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Old 06-03-2021, 06:53 AM   #121 (permalink)
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Looks like it is working really well with good attached flow on the topside bits but not great attachment on the part by the brake light, but then it reattaches before the end so I would guess at that being a positive.

There is an audi a2 study using a box cavity and they found that the best diffuser varied based on the box cavity. https://www.a2oc.net/community/index...642#post165642

I don't see people doing things like this nearly enough anymore
Completely agree.

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Old 06-03-2021, 10:21 AM   #122 (permalink)
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box cavity

https://ecomodder.com/forum/member-a...ing-effect.jpgHere's a $425,000 box cavity. https://ecomodder.com/forum/member-a...ion-plates.jpg
All the trailing edges are positioned where the trailing edges of an ideal boat-tail would be.
Between the separation line and the trailing edges, vortices are captured within the confines of the intentional void.
Outer flow follows over the outer 'surface' of the vortex, creating a virtual boat-tailed 'surface' of this 'dead' pool of air, on top and sides. ( the bottom is ruined because of the rear wheel turbulence and DOT bumper.
In order for the vortices to be captured, the rear edges of the cavity must be located at the 'streamlined' position.
* Your top is fine, it's a flush continuation and extension of the profile.
* The bottom seem okay as well.
* The sides however, seem too far inset to allow for vortex capture, producing unstructured turbulence instead.
I've added W.A. Mair's boat tail. It's outer contour would illustrate where 'edges' should be positioned.
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Old 06-03-2021, 10:53 AM   #123 (permalink)
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If you do a rear diffuser, you should re-test. A really good comprehensive study of box cavities I saw, found that the cavity intereacted a lot with the diffuser. You'll want to tune the combination.

See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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