Mod for interior airflow?

[jamesqf]

Question for the aerodynamics experts: I've been reading arguments about windows down vs A/C, and just had a thought. You have a high pressure area somewhere at the front of the car, and a low pressure area at the rear. Suppose you take some - potentially a lot more than current vents supply - air from the front, and direct it through the car. You get the same cooling effect as rolling down the windows (if not a good deal more), some "wind in your face" effect a la convertible, no frigid breeze as with A/C... and it seems you'd actually reduce overall drag.

Make sense? Or am I missing something?

[SVOboy]

There have been a few attempts at this, two which I remember well.

In one tom attempted rolling down the windows and cracking the hatch, but ultimately found that while stopped having the hatch crack allowed fumes from the exhaust to sneak in.

In the second, back when dan kroushl drove a del sol, he could crack the windows and roll down the rear window to get a similar affect.

[SVOboy]

There have been a few attempts at this, two which I remember well.

In one tom attempted rolling down the windows and cracking the hatch, but ultimately found that while stopped having the hatch crack allowed fumes from the exhaust to sneak in.

In the second, back when dan kroushl drove a del sol, he could crack the windows and roll down the rear window to get a similar affect.

[jamesqf]

I think you would want to get a little more ambitious, and use ductwork (maybe flexible insulated furnace duct, to avoid picking up engine compartment heat) to lead from the intake to interior, then more duct from the rear of the passenger compartment to the outlet, with a backflow preventer so you don't get exhaust eddies.

My Insight does have something like the exit half of this, with vents on the rear (under the plastic rear shell) that close with flapper valves.

[Frank Lee]

The ventilation system is already set up that way.

[SVOboy]

One thing I have though about doing it cutting out the bottom of the back bumper and redirecting air up into the wake.

[MechEngVT]

Both my 2002 Ram and my 1988 Ramcharger work this way. The ventilation system draws air from the high pressure area at the base of the windshield. In my Ramcharger I have a really cool vent that opens by hand and lets this high-pressure air blow up your left leg. Completely without a blower, just pushed by air pressure.

In my 2002 Ram the back of the cab has vents that allow air to escape between the cab and bed which is a low-pressure zone due to the flow separation at the rear of the roof above this gap. In my Ramcharger, the whole truck leaks so much air out the rear hatch and through the doors that the air blown in from the front is free to escape to the lower-pressure air to the sides and behind.

I really don't think this is much of a new idea. Cars without significant aerodynamic aids generate lift and therefore the air inside the cabin is at a lower pressure than the air from the front. Going back into the 30-60s vehicles with the cowl-vent open to adjustable sliding or turn-knob floor vents allowed outside air to flow in due to dynamic pressure differential. The addition of vent windows magnifies this and adds some flow to the upper body when opening the vents widely, but that really hurts your aerodynamics. The prevalence of climate-control systems in modern vehicles has replaced the need for such low-tech devices in the marketplace, making them absent even on the few vehicles that can be obtained without climate-control (are there still any?)

[wagonman76]

What Ive done for years is open the front and back (door) window the same amount. It keeps me from getting blasted, and therefore I would think it would also reduce turbulence.

[aerohead]

Originally Posted by jamesqf

Question for the aerodynamics experts: I've been reading arguments about windows down vs A/C, and just had a thought. You have a high pressure area somewhere at the front of the car, and a low pressure area at the rear. Suppose you take some - potentially a lot more than current vents supply - air from the front, and direct it through the car. You get the same cooling effect as rolling down the windows (if not a good deal more), some "wind in your face" effect a la convertible, no frigid breeze as with A/C... and it seems you'd actually reduce overall drag.

Make sense? Or am I missing something?

Germans beat you to this 70-years ago! You need to track down a copy of Baron Reinhard von Fachsenfeld's "Aerodynamiks des Kraftfahrtzeugs" ( sp? ).It's all in there.I listed the particulars for the book in my seminars and installments.Inter-library loan is a good bet.I had to drive 30 miles to a university and copy it there.Good luck!

[trikkonceptz]

In a different topic on bellypans, someone said that aluminum screening would work well as a bellypan because the air would flow over it while allowing heat to escape.

Well along those lines I was thinking of making window screen that would use the glass and window channel along with a lighweight frame to hold it all together. Hence giving me the open window I desire while pushing air over it and not in my car. Don't know if it would work, but hell, once I am done with the pan, I'll use any extra material to try it out.

[jamesqf]

Originally Posted by Frank Lee

The ventilation system is already set up that way.

