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Old 09-02-2020, 02:11 PM   #8 (permalink)
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Originally Posted by JulianEdgar View Post
I am afraid this is just gibberish.

What does 'hypo-contour' mean?

What is 'off the reservation flow'?

What does 'sequestered' mean?

And what is 'contour corrupted'? (title of thread)

To be honest, Aerohead has developed his own weird theory and then has to develop his own vocabulary to describe it. None of this stuff is in any current textbook on car aerodynamics.
1) hypo is below contour.
2) off the reservation is off the profile
3) sequestered is, the flow instability (separation bubble ) is captured between the backlight and end of boot,with no chance of making it to the 'base' of the car and contaminating it with low pressure.
4) 'Corrupted' means that the ground rules of fluid mechanics are violated by the shape. The 'template' contour produces laminar flow. By straying off the template contour you jeopardize the boundary layer which is responsible for flow separation, which is responsible for pressure drag.
5) all streamlining has to do with minimizing, or eliminating flow separation.
6) The Cadillac poses only a small perturbation. It's virtual lack of rear lift is a testament to the pressure-producing capability of a streamlined shape.
If you'll revisit Figure 2.4, page 51 of Hucho, you can see how,over the last 14.5% of the body, local pressure rises all the way back to local barometric pressure. Depending on rear overhang, and low pressure under the body, due to a diffuser, rear lift can be zero, like the VSPORT's.
7) In Hoerner's Fig. 9.4 page 160, you can see the Jaray car Sawatzki tested in 1941, with atmospheric pressure acting on the nose, a large pulse of positive pressure acting against the cowl area, then the last 23% of the body under a positive pressure gradient, acting at a distance behind the rear axle, like a wing on an F1/Indycar, or your cantilever spoiler on the Insight.
Sure would be cool if you could get into Bernoulli's Equation and Mair's and Buchheim's work on boat-tailing. Only then will you understand the value of 'corrupting', or what Lanchester referred to as 'mutilating' the streamline body.
Nobody disputes your pressure measurements, but there's an issue with the quality of the body shape you're measuring, as related to boundary layer 'health' that must be addressed. This is where I'm coming from. And it's something your aeronautical engineer and aerodynamicists may have never had to contend with, as 'low drag' may never have been a priority with the legacy carmakers they worked for. Don't know.
The new head of design for Volvo's Polestar Division is having to overcome a lot of institutional inertia with parent Volvo, who's always relied on selling 'emotion', not technology.
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