Using aerodynamic vortex generators on cars
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- Опубліковано 26 вер 2018
- How vortex generators can give better flow attachment on cars, reducing drag and sending flow in the direction you want. Note that my most recent aero book (replacing the one shown in this video) can be found here - www.amazon.com/Vehicle-Aerody... or Amazon in your country.
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Julian, what the air tabs do effectively do is improve the handling characteristics of boxy vehicles travel trailers etc. an example; I had a Chevrolet Astro van which is quite boxy and it had quite a bit of play in the steering box and it would not drive straight it would yaw back and forth going down the road and I’d have to saw back and forth on the wheel to keep it tracking straight which was not very relaxing. I plastered the sides and back of the van with air tabs at the very back where the airflow was leaving the van and the van tracked as straight as an arrow! I could drive with one hand! As you say I didn’t see any quantifiable improvement (or detriment) to fuel mileage BUT I would totally use them on a travel trailer and on a tow vehicle at the figment gap to reduce drag between the two bodies. I’d also consider placing them on a deflector wing on my tow vehicle to try to bridge that gap. What they also did very well was to markedly reduce the “push” and “suck” effect when passing/being overtaken by a large semi truck. I wonder if somehow the voticies create a type of virtual tail cone on a square backed vehicle? All I know is they help markedly in this regard and I’d use them for that again.
The guys at Myth Busters did a similar testing awhile back. Their contraption actually lessen the air turbulence at the rear of the roof line on the car used in the test.
Mythbusters is a lightweight TV show. Peer reviewed scientific papers, anyone?
Another great lesson. Thank you so much.
You should check out the aerodynamics of F1 racing very interesting how they dedicate most of the car to airflow and use vortex generators to create the y250 vortex and improve the cars performance
At the ~6 minute mark, where you're discussing the "filling the wake" possibilities, I believe that is specifically for bluff-ended vehicles [ie: the ones whereupon you mostly see the Airtabs implemented] like semi-trailers and motorhomes. The recommended use of Airtab approximately 1 ft in front of the trailing edge of the vehicle, iirc. The irony of imparting better airflow attachment by selective detachment of some fraction thereof is not lost on me...
Very informative! I've installed VGs on multiple vehicles. I've found that obtaining the optimal position(s) on each car is 'half of the battle'. I usually road test w/colored chalk line powder to find the separation areas. My present 'rolling experiment' is a `07 Honda Accord w/"Gas Pods". I see complete downward airflow on all areas of the rear window where it didn't exist prior.
microair01 where did you mount them on your Accord? I have an 07 Accord sedan SE V6 and would love to see where you put them . What gas mileage increase did you see?? Did they help stability?
I mounted them on the roof, about 1-2" from the upper rear window line. I've never performed a definitive MPG comparison, although I do get 30+mpgs on the highway without driving too conservatively. Increase in highway stability is certainly noticeable w/the 'sunroof test'...stability benefits goes away when the sunroof panel is tilted up and return when the sunroof is tilted back down. Needless to say, I rarely drive on the highway with the sunroof open at all.
@@GspeedR Thanks for the reply. How many did you use? AirTabs recommends 3 per linear foot on 4 inch center. Whats your total number of tabs along the rear roof line?? Thanks again!!
Gas Pods are "bump VGs" have a smaller surface area than AirTabs. I used 8 of them spaced apart evenly which was enough to effect the entire roof line.
Vortex generators utilize the same effect that dimples on a golf-ball utilize, except on a golf ball we have to cover the entire ball because we don't know where the front and back are because the ball is spinning, whereas on a car or airplane we know where the front and back are so we can only place them strategically.
Do you think putting these on top of the cab of a pickup truck with a tonneau cover to pull the air behind the cab to attach on the bed cover sooner?
I totally believe in the value of VGs'. My buddy put them on his E55 Baron (light twin engine prop) and they dropped his stall about 10 knots and dramatically helped handling at lower speeds.
As to an auto, I believe that placement is crucial and that putting them on the trailing edge of the roof may not be the optimum location (look at the Honda Legend placement 1/3 down from the rear roof line which makes more sense to me). Most are placing them for aesthetics like the WRX-Sti and the Evos . Until some objective testing is done in an aerodynamic chamber or other facility, I will reserve judgment on their efficacy since although we know they work, we just are NOT sure where they need to be placed to work. Great job on the presentation @Julian Edgar.
