.
6) Now there's not enough momentum transfer to the lowest stratum of the TBL adjacent to the body's surface boundary.
7) Without a reduction of the pressure the TBL must separate and does.
8) The separation is inducing a weak pair of attached longitudinal vortices.
9) The vortices are inducing a weak downwash.
10) The downwash is holding the flow attached down the centerline..
11) The wake is 'smaller' but overall total drag is higher than if the roof was 'streamlined', on account of the induced vortex-drag.
12) Vortex drag is the highest form of drag.
13) Later addition of the spoiler will allow the flow to reattach onto the spoiler's raised height.
14) The modified flow will force a higher velocity.
15) The higher velocity will produce Dr. Thomas Wolf''s ' stronger negative pressure gradient.'
16) The stronger negative pressure gradient will re-invigorate the TBL.
17) The TBL will now flow over the separation bubble created by the spoiler.
18) When the flow does separate at the spoiler, it will be at a higher static pressure.
19) Lift will be reduced.
20) Drag will be reduced.
21) Again, attached flow due to downwash is not 'attached flow.'
22) Downwash is an artifact of separation, as is the vortices.
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The normal mix of correct theory, incorrect theory, irrelevancies, very clearly no experience of on-road testing of a shape anything like this, extrapolated even weirder theory - and so on.
For people who actually want to learn, just look at the pressure chart and the flow pattern, and draw some obvious conclusions about the relationships.
And as for the rear spoiler, just mentally place one at the back of the car (say, the same angle as the windscreen but only 1/5th as high) and then look at what the windscreen did to the pressure of the attached flow in front of it.