Vortex Generators - hopefully a rational discussion.

[UFO]

Originally Posted by MetroMPG

The deflector on this Gremlin would also "smooth" the airflow over the rear window. And it would increase net drag.

Ahhh, thanks for the memories. I think....

[Pendragon]

Originally Posted by UFO

Ahhh, thanks for the memories. I think....

A 'blast from the past". That car looks to be in remarkable condition.

As I recall it, the rear window deflectors were used to keep the window clean(er) than cars without them rather than any sort of attempt to reduce drag...and then along came rear window wiper systems.

[UFO]

Originally Posted by ChazInMT

OK , How's this for rational.

Whereas my 04 Honda Civic Sedan is a car very likely to benefit from the use of airtabs, the VW Beetle would be the least likely to see an improvement. I believe this is due to the question of simply where on the Beetle would you put the tabs in the huge transition area, then what effect would they have on what appears to me to be a very large area where the air actually does separate from the back of the car. And if you don’t think I’ve given the Beetle aerodynamics much thought, you obviously have not researched my previous postings.

Scientifically, VG’s serve on aircraft as control surface devices, they don't help the plane fly faster or further on a tank of gas.

Rational, but arrogant.

Originally Posted by ChazInMT

I question how something sticking up only 1 inch or so on a car, which is devoid of laminar/orderly flow on its surface due to the unaerodynamic forms poking up everywhere, could possibly effect the relatively huge amount of air flowing within the 24 inches or so of the body which has probably 80% of the effect on aerodynamics, and out to 20 feet for the remaining 20%. In other words, it is like saying you're going to walk up to a 24" hole at the bottom of the Hoover Dam and plug it with a wine bottle cork. To the rational among us, that makes no sense. And some of us rational people speak out when they hear such absurd things. Because that's how we are.

Rational, but rhetorical, exaggerated and unsupported.

Originally Posted by ChazInMT

I hate pseudoscience with a passion, that's where someone takes a small truth and then horribly mixes in a bunch of technobabble to make it sound like it might work. Call me Prejudice if you will, I prefer Skeptic. If you think air tabs might work, than I'd guess Skeptic is a word very far down on long list you would use to describe yourself with Sucker, Gullible, and Dupe being very high on the list. Nothing personal, we all have to be something, it's just how we're wired.

A bit irrational, bordering on personal attack.

Originally Posted by ChazInMT

Airtabs are usually touted as a huge energy saving device and the companies selling them are essentially snake oil/HHO generator salesmen, they are people who probably know what they are selling is worthless, but they look at it as “simply a way to make a living.” They think, “If you wanna be a sucker and not look into what I’m saying, than that’s your problem. If they don’t work as advertised for you, I can always blame it on misapplication on your part.” Yeah, I have a problem with people who think like that.

Very true. I often have issues with gullible people too, however this topic is not purely snake oil as aerodynamics are just that, dynamic and thus difficult to confine to a simple explanation.

Originally Posted by ChazInMT

VG’s don't work 99% of the time. There is not a .01% of the time where VG’s are going to have a vast improvement on the fuel efficiency of a car in the real world. However, 99% of the time they “Can improve efficiency by up to 15%” in ad copy. In the rare instances when they do work, results are minute.

You may be right, on the other hand that number is made up. Nevertheless Metro's testing leads one to think the "theory" of the VGs is somewhat accurate, as he increased his frontal area without decreasing his mileage.

Originally Posted by ChazInMT

Now that's rational, it isn't agreeable, but thats not what you asked for.

I have to admit I am curious about the use of VGs in my application because they are cheap enough to simply experiment, and few people here have played with the New Beetle aerodynamics. I don't expect a big difference, especially after reading the paper on the Mitsu, but it's hardly "Unicorn Corral territory".

[euromodder]

Does Neil still have his bunch of home-made zig-zag tape on his car ?

