Quote:
Originally Posted by California98Civic
If the vortices are the problem and the fastback shape is otherwise known to have more potential for reducing drag and lift when undertrays, diffusers, spoilers, and fins are used, then why not explore reducing the vortices off the pillars by tapering and radiusing the fastback's full rear body contours more?
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I am not sure that is the best approach. In many cases, it appears more to be the shape of the C-pillars. I don't know of any comparative testing that has been published, but just by observation it's my guess (and only a guess) that C pillar designs that prevent airflow wrapping around the pillar onto the rear window reduce the strength of the vortices on fastback shapes. In other words, the more the airflow can be kept travelling longitudinally, the better.
If you look at the XL1, you can see this may well occur:
My tuft testing of the Tesla Model S shows this occurring:
..and the rear view shows the shape of the pillars well.
The Taycan is very similar:
Contrast that with my tufting of the XE Jaguar, for example, where you can clearly see airflow wrapping around the smoothly curved pillars:
...and look at how low the pressures are on the upper part of the rear pillars
(hotter colour = lower pressure).
(And if you look at the tuft and CFD images of the Jaguar, you can see - of course - that lift is created by the attached airflow... and not some weird theory that separation is responsible for lift on these shapes.)