Making the Ioniq slippier

[Phase]

Originally Posted by airbiteses

hmm, you could put something flat in this place ...

i think hyundai put that there for some type of acoustic effect i remember. plus the boundary layer is usually thicker near the rear of the car anyways

[freebeard]

Any type of acoustic effect would be lost in the noise.

[Phase]

Will be starting to cut out final ABS section in a few hours and attaching. May also add on a little extended diffuser with the left over plastic

[COcyclist]

Would you consider posting your 90 day mpg in your signature?

[Phase]

Originally Posted by COcyclist

Would you consider posting your 90 day mpg in your signature?

I don’t track it. I reset my mpg during each trip I do. I’ve posted my steady state speeds though at increments of 5 mph

[aerohead]

Originally Posted by Phase

Final design of my box cavity fins that are tapered inwards. Will be cutting out abs plastic and mounting the final ones full time! Any thoughts before they go on the car forever?

Currently, from Jeff Howell et al., at Loughborough University in England, your drag reduction will be the area of the new wake, compared to that of the OEM wake, as a percentage, multiplied by the OEM Cd. And that presumes fully-attached flow rearwards along the tapering panels.
From the photographs it's impossible to 'measure' the before and after dimensions, so no prediction is possible.

[Phase]

Originally Posted by aerohead

Currently, from Jeff Howell et al., at Loughborough University in England, your drag reduction will be the area of the new wake, compared to that of the OEM wake, as a percentage, multiplied by the OEM Cd. And that presumes fully-attached flow rearwards along the tapering panels.
From the photographs it's impossible to 'measure' the before and after dimensions, so no prediction is possible.

From studies I’ve read, the wake size will be smaller than just the measured “ edges” of the cavity fins if I taper them in because then that wake extends inwards with a different vortex layer. It forms an “ invisible boat tail” that the outside air flow skims across. Not to mentioned the rear base pressure increases too from the cavity affect. I’ll be tuft testing them and then heat molding the taper inwards while maintaining attached airflow.

Was thinking of doing the same thing under the car with a diffuser, pretty much just acting as a horizontal box cavity fin. It should also help with snow and rain build up on the back of the car and keep the backup camera cleaner too I believe

[Phase]

Cut out and sanded down. Attaching them after the rain

[Phase]

The fins are officially on! Drilled in at 3 points with double sided 3m vhb mounting tape along the edges between drill points. Letting it sit over night so mounting tape adheres better before driving. I need a heat gun to curve the plastic inwards to add a taper. The plastic is much harder to shape than poster board or cardboard clearly

[aerohead]

Originally Posted by Phase

From studies I’ve read, the wake size will be smaller than just the measured “ edges” of the cavity fins if I taper them in because then that wake extends inwards with a different vortex layer. It forms an “ invisible boat tail” that the outside air flow skims across. Not to mentioned the rear base pressure increases too from the cavity affect. I’ll be tuft testing them and then heat molding the taper inwards while maintaining attached airflow.

Was thinking of doing the same thing under the car with a diffuser, pretty much just acting as a horizontal box cavity fin. It should also help with snow and rain build up on the back of the car and keep the backup camera cleaner too I believe

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.
--------------------------------------------------------------------------------------
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.
--------------------------------------------------------------------------------------
Also, you have a 'cavity', but a 'box-cavity' is an entirely different animal.
--------------------------------------------------------------------------------------
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.