Vortex generators at rears?

[Phase]

So I’ve noticed a trend on a lot of modern cars using vortex generators at the rear of cars? Why is that? From my understanding, it detaches air flow and creates vortices that can reattach to other parts of the car, like a large wing on the back, or near side mirrors. So why the very rear?

The newest Hyundai Sonata uses them at the tips of its mini box cavity rear spoiler thing, the newest Elantra has a few on the sides towards the back past the rear windows, and many other cars have them on the side of the rear tail lights.

Can someone explain this?

[freebeard]

Making little ones out of big ones?

[Phase]

Originally Posted by freebeard

Making little ones out of big ones?

What do you mean?

[freebeard]

It was an obscure refrence to breaking rocks in prison. No wonder you're preplexed.

Generically the wake is two counterrotating vortexes, up on the sides and downward in the middle. Those would be the big ones.

The vortex generators add energy, harvested from drag, to a zone that [otherwise] wants a sharp separation edge, Similar to a wickerbill the flow is reoriented toward the centerline, reducing the volume. Those would be the little ones

[Phase]

So maybe put a VG here in the smooth pocket since they didn’t put a hard separation edge? Would that do the same effect?

[freebeard]

That would be a question for Doctors Tuft and Testing.

[aerohead]

The aeronautical engineer who 'invented' what we know today as 'Air Tabs', created them to solve the 'problem' of detached flow over the boot/trunklid of his Honda Accord notchback.
The VGs created the tiny, high-suction, delta-wing vortices employed by the likes of the Concorde SST and Space Shuttle, to help induce the turbulent boundary layer to remain attached down the backlight, enough to reattach onto the rear of the car, before leaving the car, capturing a separation bubble, isolated from the rear panel.
The small amount of air crashing against the top of the boot, provided a higher static pressure just ahead of the 'new' separation line, and when the flow separated at it's new location, it exposed the 'base' of the Honda to a higher pressure than would exist, had the flow been totally trashed.
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The key to a VG's performance is that, it have some 'surface' downstream, on which the flow may attach.
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The IONIQ has no such structure.
Also, the area you've marked already has a burst edge, from below the taillight lens, down the slanted side of the rear fascia.
You don't want flow attached in there, as it's prone to bistable flow ( hunting separation line/ acoustic 'booming' ).
My opinion would be to ignore VGs. There a solution to a problem that you don't have.
Your call.

[Phase]

Originally Posted by aerohead

The aeronautical engineer who 'invented' what we know today as 'Air Tabs', created them to solve the 'problem' of detached flow over the boot/trunklid of his Honda Accord notchback.
The VGs created the tiny, high-suction, delta-wing vortices employed by the likes of the Concorde SST and Space Shuttle, to help induce the turbulent boundary layer to remain attached down the backlight, enough to reattach onto the rear of the car, before leaving the car, capturing a separation bubble, isolated from the rear panel.
The small amount of air crashing against the top of the boot, provided a higher static pressure just ahead of the 'new' separation line, and when the flow separated at it's new location, it exposed the 'base' of the Honda to a higher pressure than would exist, had the flow been totally trashed.
--------------------------------------------------------------------------------------
The key to a VG's performance is that, it have some 'surface' downstream, on which the flow may attach.
------------------------------------------------------------------------------------
The IONIQ has no such structure.
Also, the area you've marked already has a burst edge, from below the taillight lens, down the slanted side of the rear fascia.
You don't want flow attached in there, as it's prone to bistable flow ( hunting separation line/ acoustic 'booming' ).
My opinion would be to ignore VGs. There a solution to a problem that you don't have.
Your call.

yeah the separation edges are lower though. the little 2 inch rounded section doesnt have separation. so i should just put a hard separation edge there too as part of my future mini box cavity?

[aerohead]

Yep, that would handle it.

[Phase]

Originally Posted by aerohead

Yep, that would handle it.

would look better too


thoughts on this newer paper? digging the fins lol

https://aia.springeropen.com/article...74-020-00054-7



also heres an interesting study on sep edges- https://core.ac.uk/download/pdf/33664561.pdf