sunroof ... vent

[fearlessjoe]

thats proably a stupid title .....

this is my first real post on here... so hi

has anyone ever thought about .... i dont know how to describe it..... making air vents that run from a sunroof and or side window to out the back window or some kind of make shift 'vent hole'

so if you didnt have anyone in the back you could channel air to behind the car


allow my bad 2d ms paint job to ellaborate



the idea being the channel could be made of something like single ply sheet of plastic... carbon fiber if its fancy, so it could all unclick and be mounted flat to the inside off the roof for use of the back seats

that way the side peices can have a channel that the bendy top and bottom peices click into and the same for the side windows that could be rolled down for use as vents

you would have to have some kinda rear window replacement you could attach for use when there are people in the back or parked up

opinions

[Frank Lee]

The concept pops up with some regularity. Searches will probably reveal that.

Personally I think it's pointless to run ducts for aero; ducts have drag too and if the vehicle has so much extra room it can handle a duct, a better option would be to chop the top and reduce frontal area.

[aerohead]

[QUOTE=fearlessjoe;494724]thats proably a stupid title .....

this is my first real post on here... so hi

has anyone ever thought about .... i dont know how to describe it..... making air vents that run from a sunroof and or side window to out the back window or some kind of make shift 'vent hole'

so if you didnt have anyone in the back you could channel air to behind the car


allow my bad 2d ms paint job to ellaborate

The problem is that the air behind the car is at a higher pressure than at the windshield header/A-pillars.
If you open the vent,air will move forwards towards the low-pressure area,defeating it's purpose.
Also,any air robbed from the outside of the car's body (going through the vent duct),destroys the the boundary layer where it might have flowed,so you have even worse flow separation and higher drag than if you did nothing.

[RedDevil]

Hi, and welcome!

In aerodynamic work the main area to improve on to reduce drag is the middle to aft area. The front does not matter much - the air has to be pushed aside to let the car through anyway.
So you put your attention to the right area

Now most cars today have their roof line gently curved down towards the back.
The reason it is curved down is to reduce the wake by making the air reposess some of the area it was pushed away from.
The reason that curve is gentle is to ensure the air does actually follow the contour instead of breaking free in turbulence, which would defy the concept.

One problem is that any change in direction causes a low pressure area (or more correctly, you need a low pressure area to make the air flow change direction towards it).
Such areas are inherently unstable, if air can flow towards it from the sides it will.
Make a nice curved roof on a car with flat sides and air will roll from over the sides to the top with nice vortices etc.
So to prevent that it is best to taper the sides too.

One good example of an optimized taper can be found here: http://ecomodder.com/forum/showthrea...ion-21952.html

As I said, the roof often shows more curvature than the sides.
So your idea might work if applied to the sides, where it is needed more.

For instance, make the rear side windows taper slightly inside to funnel some air along the inside of the rear quarter pillars to slots inside the side edges of the back window.
Or by channeling air from the side to the rear wheel wells behind the wheels and out through holes in the rear bumper or something like that.

Anyway, I like the channel (funnel/duct!) idea and hope this thread will reveal if and where it is used on cars other than front bumper to front wheel well - we know all about that from MB and several sports car manufacturers.
Subscribed!

[fearlessjoe]

Originally Posted by Frank Lee

The concept pops up with some regularity. Searches will probably reveal that.

Personally I think it's pointless to run ducts for aero; ducts have drag too and if the vehicle has so much extra room it can handle a duct, a better option would be to chop the top and reduce frontal area.

i couldnt find anything when i looked.... i was probably looking for the wrong thing though

chopping the top is fine but if you drive a large car like an estate its probably because you sometimes need to room........ i spose a fold down roof... sometimes a full size car... folds down to a teardrop would work better.... thats seems less achievable though

[RedDevil]

As Aerohead mentioned vent holes often behave contradictory to what you'd expect.

One stunning example is the bonnet scoop on the 2000 Subaru Impreza Turbo. That scoop allows air to flow through the intercooler.
One Impreza owner set out to measure the air flow and found that the scoop actually released air instead of taking it in.

The reason for that is simple; the high pressure area ahead of the big grill makes sure a lot of air flows into the engine bay, and it has to go somewhere.
The bonnet is slightly curved and creates negative pressure overhead.

One of my friends did own a couple of Subarus and noticed that at 250 kph on the Autobahn the bonnet was ballooning upwards, so much so that he thought he damaged it permanently. When he dropped the speed the bonnet sank back into position; apparently it could cope with the flexing.

But who would have expected the air flows out of that front facing bonnet scoop instead it into it?

[fearlessjoe]

i see what your saying.... and i dont pretend to be a big expert.... or a little one lol...

i may be wrong but in my mind the back of the car where the air is all being dragged along by the car has to be a low presure area surely... compared to the roof anyway... thats how it looks to me from the first pic i found below

so it seems like it would get sucked through... you would obviously need to actually know what you were doing to make it work, size of entry and exit... shape of it

roof inlet or scoop.... i dont know im just thinking outloud

[spacemanspif]

For My Ally Is The Force, And A Powerful Ally It Is - Speedhunters

This article pops up whoever people talk about killing the vacuum at the rear of the car.

[aerohead]

[QUOTE=fearlessjoe;494733]i see what your saying.... and i dont pretend to be a big expert.... or a little one lol...

i may be wrong but in my mind the back of the car where the air is all being dragged along by the car has to be a low presure area surely... compared to the roof anyway... thats how it looks to me from the first pic i found below

so it seems like it would get sucked through... you would obviously need to actually know what you were doing to make it work, size of entry and exit... shape of it

roof inlet or scoop.... i dont know im just thinking outloud[/QUOTE
*The lowest pressure on the car is near where your inlet is,(the massive yellow area above the roof)

*The pressure where your outlet would be is at a higher pressure.
*The flow would be backwards.
*The boundary layer would be destroyed and you'd have higher overall drag.
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*You can't trick the air.
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*Your drag is caused primarily by the pressure differential between the front stagnation point and the base pressure of the wake.
*The only way you can reduce the drag is to elongate the body with a streamlined profile to either reduce,or eliminate the wake.
*This profile is what the air wants to see.It's the granddaddy of low drag cars

*You just extend the body as far as you're willing,then chop it off like you'd do a loaf of bread


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*If you had a free energy device,you could blow air into the wake and this would definitely reduce drag,but it won't work as a passive device.About 60-researchers have tried so far,all unsuccessful.
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