Making the Ioniq slippier

[Phase]

Originally Posted by aerohead

Yeah, if you can find the sweet-spot, where the inward curve is just right, you'll pick up a smidgeon of pressure recovery.
You'll have the 'smaller' wake, AND it will be of higher base pressure.
Is there a reason for 'saw-toothing' the fins?
The pressure at the trailing edge of the 'point' is going to be greater than at the shorter inclined locations, a setup for shear-induced vorticity, something you want to avoid like the plague.
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The SAAB 9.3 was tested with and without a rear diffuser, and it had no effect at all on drag, as the car had no complete belly pan ahead of it. If you haven't already paneled in the underbody, you might run into the same situation. Don't know. It's a $4,000 answer.
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Also, you have a 'cavity', but a 'box-cavity' is an entirely different animal.
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The tearing edges will help reduce vorticity, and the wake will kind of 'look' like an imaginary boat-tail, but it has no facility for pressure recovery, as with an actual boat-tail, tapered cavity, or box-cavity.
And measuring from the IONIQ blueprint, there's no chance of any 'phantom' tail affect until you've got 140-inches of boat-tail behind the car.

The pointy shape is just an extension of the originally OEM hard separation edges that Hyundai already tested in the wind tunnel. I didn’t want to alter the rear side shapes because I have no idea how it would affect up wash or down wash or wake shape. I cut the inside shape to add a more stylized sporty look. In all, it’s just an extension of the original sides from Hyundai. The poster board tests with the same shape and duct tape already gave me a 4 extra mpg boost from testing before.

[aerohead]

Originally Posted by Phase

The pointy shape is just an extension of the originally OEM hard separation edges that Hyundai already tested in the wind tunnel. I didn’t want to alter the rear side shapes because I have no idea how it would affect up wash or down wash or wake shape. I cut the inside shape to add a more stylized sporty look. In all, it’s just an extension of the original sides from Hyundai. The poster board tests with the same shape and duct tape already gave me a 4 extra mpg boost from testing before.

I'm just saying that, if you have a constant-contour in these 'fins', that, at the trailing edge, there will be a mandatory difference in velocity and pressure, which will introduce vorticity, something which would not occur if you simply made the trailing edge 'vertical', like Koenig-Kamm did in the 1930s.
Hyundai/ KIA / Genesis is going to do exactly this next year on one of their big SUVs.
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' ... angled inward...the airflow remains attached until the trailing edges...the resulting wake will be smaller.' Julian Edgar, 2018, p.131
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' A wide wake does not necessarily imply a low rear end pressure; in fact, the reverse can be true.' Julian Edgar, 2018, p.11
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( Another contribution to drag arises from trailing vortices...) Julian Edgar, 2018, p.11
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' Trailing vortices are shed by angled, upright edges...' Julian Edgar, 2018, p.17
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' The flow separations that lead to a pressure drag can be... inclined separation line flow separation shed vortices with axes roughly parallel to the separation lines with well-ordered, steady three-dimensional flow separation on the rearward surface, inducing a suction which leads to a pressure drag.'
Hucho, 1986, p.59-60, 2nd Edition

[Phase]

I need a heat gun to curve the edges inwards a little more. Right now they are just an extension of the rear edges creating a hard separation edge and cavity. Luckily the rear of the Ionia is slightly tapered anyways at the end before the oem separation edges

[freebeard]

Practice on some scraps first?

[Phase]

https://youtu.be/KICvXyv0IOc?si=CAzT9YdGG-S5BOGn

Here’s a walk around if anyone is curious. They look better in person too

[freebeard]

Needs skegs.

[Phase]

Originally Posted by freebeard

Needs skegs.

The wheel covers are coming off in 2 months anyways for snowboard season

[aerohead]

Originally Posted by Phase

https://youtu.be/KICvXyv0IOc?si=CAzT9YdGG-S5BOGn

Here’s a walk around if anyone is curious. They look better in person too

To optimize the performance of the 'cavity', those top and bottom gaps could be sealed any way that you can.
Otherwise, the pressure recovery is adulterated by the leakage.
Your looking for what Hyundai is doing with next year's IONIQ 7

https://www.caranddriver.com/hyundai/ioniq-7

[Phase]

Originally Posted by aerohead

To optimize the performance of the 'cavity', those top and bottom gaps could be sealed any way that you can.
Otherwise, the pressure recovery is adulterated by the leakage.
Your looking for what Hyundai is doing with next year's IONIQ 7

https://www.caranddriver.com/hyundai/ioniq-7

It’s hard to see but the tail lights have a little cavity separation edge built in. It’s hard to see. It’s not perfect though

[Phase]

This still safe for a muffler? Idk what it means