Fender vents and Separation Traps

[Phase]

https://bimmertips.com/fender-vents-...s-the-purpose/

any thoughts on fender vents for the wheel wells? bmw uses them on the front

and mercedes is even using them in the rear for their super low drag EQS



also hyundai uses something called '' ''separation traps on both sides of the rear bumper '' for their new ioniq 6 which is also low drag, but they never specifiy exactly what they are or how they work.


https://www.wardsauto.com/vehicles/a...ys-ioniq-6-bev


anyone have any guesses on the rear separation traps?

[freebeard]

It's hard to offer an opinion when they never specifiy exactly what they are or how they work.



Harry Bentley Bradley in 1981.

[Phase]

Originally Posted by freebeard

It's hard to offer an opinion when they never specifiy exactly what they are or how they work.



Harry Bentley Bradley in 1981.

pressure increased in the wheel well creates drag and lift both and noise. the vents all the air to exit out of the high pressure wheel wells

[freebeard]

pressure increased in the wheel well creates drag and lift both and noise. the vents all the air to exit out of the high pressure wheel wells

Your just restating the most obvious thing. My example was from 1981.

It doesn't answer what is a 'separation trap' anyway. How does it differ from a Faschenfeld tearing edge [as seen on the new Prius]. It's in the bumper, is that them below the reflectors?

Here's a properly designed front fender.


This one has a tight raidius, but massive venting on the top.

[Phase]

Originally Posted by freebeard

Your just restating the most obvious thing. My example was from 1981.

It doesn't answer what is a 'separation trap' anyway. How does it differ from a Faschenfeld tearing edge [as seen on the new Prius]. It's in the bumper, is that them below the reflectors?

Here's a properly designed front fender.


This one has a tight raidius, but massive venting on the top.

I have no idea why Hyundai mentions separation trap or tries to act like it’s unique

And you mean the Prius prime versus normal Prius? Where the led lights are?

Isn’t it essentially just a super hard separation edge with like an inch mini box cavity essentially?

[freebeard]

....a super hard separation edge with like an inch mini box cavity....

As good a theory as any.

[aerohead]

You're looking at $100,000 in R&D to tune one of them. It's not for shade-tree aerodynamicists.
There are dozens of lower drag cars which never had them.

[Phase]

Originally Posted by aerohead

You're looking at $100,000 in R&D to tune one of them. It's not for shade-tree aerodynamicists.
There are dozens of lower drag cars which never had them.

If I cut a hole in the back side of the rear fender, how would it hurt drag though? May not improve it but I don’t see how it would hurt. Still a thought

The rest separation trap seems interesting though like what the Prius prime has too. Pretty much just a small partial box cavity. Which should be easy to fabricate

[aerohead]

Originally Posted by Phase

If I cut a hole in the back side of the rear fender, how would it hurt drag though? May not improve it but I don’t see how it would hurt. Still a thought

The rest separation trap seems interesting though like what the Prius prime has too. Pretty much just a small partial box cavity. Which should be easy to fabricate

If you've looked at some of the pressure coefficient distributions shared here at EcoModder.com, you'll notice that the 'deadwater' base pressure behind cars can be HIGHER than forwards on the body, where air is moving faster.
Look at VMAN 455's website and Edgar's, or Edgar's book.
If you were to arbitrarily open a pathway like that, you could easily see air flowing forwards through the breach, exactly what you're trying to avoid.
It doesn't hurt BMW and Lexus and Mercedes to drop a few million dollars on CFD or wind tunnel time to 'dial-in' such small details.
In this instance, you'd want to drop your money on the pizo ports, Tygon tubing, and Magnehelic so you could 'know' in advance if the IONIQ could produce rearwards-directed flow from the wheelhouse. It's not a given.
Besides those openings need to be fully-skirted, something Mercedes wasn't willing to do, but would have had lower drag if they had.

[freebeard]

you'll notice that the 'deadwater' base pressure behind cars can be HIGHER than forwards on the body, where air is moving faster.

So the question becomes: Are the speed holes on the rear face or behind the wheel well?

Time attack race cars vs a cutaway fender.