diy vortex generators
 

I was wondering today (and I think I have this right) the idea is to get rid of the drag behind the car, boat tail best, kammback another option. However my car is vertical on the rear

New Kia Picanto in Lakeside and Southend | Essex Auto Group

As neither of the above is an option what about creating a vortex behind the car. Could a strip of this across the back have any effect?

Prikka-Strip intruder and cat excluder | Fence spikes | Anti-Intruder

http://ecomodder.com/forum/showthrea...tml#post227421

Random lumps attached to your vehicle are not likely to have any positive effect. Vortex generators used on airplanes cause more drag but allow more effective control surfaces. Vortex generators on cars seem to cause more drag, and they don't have control surfaces.

Yes, it will keep burglars and cats from climbing on your car.

Mo, the only thing you can do to improve your aero here is to make your car longer in the back. It already is a very aerodynamic shape, it is just very short. Doing anything aero in the back part of your car, other than building a plan taper rear extension, will in all likelihood hurt your mileage, or waste your time, money & effort.

http://i54.tinypic.com/2v2w2m9.jpg

MoMoris,

The airtabs inventor actually tested them in a wind tunnel on a hatchback. He showed a 4% reduction in drag. This however was done by a professional and not an amateur.

they have some of the results in a pdf but no photos of the placement http://www.airtab.com/MicrosoftWordHondaWTReportV6.pdf

They can work. You may need a wind tunnel to get it right however.

This thread inspired me to dredge up another concept, I see these were only tested on the sides, and would like to have an understanding of why rounded sides are everywhere when perhaps a sharp transition would be better. If the sides should be sharp for best aero (once the efficiency/handling compromises are understood) then that would seem a less complicated mod or one more likely to give results. A clear strip of plexiglass glued to the rear sides might suffice. Mini-boattail

But we don't know for sure if these specially designed VG would help on the top, the author speculates there.

http://ecomodder.com/forum/showthrea...-te-18133.html

Thats an interesting read and seems that it should be possible then. It was just something I was considering giving a shot. After all we dont truly know untill we try it.

The kia has a curved side as well. I may try the sharp edges idea and extend the roofline for a few runs.

The mitsubishi evos use vortex generators on the MR

JDM EVO MR Taillights Set - EVO 8/9*::*EVO 8/9 Exterior Parts*::*EVO 8/9 Exterior*::*Exterior*::*LancerShop.com | Lancer Evolution Performance Parts



A really good article here:

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



But for now its back to making some more smooth wheels after my first attempt disapeared. the undertray is complete and will be refitted after my master cylinder change. If I see an improvement then im going to remove the coroplat tray and mesh and fibreglass for a better finish.



Edited to add with a daily commute of 150 miles total every little helps

So far, nobody on here has been able to get better fuel economy with vortex generators.
They do help to smooth the airflow, but seem to also introduce extra drag canceling out their positive effect.

Hucho
 

dcb,if you can snag a copy of Hucho's book ( any ) you'll find a very lengthy discussion on edge radii.And I think you'll find that it's not a 1-size-fits -all sort of technology, when comparing squareback,notchback,and fastback bodies.

Mainly because its the look the public has been going for. You have to remember that most people, however simple minded they may be, buy cars based on how they like they look first and foremost and car manufacturers are well aware of this. Plus, if it "looks" aerodynamic to the untrained plebeian eye, they assume it is. Most people assume smooth curves = aerodynamic when we here know this to not necessarily always be the case. Curves are good and have their places - just not everywhere. (I can think of several places I really like curves....hahaha....but I digress.)

I recently put on delta wing vortex generators on a 2005 scion xb with good results so far of course it is very square and flat sided. Ive been using a kiwi scanner to keep track my latest run is up from 29.3 mpg to 35.2 mpg even stopped by two places on the way home I always reset the kiwi and drive the same speed 60 miles per hour, 30 miles each way.

Welcome to ecomodder !

You're one of the first people on ecomodder to actually get good results with them.

Could you elaborate a bit on how many / where you put them on ?
(You'll need a few more posts before you can add links or pics in your posts though - anti-spam measure .
Leaving out the
part and maybe split up an URL will help though ;) )

What was the variation in mpg before putting on the vortex generators ?

Ideally, they should be tested in near-identical situations, under the same driving conditions (speed, distance, previous warm up, traffic density, ...)
That ain't always easy though.