[Pendragon]

Originally Posted by UFO

<snip>
I have to admit I am curious about the use of VGs in my application because they are cheap enough to simply experiment, and few people here have played with the New Beetle aerodynamics. I don't expect a big difference, especially after reading the paper on the Mitsu, but it's hardly "Unicorn Corral territory".

I am used to seeing vortex generators on the wings of some older design jet wings. In that application they are customarily installed somewhere just before the boundary layer flow separates.

This link has a typical explanation.

"Vortex generators employ the use of small strips of metal that are positioned at an angle of attack across the span of the wings. These strips create small vortices that help energize the boundary layer and keep the flows from separating. Keep in mind, the actual wings produce vortices also, but these are drastically different than the ones produced by vortex generators. These generators work by redirecting the energy of the high speed airflow above the boundary layers into the boundary layer to energize it."

I don't believe that Vortex Generators are a cure all and can see only a limited number of circumstances where they might be of use on an automobile, but it would be interesting to see the results of some experiments or computer simulations (for those with CFD capabilities).

[cfg83]

Frank -

Originally Posted by Frank Lee

Say you do twice as good- .012. Still peanuts.

That's the same as wheel covers :



However, the gain for a wheel cover is predictable because the solution is the same for all cars.

The gain for VGs, however, is indeterminate because you don't really know *where* to put them, unless you are willing to pay for wind-tunnel te$ting and/or commit to a fanta$tic CFD analy$i$.

CarloSW2

[MGB=MPG]

Aerodynamic Fuel Economy Savers for Road Vehicles



i think i may get some and put them on the ford ..
maybe some on the MG hard top too.. but for the MG gonna wait until i run in some rain and see how it *flows*

the black thing on the ford aft top was bought 15 years ago.. . sure does help blow dirt on the back when on dusty roads..
theory is that it directs smooth air from top side to fill *the Vacuum * of the big hole i punch in the air.. thus reducing drag.. maybe works maybe not ..but it sure does change the air flow after the block..

there are many of us started down this long lonely dusty road 50 years or more ago...

Whats your evaluation of that old top duct on the ford ??

[dcb]

Does anyone have any test data of their own? Or a more concrete plan for how folks can determine if there is a positive MPG effect? What is the plan to get this thread out of unicorn land?

I know there are diy 3d laser scanners, and free 3d CFD software, is anyone in a position to lead such an effort (that would have mega aero benefits all around)?

Is there a more accurate way to test than coast down? Group buy for wind tunnel time? Postal scale on a loong tow strap @ 70mph?!?

Any ideas at all? Is it worth the possible mpg gain if there is serious work involved?

[Frank Lee]

Originally Posted by MGB=MPG

Whats your evaluation of that old top duct on the ford ??

Take it offa there, it's not doing anything good, not even keeping the back window clean.

[fjasper]

Originally Posted by ChazInMT

"Conversely the new DIT2-wing technology makes use of the compression ratio similar to the piston in your engine equaling a 10/1 compression ratio because the piston is housed in a sleeve. Likewise the DIT2 turbine is housed in a sleeve, which is designed to take full advantage of super low-pressure vortex action, which in turn generates an implosive thrust in opposition to explosive thrust. The thing to remember is that there is more energy in this pulling force than there is in brute pushing force."

This made me laugh so hard I almost choked!

We should have a contest (in the corral, obviously) for the most scientific-sounding, vaguely plausible, complete hogwash aerodynamic/mpg sales pitch. I'm thinking of two classifications: Found-on-Internet and Purpose-Built.

Winner receives a coupon good for 50% off one of my $29.95 turbine-action axial vortex laminar compression fuel conditioners. By aligning the quantum spin of the fuel molecules, it creates improved laminar flow from the fuel injectors which makes the O2 sensor send a signal to the ECU activating the hidden "100mpg" fuel/ignition map that Big Oil doesn't want you to know about.

100% guaranteed to cost you only $29.95 plus shipping. If it's not working for you, you must not be believing hard enough. Any resemblance to a cheap generic fuel filter with glitter in it is completely coincidental.