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.
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.
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.
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 ?
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.