I drive the same distance a day plus the same miles exactly 30 each way from my shop, there is each way a country road of 3 miles for warm up going 20 mph then 35 mpg each way then onto a highway, the speed limit posted is 65, I go 60 mpg each way no variance I do however get better milage to the shop than from w/o the vortex I get 31.8mpg to the shop and 29.3 back home. I live in the ozarks and theres a few hills, anyway with the vgs I got on the first try up from the shop 34.4 mpg of course I was sceptical this is the show me state you know, and I kept my notes in a book and used the Kiwi mpg meter on trip mpg and reset it each time so everything remains the same. well on my way to the shop I got 33.1 mpg I had to go to another shop to pick up something a 10 mile sidetrip, so on the return trip just last night I got 36.1 mpg went by the groceries store and them stopped for gas when I got home because of the stops I was at 35.2 mpg! Ill let you know shortly of any other results thanks again. Oh almost forgot I have 10 vgs on the back on the roof just before the spoiler [now I know why they call it a spoiler it screws up any airodynamics mine sits above the roof line so its more of a wind catcher, oem style of course] the center vgs are at 15 degrees as well as the next outer ones the next are at 10 degrees the next at 5 degrees and then 0 degrees

That's quite promising :thumbup:

there is another example - someone put AirTabs on Honda Fit (Airtabs on the Honda Fit), but still, there is lot of guesswork to put vortex generators right.

I was thinking of doing this to my 1971 Beetle. From what I understand this can have the same effect as a golf ball. With a round smooth surface (like my Bug) the laminar flow detaches more forward creating a larger wake behind the vehicle and therefore more drag. A golf ball induces turbulent flow on the surface, which ironically holds down the laminar flow until further back creating a smaller wake and therefore less drag.

Vortex generators basically so the same thing as golf ball dimples. If placed before the point where laminar flow normally would separate from the vehicle's body, in theory they would hold the laminar flow into the vehicle further back and therefore create a smaller wake and less drag.

Similar effect. Golf ball dimples are omnidirectional, air tabs are not.

Have you thought about the placement?

Yes. On the roof near the rear about 6 inches from the rear window.

http://boojum.as.arizona.edu/~jill/N...comparison.jpg

http://www.gerrelt.nl/roofspoiler/be...unnel_test.jpg

Issac, there are 3 things very much flawed in your "If it works for the Golf Ball Imagine what it'll do to my car" logic.

1st A car is in ground effect, the golf ball is in free air. It makes a very significant difference.

2nd There is a property of a fluid to act differently to one size object vs another. The smaller the item in question the "Thicker" more viscous the fluid seems. The difference the golf ball feels in comparison to a car is not unlike the difference between water and corn syrup. So how the golf ball sized objects react to modifications is going to be different than how a car sized object will react.

3rd your drawing is a drawing and is an exaggerated illustration of how the air is reacting to the 1.7" diameter sphere, while there is a significant difference between smooth and dimpled, this drawing really blows it out of proportion.

Many pages in this forum and else ware in the world regarding the effects of dimples and VG's and even the oft quoted Mitsubishi only shows a modicum of improvement. The Evo involved a very particular set of circumstances and a whole crapload of highly trained engineers and sophisticated equipment to eek out a very slight gain.

I hope you have fun thinking about these things and I really hope it is a primer for you to really dig in to the fundamentals of aerodynamics so you gain a good understanding of what will work well and what will probably yield only a slight gain.

Geez, I just scrolled up and saw the dates....ZomBIe THreAd....ARISE!!!!!

Urrrrrgh Brains!!!

Ok. But what about compared to a wing?

Http://www.aerospaceweb.org/question...tor-effect.jpg

I'm just looking for an alternative to a boat tail.

http://i.imgur.com/bEz6x.png

http://i.imgur.com/ODFr2.png

So I guess it's either boat tail or goat tail. :(

The main problem with a VW Beetle is the steep rear end. And since it's not a box shape is sure would be hard to do an aero-trailer.

Other than that I figured that I could start with a front spoiler and perhaps wheel skirts. The bottom is already very flat, except around the transaxle. I'm not sure how to deal with the flat windshield. :confused:

The main thing I can do is to just drive slower. (Try not to get stuck behind me in traffic :D .)

