Help choosing vortex generators

[ConnClark]

The big question is whether he needs all 5 of the vortex generators and if smaller lower drag vortex generators would be sufficient.

[noeryan]

yea. the line of vortex generators is important because the flow seperation starts in one specific area most of the time and the vortices help reduce its expansion across the surface. Placement of them are key though.

[MetroMPG]

FYI, the Mitsu PDF seems to suggest placement is not particularly critical.

I was surprised to read that once you get them in the "general area"...

the optimum method of placement is to arrange them in a row in the lateral direction 100 mm upstream of the roof end at intervals of 100 mm. The VGs are not highly sensitive to these parameters and their optimum value ranges are wide.

[noeryan]

Do you know where the airflow separates on your vehicle? They placed them slightly forward of this region to retard the separation. If you don't test for the separation point and place the VGs too far forward of the point, they will only cause more drag because the vortices aren't doing their job. The VGs create drag while creating vortices. And if you place them behind the separation point you aren't doing anything but adding weight to your vehicle.

I don't want to come off rude. I'm sorry. Aerodynamics is a passion of mine. I want to share it with everyone!

[cfg83]

noeryan -

Originally Posted by noeryan

Do you know where the airflow separates on your vehicle? They placed them slightly forward of this region to retard the separation. If you don't test for the separation point and place the VGs too far forward of the point, they will only cause more drag because the vortices aren't doing their job. The VGs create drag while creating vortices. And if you place them behind the separation point you aren't doing anything but adding weight to your vehicle.

I don't want to come off rude. I'm sorry. Aerodynamics is a passion of mine. I want to share it with everyone!

Welcome to EM! You might have fun with this program. It doesn't claim to be a hard-core calculation engine, but we have had fun wth it :

http://ecomodder.com/forum/showthrea...ator-3709.html

I have Airtabs, but I can't claim they are more than aero-bling :

Where to buy vortex generator fins?

Originally Posted by cfg83

NeilBlanchard -

I have Airtabs. I was worried that I wouldn't like the aesthetics either, so I made them reversible. I used business card magnets :



Then I put a strategic Neodymium magnet in the interior volume :



I haven't lost one since I installed them in March. I only take them off if I am going to wash the car. If I do lose any/all of them, I will probably get more and make them permanent because now I "like" the look.

...

Originally Posted by cfg83

NeilBlanchard -

(is asking me about MPG improvements ...)

Ahhh, I can't prove a thing, . ... Here is what they look like (I still need to add some below the window, just lazy as usual) :



...

CarloSW2

[b939625]

Originally Posted by crexcrex

I can readily see that inspite of countless experiments with vortex generators that this issue refuses to die a graceful death. Voretx generators do not work unless you are a delta winged fighter plane in the attack mode.
Vortex Generators do not work but the subject persists and it is probably due to various companies selling these easily knocked off plastic wedges for ridiculous prices.
Go ahaed and buy these ludicrous items whereas you can be putting the hard earned cash to work by filling your tank.Have you seen any high mileage vehicles using vortex generators? i hardly think so and if they did work i hardly think your vehicle or anyones elses can do mach 1 0r two...................good luck...........your loss is airtabs gain.

because it will take me a million years to explain this all,,,,heres the data !!!! plus its a good idea to research everything that goes with this subject matter..... Fluid Dynamics, Reynolds numbers, Bernoullis Principle, Laminar Flow and so on......

Vortex generator - Wikipedia, the free encyclopedia

(video)

http://www.youtube.com/watch?v=We8LWkqjdX4

(scientific explanation ) http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

(scientific explanation/experiment) http://iopscience.iop.org/1748-9326/3/1/015006/pdf

(good explanation) Vortex Generators for Enhanced Aerodynamics :: Sigma Automotive

Vortex Generator

(scientific) http://www.efluids.com/efluids/pages...G-5001129B.pdf

Vortex Generators - A Neophyte's Track Blog

Micro Vortex Generators - Over 500 Models of Aircraft Certified

Vortex Generators Aerodynamics from Aircraft Spruce

[b939625]

Originally Posted by MetroMPG

FYI, the Mitsu PDF seems to suggest placement is not particularly critical.

I was surprised to read that once you get them in the "general area"...

here are two sites that I ran across that seem to state something a little different.....

Vortex Generator

Vortex Generators for Enhanced Aerodynamics :: Sigma Automotive

[SoobieOut]

http://www.youtube.com/watch?v=MnzSX_6ZQPM

Thought this was an intresting video.

[aerohead]

Originally Posted by Fit

Just an update... after digging around some more, I located this paper votrex generators:

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf

Seems the design of the Vortekz brand generators are pretty efficient as they are simmilar in design to the mitsubishi ones.... then again, of course mitsubishi would say their product is close to optimum

The vgs helped with Mitsubishi's Lancer,as the Lancer has a trunklid for which the separated airflow from the roof can re-attach with the help of the vgs.
The Fit has no 'structure' on which the flow can re-attach to after separating off the roof.
The entire premise of the VG is violated by Honda's architecture.Better to burn your cash on a cold winter night.At least you'll have the benefit of the heat.

[nmgolfer]

Seems some people don't understand what vortex generators can and cannot do.

First... lets get one thing straight... Of course they work!

But what does "work" mean?

Vortex generators are a band-aide for one type of problem not a cure-all. Vortex generators "energize" the boundary layer to help prevent/delay the onset of separation in the presence of an adverse pressure gradient. But they cannot perform miracles and no one should expect them to.

Putting vortex generators on the roof upstream of a typical hatch is a complete waste of time and money. Why? Because even vortex generators cannot prevent separation in the presence of extreme adverse pressure gradients.

So when can vortex generators be advantageous? The Mitusbishi ap. is a good example. There was undoubted a separation bubble at the base of the rear window on that sedan prior to their putting vortex generators upstream. With the generators in place that separation is undoubtedly gone consequently the pressure is higher (Cd lower) with them installed.

The key is that the rear window slope was gentle enough so that there existed the POSSIBLITY that the flow could be coaxed to remain attached. In this case a "band-aide" (vortex generators) stopped the "bleeding" (flow separation). That will NOT the case in all (even most) applications. Its certainly not the case when it comes the the rear window of a fit. (too steep!)

And its not the case in a (I believe it was Sentra) that some one else here on ecomodder tried. Sorry dude... THEY DON'T WORK MIRACLES! The Sentra rear wind0w is WAY TOO STEEP to have any chance of keeping the flow attached. As you learned ... that was a waste of time and money.

Anyway... Frank's right ... spend no money and make them easily removable.

In my own research I learned that the Toyota Yaris Sedan (which I own) had the same Cd as the Yaris hatch (.29)... that made no sense since the Sedan is "clearly" more aerodynamic... now I know why... Tuft testing showed that the sedan has a separation bubble at highway speeds at the base of the rear window. This is not good and something had to be done about it.

A local plastics shop gave me a small scrap sheet of ABS from which I fashioned some delta wing vortex generators (based on a template I found on that other web site clean mpg) I placed these on the glass at the top of my rear window using glue (goop) I know will not come off until I want it to. I then put the tufts back on... lo and behold this time they lay down BEAUTIFULLY. (I don't hear any noise from them either which was one of my concerns). Anyway I know the pressure is now higher on the rear window and trunk (and my Cd is lower) with the vortex generators installed. No I did not do A-B-A. To me the proof of the pudding is in the eating... I only care about my mpg at the pump which is now darn close to 50 depending on how much city driving I have to do.