But the standard ventilation system doesn't provide much airflow, at least in any car I'm familiar with. Indeed, some of them don't provide ANY flow unless boosted by an always-on fan.

[Frank Lee]

I think that is a function of the flapper doors and ducting and stuff moreso than the intake and exhaust locations. I have old cars with cowl vents and they'll let in a gale force wind! Too bad they, along with wing windows, were discontinued.

[Xringer]

Back when I was a kid in the 50s, I lived in SW Texas. 100s in the summer south..
There were hardly any cars with AC. But, they all had flip up vents that directed air inside the car.

In most cases, there was a handle down under the radio (they used tubes back then)
and with you pulled it out, the vent input would flip up in the center, just behind the hood.
A lot of cars also had side vents. Same handle setup down low with the vents just forward of the front doors.


See that one just aft of the front right wheel?

[wagonman76]

Originally Posted by trikkonceptz

In a different topic on bellypans, someone said that aluminum screening would work well as a bellypan because the air would flow over it while allowing heat to escape.

Well along those lines I was thinking of making window screen that would use the glass and window channel along with a lighweight frame to hold it all together. Hence giving me the open window I desire while pushing air over it and not in my car. Don't know if it would work, but hell, once I am done with the pan, I'll use any extra material to try it out.

Its worth a try. The experts on the satellite dish forums (I still use a 10 ft c-band dish) say that anything over 25 mph wind or so, a mesh dish ends up acting like a solid dish anyway so it still gets the same effects from the wind.

[Xringer]

Originally Posted by trikkonceptz

Well along those lines I was thinking of making window screen that would use the glass and window channel along with a lighweight frame to hold it all together. Hence giving me the open window I desire while pushing air over it and not in my car. .

You got me thinking about those Solar powered Car Ventilator gizmos that
you stick on top of the glass and roll up the window on them..
Solar Car Ventilator

But, the amount of fresh air they bring in can't be close to enough on a hot day.

So, what about stealing that install location (on top of the windows) to place
a fresh air input on one side of the car and of the other side, place a warm air output.
The input would have a small scoop to bring in air
(making the cabin pressurized while at highway speeds)
and the output side would have the scoop point aft, to suck the air out of the car..

If you lived down in Texas, you might want to make the scoop large and maybe out of clear Plexiglas.

Something like this could go in behind the driver and not cause a blind-spot and use the mesh screen on the other side for the output?

Since it's taking in air, the drag won't be so bad.?.

[garys_1k]

Originally Posted by jamesqf

Question for the aerodynamics experts: I've been reading arguments about windows down vs A/C, and just had a thought. You have a high pressure area somewhere at the front of the car, and a low pressure area at the rear. Suppose you take some - potentially a lot more than current vents supply - air from the front, and direct it through the car. You get the same cooling effect as rolling down the windows (if not a good deal more), some "wind in your face" effect a la convertible, no frigid breeze as with A/C... and it seems you'd actually reduce overall drag.

Make sense? Or am I missing something?

It could certainly provide plenty of air, but to get enough to measurably reduce drag you'd have to have a LOT of air moving through the passenger compartment, way more than would be comfortable. Plus, you'd have to have very large inlet and outlet ducts, like half the area of the instrument panel and back seats.

[gascort]

Originally Posted by Frank Lee

The ventilation system is already set up that way.

Agreed; it's kind of fun to search for the exit vents on your car. I found mine; they are under the back speakers and they exit in the rear wheel wells.
To increase flow, I can crack my sunroof part way. My roof has a hump right after the sunroof anyway, so I assume most of the air pushed up re-attaches.
Matt

[markweatherill]

On a hot day, DIY brackets that allow a hatchback to be securely cracked/propped open a little would possibly help..? Maybe it would aid in finding the ideal rear roofline angle as an aside.

[jamesqf]

Originally Posted by garys_1k

It could certainly provide plenty of air, but to get enough to measurably reduce drag you'd have to have a LOT of air moving through the passenger compartment, way more than would be comfortable.

But understand that the primary objective is to get a comfortable (to me, tastes may differ) level of airflow through the cabin WITHOUT the negative aerodynamic effects of rolling down the side windows. If it in fact improves aerodynamics, that's a bonus.

As for the window scoop, there's this: KOOL SCOOP VENTS from Aircraft Spruce

Works pretty good on the Cherokee, but that has a big fan up front :-)

[ajax_6531]

Per some good old firefighting info (I'm a volunteer firefighter, too, did I forget to mention that?), using a larger outlet side, you wouldn't have to worry about drag on the inlet side since the greater negative pressure would serve to pull more air into the inlet. The size difference can't be that great, though, because you'll lose the effect.