Ferrari F12 AeroBridge

[Viturro]

''Viturro, the high pressure low pressure thing with velocity phrase is taken from the what makes airplanes fly rule book.'' That's the old concept of why airplanes fly.
''Wasn't the N.A.S.A. the ones that say that the air planes didn't fly because of Venturi effect, they fly because the wings send the air below it?'' with Venturi effect i mean the pressure things :P, and with ''they fly because the wings send the air below it'' i mean that depending on the volume/amount/weight and the distance that the air is deflected from his ''natural'' position there is a force that counteracts making the plane fly, no pressure things matter.

my dad's car (passat b5.5 2004) have that kind of naca duct on it's flat underbody

[kach22i]

Originally Posted by Viturro

........ they fly because the wings send the air below it?''.......

Getting off topic here.

I've read good discussions on that topic (in a Physics forum), and would rather not revisit them here.

If you want to learn more about velocity and pressure try Googling divergent and convergent thrust ducts as I did for my hovercraft research.

Back to the topic of air management, I think Ferrari's claims are overreaching but that there is something valid to it.

Just my opinion.

[Viturro]

Well you're right, off topic here, and thanks i will try Googling for some more info!

[Blue Angel]

Originally Posted by kach22i

Back to the topic of air management, I think Ferrari's claims are overreaching but that there is something valid to it.

Agreed.

The feature obviously does something, but exactly what that something is will likely remain a mystery.

I tend to think the stylists had as much or more to do with the initial concept of this idea as the aero guys did. If the stylists want to add something for visual reasons, as long as it is at least aero-performance neutral they would have no reason not to allow it.

Looking at it another way, the stylists could have been pushing the large bodyside scallop, and the aero guys may have resisted it because it disrupted airflow down the side of the vehicle. Coming up with a vent to "fill" that scallop may have been a way to please both parties while giving the marketing team something really "innovative" to run with... a win-win-win.

This feature may not reduce drag or improve downforce at all, but the marketing folk can tell you whatever they think you want to hear.

[freebeard]

It occurs to me that anyone who could afford this car could easily afford an hour of wind tunnel time and two scraps of coroplast to make plugs for the vents. Nobody else really needs to care.

Viturro -- All this thinking about high/low pressure/velocity makes my head hurt. With no more education than following threads here for a few months, I've come to look at it this way. The air and ground plane don't move, the car does. The air only tries to regain an even distribution of the ambient pressure, and it does it according to certain rules.

Aerodynamic features that work inside a pipe (Venturi effect) also work on the outside, it's equivalent to a pipe of arbitrarily large diameter. A vehicle could be considered an inside out musical instrument, with the goal to mute it as much as possible.

[offtopic]
If/when I don't have a working spedometer I can tell 45mph because the exhaust is the same note that Johnny Cash hums as the first note of I Walk The LIne.
[/offtopic]

You get fluttering areas of high and low pressure (always in turbulence at ground level) that are subsonic noise (not always subsonic—I'm looking at you, driver's door mirror), which provides a medium for vortexes. Kind of like regular weather can cause tornadoes.

Coaxing the air to part gently with minimal lateral acceleration, and then to refill the wake without [insert word for rotation around direction of travel] movement, which causes vortexes, is the goal.

[brucepick]

Originally Posted by freebeard

Sorry, what kach22i said. It's an external aero duct...

I think the Ferrari is a good example, diverting air sideways before it piles up under the windshield. I don't know if it would do much downstream...

In my humble opinion, the negative lift benefit is from more than just preventing air flow from piling up on the windshield. The design defeats the usual upward lift airfoil of the car body, by causing more air to flow around the sides instead of over the top.

Normally the car body serves as an airfoil, creating lift. By removing air flow and sending it out the sides a portion of the usual lift is removed. So it's a relative downforce.

By setting up an upside down airfoil along the side (flank), the benefit is increased., if indeed the air follows that pretty path.

I think the re-directing of the air flow creates drag, unless the angles and curves are kept very gentle. But the negative lift benefit probably is real.

[freebeard]

Agreed, except that it's more of a wing-tip than an airfoil. Which are notorious for not contributing lift.

And I didn't describe the upstream effect very well.

[aerohead]

Originally Posted by kach22i

If I'm thinking correctly you are asking about the section of the car/truck body which is typically flat across the rear.

In this case there is no flow of air.

No higher pressure or lower pressure, only a lack of pressure caused by the vehicle body moving though the air.

In part, the rolling vortexes of turbulence at the rear corners, end/top of vehicles are permitted to form because of this lack of pressure.

Had there been pressure back there, air flow could not go crazy and would be forced to conform to a flow, much as it does against the skin of the vehicle body. The body of the vehicle exerts an equal pressure, if it does not, it will flex like fabric does.

*The absence of 'body' at the vehicles rear triggers flow separation.
*As the air separates,counterflow initiates the formation of eddies,the boundary layer lifts away,and full-blown turbulence takes form.
*The base pressure of the turbulent wake is governed by the pressure at the separation point and this pressure is communicated throughout the entire wake region.
*This base pressure is what streamlining attempts to reduce or completely eliminate.Which in turn reduces or eliminates the pressure drag,the major constituent of profile drag.
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The kinetic energy of the turbulence cannot ever be converted to useful pressure.It is lost forever to heat,as viscous attrition,over hundreds of feet behind the car,will eventually wear down the turbulence,eventually re-calming the air as if nothing ever happened.
It's a perfect example of the 2nd Law of Thermodynamics' entropy.
*Once you've broken Humpty Dumpty,you can never put him back together again.