Coanda effect

[basjoos]

Here are some interesting articles about using the coanda effect to decrease (or increase) drag. The main trust of the articles is about using it with semi's, but there is also some info about using it with cars. The advantage of this reduction method is that it would take a minimum of modification to your car, just a source of low pressure air (vent fan from a junkyard plugged into your cigarette lighter), some tubing, and nozzles. The trick would be finding the appropriate nozzle locations and flow rates for your car to have the greatest effect on drag reduction. The simplest approach would be to position them to kill the drag inducing vortices that are generated from your "A" columns and from the back corners of your car.

http://www.osti.gov/fcvt/2000-01-2208.pdf

http://permanent.access.gpo.gov/webs...01-01-2072.pdf

[thisisntjared]

very interesting. any cliffnotes?

[basjoos]

This is the type of thing I was talking about. It looks like some car companies are starting to investigate conda effect drag reduction on their concept cars.

http://www.greencarcongress.com/2006...t_altica_.html

[Mighty Mira]

It will be interesting to see if they can pull this off. It does seem like a bit of a cop out for a poor design - it's a bit of a kludge. Look at how big those wheels are, and the chunky mags. Oh well.

[ZugyNA]

Basic

idea

would

be

to

take

some

of

the

high

pressure

air

at

the

front

of

the

car

and

transfer

it

to

the

back?

[Mighty Mira]

Exactly. Transfer it from high pressure regions to regions of low pressure. Of course, if you design the shell of your car so that you minimize these regions, then you won't have to worry about tubes taking up space and fans producing both heat through inherent inefficiencies and also heating up the air by constrictions in the ducting... and also needing to supply a flux of air going 60mph with an area of, say 25 square feet.

Let's do the math, shall we? Say we use a duct with area 1 square foot. That means the air in the duct would have to travel at 1500mph. Another way of looking at it: 28m/s is roughly 100f/s, or 2500 cubic feet per second or 150,000 cfm. Which is a bloody big fan.

[Nerds laugh at me]

I was thinking of something like this the other day. Since I have a hatchback , I have a large wake. I thought of rigging up an electric fan and blowing air out the back.
The fan could be powered by the cigarette lighter, and shut off with a toggle switch at stoplights.

Would something like that just be a waste of time ?

[GasSavers_Erik]

I know this is anecdotal, but I had a really good tank last summer when I had a bunch of junk stuffed in the back of my car so that the hatch was fully open for 200 miles on the interstate at 65-70 mph. The supplemental vents were open (it was hot) so I wonder if it could have been a bit of this effect helping me during that trip.

I have wondered if having my civic's tilt out rear windows open (during the summer) would help or hurt mileage/aerodynamics.

[red91sit]

could act like a gently sloping boat tail at the right angle! But more importantly, it's also a low pressure zone sucking up exhaust fumes... a bad thing...

Also, with the ventilation system open, it would do a very good job of taking the hipressure zone from the base of windshield and putting it out the back

[GasSavers_SD26]

A lot of production sport bikes are using air from the front of the bike to energize the air box with pressurized ram air to develop better power.

Using it at the back? It's still gotta be a big fan.