The published papers on vortex generators that I reference in my book are good objectives analyses of their use on cars.
@@JulianEdgar True, but where to put them is the real magic. An airplane wing is NOT a car. Your own tests showed that placing them on the Legend trailing roof was less effective than 1/3 down the back glass. Why and how ??
Toyoda has a video showing their VG as installed on their autos.
I can see that promoting better flow attachment would be helpful in stabilizing and directing air to a wing or spoiler. On a that test Prius what benefit would there be? As stated, there is no wake-fill and thus no drag reduction and no improvement in fuel economy.
Any separation with subsequent attachment results in a separation bubble. You don't want separation bubbles from either drag or noise perspectives.
@@JulianEdgar The way to test for drag reduction would be an increase in MPG, which I think you say hasn't been realised. Again, as you stated, there is no wake-fill and thus no drag reduction... nullifying one of your now-claimed benefits. Testing for noise is equally straightforward. Have you done that? If not, this seem to be a wholly academic exercise.
@@SmashGhost The Prius was being used as a test exercise to see if a commercially available vortex generator (AirTab) could actually influence airflow in the way it was claimed to do. It did! (The testing was done 12 years ago.) The Prius fuel consumption was so low to start with that seeing the small variation that would have been created by better flow attachment was not viable - not without testing over thousands of miles, anyway. However, I achieved measurably better fuel consumption on a Honda Legend using the same technique to gain better attachment on a rear window and trunk lid. With techniques developed for the book, I'd now measure the pressure variation on the rear window with and without the vortex generators - but I didn't know how to accurately do this measurement at the time.
these work if you use them correctly, but no one uses them correctly. in fact the way most people use them they actually make the car less efficient in terms of drag.
Hi Julian, do you think these would work effectively when placed in front of a wheel well? I know many manufacturers are using air curtains / redirected air to reduce wheel well drag.
Yes that might work, especially if the face of the wheel is flat. However, best to do an A/B comparison will wool tufts and the vortex generators.
Hi Julian, how about doing an experiment on putting these air tabs in front of the wheel well in your next video? It should be interesting
The VG's on the evo are mounted to a rounded plate with a larger radius than the roof, helping attachment. The rounded plate itself could even wick the boundary layer down, considering it has a smooth leading edge.
I have a side question for you? Are VG's bad for attachment along a flat underbody, I was thinking they could help with attachment but may create turbulence. Possibly placing them 1-2 feet from the end to promote suction?
If flow is separating under the car through a change in shape, I'd expect that vortex generators could improve things. However, the best way to find these things out is to try them and measure the results. Test and measurement is worth a lot more than any guesswork. ( I have a good example of that in the book regarding underfloor vortex generators. The result was nothing like I'd imagined!)
I have a Mazda Miata and being a convertible the interior is quite turbulent. I was thinking about building a strip of vortex generators aft of the trailing edge of the windshield. In your opinion would the reduce turbulent air hooking around the top of the windshield or would it be ineffective because there is no boundary layer past the top of the windshield? Thank you
I don’t think they’d do anything. Use a wind blocker panel behind the seats like Porsche.
Is there a spray-able " micro- vortex generator"?? Plasti dip with electrostatic particles that can be manipulated to self arrange or with a charge . Would a " VG" evan be efficient on a vary small scale?? Just a thought
Vortex generators need to project through the boundary layer, so required size is determined by that.
I have a Lance 1575 travel trailer which has a box shaped rear. Do you think adding these vortex generators to the rear sides and top of the trailer could reduce negative pressure, and how could I go about testing the effectiveness / placement (without a wind tunnel).
I do not think that adding vortex generators to the rear sides and top will reduce drag. Despite lots of anecdotes about VG being effective in this situation, as I cite in the book, I've not seen any formal evidence that's the case. You could test the results by long distance fuel economy or by measuring the average pressures on the back of the trailer. Looking at pics of the trailer, rounding the sharp front corners would be my first step - not easy. Wool tufting the sides of the trailer would show the difference this would make - my guess is that there would be separated flow on the sides of the trailer as it currently is. Lots on wool tuft testing and pressure measurement in my book - www.amazon.com/Modifying-Aerodynamics-Your-Road-SpeedPro/dp/1787112837
@@JulianEdgar thank you for the respond. I'll likely avoid putting them on for now, until I'm prepared to do some testing as you suggest.
Julian, in the states they use something called " trailer tails ". on semi trailers. Why do these work??