Beetle
 

The front of the Bug isn't so bad
http://i1271.photobucket.com/albums/...titled1_20.jpg
Sure you could clean up some things,but the lion's share of drag is due to the roofline.
The Herrod Helper of the 1970s helped a little,providing a little centerline flow reattachment.
Ernie Rogers took it a step further with his 'Bug-Wing' rear spoiler.
Anything to fill in the wake will help.
You can see how Kamm 'fixed' this Adler sedan by lofting the roof up to the streamline pathway
http://i1271.photobucket.com/albums/...titled8_15.jpg
If the roof varies from the streamline pathway any at all,you'll have separation again as in this Citroen
http://i1271.photobucket.com/albums/...2/scan17_1.jpg
or Z-Car
http://i1271.photobucket.com/albums/...ad2/scan20.jpg
The doctorate-level aerodynamicists would tell you to attack the back of the Beetle.They've been saying it since 1922.
This VW Student gets to Cd 0.30 in part by keeping to the streamline pathway
http://i1271.photobucket.com/albums/...titled26_6.jpg
For VW's Audi TT,they 'reach up' to the pathway with a spoiler
http://i1271.photobucket.com/albums/...itled12_16.jpg
For a lot more money,VW will push the Audi's roof even higher
http://i1271.photobucket.com/albums/...itled13_16.jpg
For the most amount of money,VW will sell you the 1922 shape!
http://i1271.photobucket.com/albums/...ohead2/209.jpg

Herod Helpers are still available.

http://www.thesamba.com/vw/archives/...rodhelper1.jpg

What do you think about the Ron Lummus Racing Street Wing? It costs twice the price but it looks twice as big.

http://vwparts.aircooled.net/v/vspfi...eet-Wing-2.jpg

Have you seen those spoiler band things on the backs of German Look Beetles? I wonder if those help at all.

http://remmelemotorsport.com/images/..._076-_3_19.jpg

Here's another interesting idea for a Bug:

http://www.gerrelt.nl/roofspoiler/sp...d_8_800pix.JPG

The top is too fast, but Porsche used that to advantage the cooling system. If you modify the rear, that may need to be compensated. Maybe with intake scoops over the rear fender, like Tatra.

The middle half of the bottom is relatively flat. The front and rear quarters aren't, and that's half the length. Again, anything done in the rear could potentially affect engine cooling.

If you look under the front, an L-shaped panel on each side would box in most of the underside, but the lower arms and steering linkage runs through that area. In the back a flat diffuser (it should start at the torsion bar housing) could have louvers oriented to pull air up under the transaxle and down under the engine.

Like aerohead says, the windshield is a good compromise for visibility. The fat-fendered sides and the external hinges and drip rails aren't so hot.

One thing I've been thinking about but haven't documented would be a panel or strip that would replace the side chrome trim pieces, using the same mounting holes, that would follow the front fender contour from the parking light and taper to the door handle area, or curve back down to meet the rear fender over an air scoop. With a boxed-in rocker panel it would mimic the Porsche Carrera GT

https://upload.wikimedia.org/wikiped...ly_2008%29.jpg
https://en.wikipedia.org/wiki/Porsche_Carrera_GT

I've thought about cooling too. I've heard rumors that the Herod Helper hurts cooling. I like the idea of putting scoops on the rear fenders.

I don't know if the underneath is a good place to get air. I've heard of guys taking away the front fire wall tin thinking that it'll get more air to the fan, only to find out it runs hotter that way. The VW design never took air from underneath. It only expelled hot air there. It seems like an air dam or lowered suspension would cause more vacuum under there. That would be good for sucking out hot air, but not for inducing cool air.

One thing I've always wondered is if it would be practical to direct rammed air from the front into the frame tunnel and into the engine compartment.

That would be 1500 cubic feet per minute through a cross section much less than 1 square foot, considering it's full of the shift rod, hand brake cables and gas line. The skin friction and interference drag would choke it.

The louvered diffuser I suggested would only turn over the air trapped under the engine tin. The lower tin would remain (per Bob Hoover) and it offers 1500 cubic feet per minute of activated air to use by any Coanda nozzles that might exist.

Here's my take on the side view you posted. The template is slid back a bit from where you placed it.

http://i.imgur.com/YrMG7.jpg

Here's another picture with the bike rack that I hadn't posted before:

http://i.imgur.com/OHAsi.jpg

The Ron Lummus wing will definitely choke a stock cooling system. It's probably intended for running with the hood off.

http://i.imgur.com/3hEXr.jpg

This is standard race practice. It eventually grows into a rectangular box that completely encloses the engine. But it's for stability rather than low drag, so there is no plan taper, and the side plates are longitudinal instead of tapering off the drip rail.

The rear view out of a half-body of revolution is problematic. I prefer a Tropfenwagen style tail. Here's what happens to the rear view. I made a cone with the same cross-section as the stock back window. The vertex is forward of the rear-view mirror the same distance as reflected to the driver's eye. The intersection with the added tail is flat on the top and bottom and curved on the side as shown, even though the back window's top and bottom are curved.

http://i.imgur.com/YHtUq.png

The visual cone is based on a big back window, even though an oval window is shown.