Do they work ? Or are they just a fashion statement.
Do they work ? Or are they just a fashion statement.
They work if you are trying to create a vortex...
Seriously though, they do work in some very specific applications.
For most automotive applications they do not do much other than add weight, drag, and more edges to keep clean when washing the car. The primary use is to get flow to transition more consistently.
They generally are intended to delay boundary layer flow separation, to keep the airflow attached to a surface. If used correctly, they are functional. They don't add significant weight, can reduce drag, lift, etc. The devil is always in the details of course.
I've been planning on doing some testing with them to see if I can keep the airflow from separating over the rear window and seeing what that does for the rear wing. The ones I have are just little spikes, not the blobby triangles you see on trucks. Time will tell.
The aerodynamic pieces on the outside of your car are legit pieces that can help when used properly.
The ones that go in your intake are snake oil.
The ones people have on the EVO 8/9 seem to have decent anecdotal evidence that they do decrease lift at on track. People say they notice it for track days but not at slower autocross events. Seems like its a little thing to get that last 1/10th than something that will transform a cars handling.
I do know they work on an airfoil....
I could easily make a set to see how they work...I'm just worried that if they do work, then I'll have to put those stupid looking things on my car 
Maybe if I make them out of something transparent...
So I guess if the aim is to kill lift, this is basically the next evolution of the "rally wing" that creates lift itself, but kills more lift over the back glass.
Edit: Oh wait no need to do an experiment:
http://vixra.org/pdf/1208.0177v1.pdf
Now I just have to find a way to put them on my car and not look like a huge ricer!
Lancer007 wrote: The ones people have on the EVO 8/9 seem to have decent anecdotal evidence that they do decrease lift at on track. People say they notice it for track days but not at slower autocross events. Seems like its a little thing to get that last 1/10th than something that will transform a cars handling.
There is more than anecdotal evidence 
Those VGs were designed with the car though. It's more than a matter of slapping them on the back of your roofline and calling it a day of course. Some good reference points in that paper though. Science.
In reply to Wanderer:
I hadn't seen that source before, thank you for the link. I had only seen guys on evolutionm.net comparing times and handling with and without them.
^You're welcome Lancer, that's one of the short papers that gets the point across pretty well without devoting half your day and figured it especially pertinent to you. 
You need to do some careful analysis to determine if they will work and what effect they will have. Otherwise you may just wasting money and adding drag.
The Mitsubishi Evo paper is a good example.
AutoSpeed has an EXCELLENT series of articles on vortex generators where they built and installed vortex generators and tested them:
Blowing the Vortex - Part 1, Part 2, Part 3, Part 4 (autospeed.com)
Frankly the autospeed articles are not good. Having been in the auto design field for years, and participated in many wind tunnel tests, I can tell these guys really don't know what they are doing.
Wonder if they keep deer away from the road edge better then these;http://www.amazon.com/Custom-Accessories-17380-Alert-Whistles/dp/B000BOALF4/ref=sr_1_8?ie=UTF8&qid=1400810560&sr=8-8&keywords=deer+whistle Sorry couldn't help myself!
The ones I'm going to try are the StolSpeed ones. Much more subtle than the typical stick-ons.
http://www.stolspeed.com/
Ed Heinemann says, "Yes, they do work."
They do work. Common shapes are the delta that Keith posted, and the rectangular ones that are on the airplane wing. As stated earlier, you need to know how the air flows over your car. Place them ahead of the area of flow separation to energize the boundary layer and delay flow separation. They are also effective in sealing the low pressure air in the underbody tunnels/channels/venturi if you have them.
-Henry
olpro wrote: Frankly the autospeed articles are not good. Having been in the auto design field for years, and participated in many wind tunnel tests, I can tell these guys really don't know what they are doing.
but they are on the internets. They must be right.
These guys have seemed to try everything
olpro wrote: Frankly the autospeed articles are not good. Having been in the auto design field for years, and participated in many wind tunnel tests, I can tell these guys really don't know what they are doing.
I would love to see a more detailed critique if you have time to write one!
Those folks relied on tuff tests, using taped-on wool strands to look at boundary layer flow direction. I have seen that technique used in tunnel testing, along with ink flow and smoke. However this doesn't tell you much that about free stream flow, or about drag or lift. One can only speculate from this kind of preliminary information. It might be a good starting point for examinations but "reading" tuff tests are like reading tea leaves. Ultimately, you need to have a calibrated tunnel with an accurate balance to measure forces. Aero changes usually result in TINY differences (which CAN add up - but not always). Some people do "coast down" tests but the inaccuracies and inconsistances are huge. Manufacturers do it properly, in a real wind tunnel with real instrumentation. After-market companies generally just don't have the test resources but still jump to wonderful conclusions based primarily on hope.
In other words: amateurs need not apply. Nothing can be done without investing tens of millions of dollars.
Of this, I am skeptical. olpro, do you have any suggestions for the DIY crowd out there based on your experience? I was going to put tufts on my wing and rear window, then install the generators on one half of the top so I have a direct comparison of the airflow effects. Obviously, the positioning of the generators would be something to play with.
In reply to Keith Tanner:
Make sure the cameras are on the inside. Otherwise, they interrupt the flow you are tring to interrupt.
In reply to Keith Tanner:
When I was active in this area, top tunnels (where one can actually measure the aero results) could be rented for about $500/hour – quite a bit but no where near “tens of millions of dollars”. Frankly, if someone has a for-profit company and wants to market a lot of serious aero stuff for actual money, this is an important thing to do. Is it really asking too much for a company to verify the benefits of their magic parts? The Wright brothers tested their wing sections on a bicycle, using a right-left comparison (force balance) device much like you are suggesting on your wing. So by all means go for it. Just don’t believe that reading the direction of tuffs means more than it does. Tuffs can tell you about separated flow and that can be useful. If you are doing straightforward wings you shouldn’t need tricks like vortex generators in the first place.
What about interested amateurs? $500/hour for a wind tunnel (and travel to wherever said tunnel might be) is not in my personal budget. And there's still an investment of tens of millions, you're just borrowing it for a very brief period...
One thing that I find interesting about the wing is some reading I did years ago about ground effects when it's mounted at 60% of the chord off a surface such as the trunk lid. But on the Miata, you get flow separation over the hardtop. I dealt with this years ago by slotting the rear window, but I think there are more weatherproof options. We did some rough testing years ago that indicated the low mount worked, I'm interested in revisiting. I know about the recent tests of wing height vs drag in Areobytes, but if we only restrict ourselves to slavishly duplicating what we read, we learn nothing.
As for aftermarket companies and testing, you need to look at the economics. $500/hour for development can be passed along if your name is Shelby, but not in a smaller market. So budget is critical.
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