Yes, covered in Chapter 6 of my book.
Gotcha, and thanks. Curious as to whether you believe air tabs would help on rear window of Model 3. The rear window is pretty raked .
I try not to guess, but instead test. Wool tuft testing would take 10-15 min to find that out for certain.
Do these stop dirt hitting the rear windscreen on a Isuzu MUX?
Extremely unlikely.
Sir,
In the US these VGs are used on large box shaped vehicles at the trailing edge. Is there and benefit that could be achieved on the front of a box shaped vehicle like a Jeep Wrangler? Could a VG help with the transition between the front bumper, grill, hood and fender flares or would this cause more drag?
Thanks
John
If the flow is becoming separated at these points, vortex generators may help. However, and it's a big 'however', by far the most accurate way to see what actually happens is to test the vehicle when standard, and then with vortex generators temporarily added. Simple wool tuft testing will show the flows. With car aerodynamics it's always better to test, not guess!
lol, need to include an air ionization/plasmafication stage, then use magnetohydrodynamics to create the vortex
What about on the roof of my dual cab amarok to help the air flow over the bed with a cover on it?
No I wouldn't think so - but cheap to try
@@JulianEdgar my biggest challenge, and the real reason I study your work is my wrx powered vw beetle..looking for ways to keep it stable at high speeds as the back wants to take off without a wing like the vw fun cup cars in Europe. Radiator opening at the front adds to the challenge. probably the hardest car to play with..haha
@@mattwalsh1558 All pretty straightforward. Do some testing so you can see what is actually happening, trial some modifications based on that testing, get the results you want then build the real additions. Same as any car.
Back of my carado i339 Motorhome is a flat slab .. I wonder if and where I should fit them..
No where. That's not how they work.
@@JulianEdgar They're used on lorries though.. usually around the rear roof and tailgate sides..
@@mr.d7372 Not by any OE manufacturer though... Check out my other videos on the topic - there's zero technical evidence they do anything positive in that application.
what about the other designs, I can't see anything supporting design principles via sellers.
Not sure what you are asking?
Would these change anything on a van or SUV with a square back?
No
A slightly downward angled spoiler (like you see on modern SUVs) helps the most. The trick is to direct the wake downward smoothly. Tall VGs generates too much turbulence and drag.
How about on the trailing edge of the roof on a pickup truck which has a 90 degree window behind it and a tonneau cover of the back..?
Won’t do anything positive. Why would they?
@@JulianEdgar adds air pressure to the drag volume
@@NwoDispatcher How do they do that? There's not an aerodynamic textbook in the world that supports that theory.
@@JulianEdgar ever seen the rest spoiler of a 3rd gen 4 runner? I own one and the surface deflects air downward to make the rear a "virtual taper". My thought is that the vortexes help make this virtual taper as well. Think of an aerospike missile. It has a truncated nose with a tungsten tipped rod pointing out it's end. This makes the air follow a virtual nose cone path
@@NwoDispatcher You can come up with any personal theory you like, but I go on what professional aerodynamicists say. There is *zero* evidence that vortex generators act as you say they do.
I have a Tesla Y. Where should the VGs be?
In a box in a cupboard.
They should be used in the car like in the intake manifold.
Why?
We just ran AirTabs on and E36 BMW in the wind tunnel. We did only do one run in one location (wind tunnel time is expensive!) but they were terrible. Added a few pounds of drag and less then one pound of downforce (or loss of lift). They are in this video here: ua-cam.com/video/KI1gi9_6WRM/v-deo.html
I don't have time to watch a 20 min video, I am afraid. At what point in the video are the AirTabs, please?
Julian Edgar one of the first runs.
A few things. It's such a tiny wind tunnel that I have some doubts if the results would be valid. However, that said, my more major concern is: what were you actually trying to achieve with the vortex generators? I'd imagine a car like that would already have attached flow down the rear window, so all that the AirTabs would do in that situation is create drag. All vortex generators create drag, and so for them to work, the change in pressures (in this case on the rear window) has to be greater in effect than the drag they create.
Julian Edgar agreed. The car owner wanted to put them on just to see. I figured it would be a waste on a coupe like that and once he saw the numbers we moved onto other things we wanted to test.
What brand?
Airtab
Semi trucks use these to increase fuel mileage.
Very little evidence they do - and some good evidence they don't.
EcoFins have a much better adhesive and less expensive.