[aerohead]

Originally Posted by JulianEdgar

If you strip away the obscure language, it's actually easy to understand.

Old shape cars (eg notchbacks) had flow that separated at the end of the roof. So, my old W123 Mercedes shows flow separation from the end of the roof:



Note the tufts on the rear window and boot / trunk lid show separation (they're whirling around, not lined up in flat rows.) Basically, the wake extends to the height of the roof.

Conversely, modern cars have attached flow across the boot / trunk:



Note the tufts on the rear window and boot / trunk lid show attached flow (they're not whirling around but instead are lined up in flat rows.)

As far as I can ascertain, Aerohead believes the flow pattern shown on the Jaguar isn't real, in part apparently because the rear contours of the Jaguar dip more sharply than his Template. He believes that the flow is really separating far forward. (In fact, he has said at least once that it is separating at the windscreen header rail, believe it or not.)

Now to lift. If we look at the old Mercedes, we can see the boot / trunk lid is in separated flow, so in effect it is within the wake. The wake is a low pressure area and this low pressure is bearing on the boot / trunk lid, so causing lift. So in the old cars that Aerohead likes citing, in fact separated flow was causing lift.

But this theory is obviously quite invalid for modern car shapes (there's almost no separation), so where is the lift coming from? It is coming from the airflow wrapping around (ie attached to) the upper curves, so generating low pressures.

Here those low pressures can be seen on Jaguar CFD (hotter colour = lower pressures):



Not the low pressures all across that curved roof and part way down the rear window. The blue areas show that in fact Jaguar claim positive pressures on the boot lid (achieved by the rear spoiler).

My Insight shows it well - note the measured lift across the upper curves. The Insight has attached flow on all upper surfaces. (Length of arrows shows magnitude of force.)




So:

• the shape of the car determines the airflow pattern
• car shapes have changed a lot in the past 60 years
• theories of airflow need to take into account what is happening on current shape cars

Unfortunately, Aerohead has built entire theories on faulty and / or outdated premises, and then extrapolated them to the point where a great deal that he writes is completely wrong. (Not everything, but a lot.)

He then denigrates the real experts. Who? Well, he has made adverse comments here on a number of aerodynamicists, including the head of Porsche aero, the head of Jaguar aero, an F1 aerodynamicist, a former Tesla aerodynamcist - and so on.

So he doesn't read current aero literature, and doesn't want to learn from real experts.

That's not a good combination for giving people advice!

If you'd actually read Hucho's book you'd be stuck with the same conclusions.
Aeronautical engineer Larry Mauro doesn't know anything about automotive aerodynamics, although his friend Peter Brock certainly does.
My college chum Glenn got his Master's degree in aeronautical engineering from NASA, but it doesn't qualify him for automotive aerodynamics.
None of the car companies your associates worked for have generated novel low drag cars. The only reason Tesla gets a pass is because it doesn't have the cooling system and belly mutilations of a conventional ICE vehicle, otherwise, they're no better than a 1989 Opel Calibra.
Other than the popular literature, or what can be gleaned from online, my income precludes me from staying abreast of contemporary professional developments, however, the fundamentals don't change.
In 1986 Hucho thought the future would produce a Cd 0.20 car. In 1987, the Cd 0.19 Impact debuted. Hell of a ride! The future moved fast! I recommend we catch up to the past.