Question for the Aero Experts

[smcdermaid]

The Dec. 6 issue of Autoweek reviewed a new variant of the Mitsu Evo, the "MR". This particular car has what look like vertical shark fins above the top of the rear window referred to as "vortex generators" auto weeek quoting some Mitsu info, they "...divert air down the rear window, ruducing lift by 35 percent." "But you'll have to hit 110 mph to find out."

Sorry, I don't have a scanner to give you an image of this but just imagine modern BMW antennaes in a row preceding the rear window mounted on the roof. It would seem this would disrupt the air at the back of the roof, thus reducing the laminar flow seperation and ensuing lift/drag. Seems applicable to our cars, anyone seen or tried something like this? IMO it's goofy looking but for the racers, it might make some sense. Just wondering...

[atlporsche]

like this one?

sjd

[Porschekid962]

Ever looked out the window of an airliner and noticed the rows of "vortex generators" that usually festoon the wings? Only difference is the ones on airplanes are rectangular, they are used to stop airflow running down the length of the wing.

Never thought I would see them on a car though, kinda funny looking.

[911nut]

Vortex generators are used on racing cars to reattach air flow where seperation occurs. Air which seperates from a surface is turbulent and draggy so it's desireable to re-attach the air to reduce drag.

[kach22i]

Interesting topic.

http://www.bcchapel.org/pages/0003/Vortex%20Generators.html

http://www.microaero.com/pages/v_howvgswrk.html



They look like all they would do is cause drag, guess looks aint everything.

[widebody911]

On a 911, it looks like you'd want them closer to the front of the roof, rather than on the end like the Evo.

[MotoSook]

The separation in the rear is critical...you could probably use the generators at the leading edge of the roof (not a great effect), but you'll still need to manage the flow after the roof (where it's needed most). The air flow in the rear 1/3 of the 911 (above the rear window and engine lid) is something between the "slow" and "stall" conditions in "kack's" picture (closer to the stall condition). Keeping the flow attached or delaying the separation is the aim....the ducktails, Carrera spoilers, etc,... delays separation...

[kach22i]

I found this, look at the VW as well.

Thank you "AutoSpeed".

http://www.autospeed.com/cms/A_1065/article.html

[Dantilla]

I have seen a local guy who races a Targa place these right above the rear window.

Seems to me that if you're concerned about airflow, you would race a coupe, like everyone else.

[Craig 930 RS]

You gotta really be movin' to have Vortex generators take effect - over 110 mph.

Boeing, 14 years wind tunnel ;-)

[cmonref]

PorscheKid962,
Spanwise flow of air on a wing is prevented by "fences", not vortex generators. During the stall, they delay progression of the stall towards the outboard part of the wing, retaining aileron effectiveness deeper into the stall. Vortex generators in front of the ailerons will help this process by keeping airflow attached to the wing ahead of the control surface.

[widebody911]

Originally posted by Craig911
You gotta really be movin' to have Vortex generators take effect - over 110 mph.

I read a couple of links I found on google, and one guy put these on a home built and it seemed like he saw results at speeds much lower than that, like 50-60 knots.

[kach22i]

I found the Dec 6 AutoWeek article.

http://www.autoweek.com/article.cms?articleId=101310

[widebody911]

What's funny is over on the M3 board, today's hot (no pun intended) topic is brake caliper paint.

[kach22i]

Originally posted by Brian K. Haggard
Spanwise flow of air on a wing is prevented by "fences", not vortex generators.

Like the Mig 15, right?

[cmonref]

Yup!

[kach22i]

Originally posted by widebody911
What's funny is over on the M3 board, today's hot (no pun intended) topic is brake caliper paint.

Well............ girls paint their nails, don't they?

[RickM]

Hurry, start making stick-on Vortex generators.....that light up. They'll be the next Ricer hit.

[kach22i]

Originally posted by RickM
Hurry, start making stick-on Vortex generators.....that light up. They'll be the next Ricer hit.

But from what we have read, they really work, so will they sell?

[widebody911]

Originally posted by kach22i
But from what we have read, they really work, so will they sell?

Yeah, but they'll put them on the hood!