Compressed air for drag reduction ( Coanda slots )

[aerohead]

Originally Posted by aerohead

I found the reference for earlier work:
"Trapped Vortex Flow Control For Automobiles," by J.J.Cornish,III,Chief Engineer,Lockheed Aircraft Corp.,Marrieta,Georgia division.
Presented,Los Angeles,California meeting,Aerospace Industries Association of America( 100 Wilson Blvd.,Suite 1700,Arlington,VA 22209 USA Aerospace Industries Association ).

It was 1974,not '78.

[Cd]

Phil, what do think of the idea that I posted regarding trying to redirect airflow from my window to the back end of the car ?
I know it probably will not work, but I'm curious to know why.

[max_frontal_area]

more an exercise in relocating air from the high pressure zone.

Larry's Old Volks Home Ghia Land Speed Racer | MyRideisMe.com

i met larry in the early 90s @ el mirage same car, same engine but big aero mod is now missing :[

when i saw it it was green and larry said it exhibited a funny problem.
@ 120 mph the front would begin to lift gently. to alleviate the problem he
ran an 8" wide and 2" thick oval tube which evacuated air from the center of the bottom front of the vehicle (which was causing the lift from air damming up)
through the car longitudinally exiting right behind the bottom part of the rear window. unfortunately he ended up in a higher speed class because of that mod. i dont see the tube installed anywhere, therefore i think he ditched it
in favor of much more depleted uranium. he seems to be running just marginally faster then he did when i met him which makes me wonder if he is running in his intended class again but has now gotten serious about making some power (to overcome the additional loading from the newly added ballast) by chilling his intake air.

i have a sheet of acrylic waiting to replace the heavy glass rear window in
one of my rabbits and am pondering to punch a hole in it for the same effect
but an entirely different reason.

while on the subject of compressed air... thinking of ways to reduce frontal
area on a bicycle type vehicle having pretty much exhausted the possibilities
attention went to the rear of the craft. a bike and rider punch quite a hole in
the air, farings of any kind are not allowed. with no ways of dealing with that
deficiency I mused the idea of intruducing massive ammounts of air to fix and
fill the void left by the bike and rider slowing him...
bicycles are made of metal tubing which could be sealed with some effort
a sudden *outburst* could prove to be quite an aid at an opportune time.
add some artificial methane and sulfer odorants and it would seem like the real thing -
virtually undetectable ;~>

anyone on here that is not math handipacked who would like to crunch some numbers target speed is 60 mph.

[aerohead]

Originally Posted by Cd

If I know from the start that that the results of the testing will be more drag, I won't even waste my time with it.
Will the drag still be worse if I create a smooth channel for the air to run out the back ?
I plan to create a channel running from the passenger side window out to the back of the car. ( I'd remove the passenger seat and fold down the back seats flush.
Since this would be asymmetrical, would this lead to any problems with the test ?

In the real world, this would never be practical on a car like mine, but as I look at cars such as a VW Jetta, it seems that you could create a channel for the air that would be weather tight and would not cause extra wind noise. You could exhaust the air out slots on the back of the trunk.

Cd,sorry for late catching up on this.I believe aspera hit the nail on the head.
Carrying oversize items in my CRX,which required me to have the hatch partially open while strapped securely,rewarded me with a constant flow of exhaust entering from the rear.Nasty!!!!!!!!!!!!!!! .
One might think that everything ahead of the tail is at a higher pressure,but boy could they be in for a big surprise.
I think Hucho would tell you to maintain attached flow while moving your separation point as far back as you can.
If you "open" the body there's a very good chance you'll undo all the good work of the carmaker.

[Cd]

Thanks for the reply Phil.
I decided to not waste my time on the test, even though it would have been really easy to perform.

I do have a question for you though : When you say that you had the hatch on your CRX partially open and got a steady flow of exaust, you did have the front windows open too ...right ?
( of course )

[elhigh]

I was thinking that one way to get some sorta-free air for this would be to redirect the turbo's wastegate. They're talking about big rigs, and they're all wearing great big turbos, so you know they can generate some decent volume. Most of the time, they're loafing along at cruising speed and there isn't much demand on the turbo. I think there's more capacity there to be had, just a little bit of extra plumbing and a few lines of code between the turbo and the throttle position sensor.

Not sure about that last bit vis-a-vis big rigs.

[Cd]

I think something like that was mentioned in the article, so apparently it would work.
I guess the problem would be increased wear on the turbo$ .

[aerohead]

Originally Posted by Cd

Thanks for the reply Phil.
I decided to not waste my time on the test, even though it would have been really easy to perform.

I do have a question for you though : When you say that you had the hatch on your CRX partially open and got a steady flow of exaust, you did have the front windows open too ...right ?
( of course )

Cd,I tried everything I could think of to prevent the incursion of exhaust.Windows-down for dilution was no good.
Windows up,ventilation at 100% outside-air and fan on high no good either.
Nothing seemed to prevent the exhaust from entering.
It's like a VW Beetle/Ghia/Porsche 914/912/911. The air rotates around the back and imparts a ram pressure ( really good for air-cooled engine ).With the body "breached" that pressure is communicated forward towards the ventilation outlets or any region of lower pressure ( especially the A-pillars ).
In the FLOW-IMAGES there is a photo of the trunklid of a 1950s Ford Fairlane with lampblack and kerosene showing the peculiar flow pattern behind the roof.
I believe this dynamic is also present behind the car although there is typically no structure there.

[aerohead]

Originally Posted by elhigh

I was thinking that one way to get some sorta-free air for this would be to redirect the turbo's wastegate. They're talking about big rigs, and they're all wearing great big turbos, so you know they can generate some decent volume. Most of the time, they're loafing along at cruising speed and there isn't much demand on the turbo. I think there's more capacity there to be had, just a little bit of extra plumbing and a few lines of code between the turbo and the throttle position sensor.

Not sure about that last bit vis-a-vis big rigs.

Cornish's paper advocated using the turbo to power a suction pump for slots in the aftbody for boundary layer control.Tremulis spoke of the paper and believed that by now,we'd have cars with typical Cds of 0.12.
I think Georgia Tech is working with this technology.

[vtec-e]

I just had a crazy idea that would have the BLC slots used as the intake to the engine. No good if you FAS a lot though! LOL!!

ollie