The truth about aerodynamic vortex generators on cars
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- เผยแพร่เมื่อ 19 มิ.ย. 2024
- How do vortex generators work - and what can be achieved by their fitment? It's probably a lot less than you've been told. 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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This is the "golf ball dimple effect" as applied to a car, it just has a different name "vortex generator". On a golf ball we cover the entire ball in dimples because we don't know where the front and back will be since the golf ball spins, but with a car or airplane we know exactly where the front and back is, so we only apply it exactly where it's needed, in this case near the back of the roof.
Additionally the dimples only work over a specific range of speed. Above or below that speed drag is worse.
erik u need to mention the vortex generators work only for a short way
I’ve been watching your videos about vortex generators for 2 months before I have cut old canards into tiny makeshift vortex generators for my motorcycle 3 weeks before Christmas 2021.
Wooow, they do work!
I no longer feel too much air drag. I put the tiny vortex generators 3 inches behind the biggest bends on my motorcycle’s fairings and I have put tinier vortex generators on the sides and on the temple of my helmet. My helmet is now less shaky whenever I run past 60 KM/H. 💚
Well hell, sure wish i had known that!
Even though your not a aerospace engineer, you have a very well put together base of knowledge and I’ll definitely love to hear more. Keep it up and I’ll keep following.
I have your book Modifying the Aerodynamics of your road car and found it very useful. The trouble with these commercially made vortex generators is that the edges are rounded. Even the ones fitted by car manufacturers have rounded edges, both for ease of manufacture and painting. To create decent vortexes you need sharp edges. I use the same VGs but sand the edges flat to give a sharp 90 degree angle which makes them much more efficient. When playing with aero, especially with small things like VGs, the small details matter.
Are you modifying the Y shaped vortex generator, or a different style? Can you post a short vid???
Thanks for sharing the info. I'm looking for ways to improve the fuel economy on a jimny, it's a total box haha so I'll look into this
What a fascinating channel! I have a Ram 1500 and work on Helicopters so i have a pretty good understanding of Aerodynamics (practically at least) from work and an interest in drag reduction thanks to the truck!
My latest book covers drag reduction on pick-ups - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
Question. In the cases where you mentioned the vortex generators were ineffective, the cars were all 2 box designs (hatchbacks). Correct me if I'm wrong, but from my understanding, in 3 box design vehicles (sedans), flow separation occurs the most prominently near the rear windscreen (aside from the wake, of course). So doesn't it make more sense to use VGs there (like in the Mitsubishi)? Reason I ask is, VGs so close to the wake have very little scope to keep the flow attached to the BL, when the angle of the body contour is so steep.
Well done ! Appreciated. 4 years ago. Liked and subscribed.
Welcome!
Julian, brilliantly explained video however I have a question not touched on in the video.
If the boundary airflow is at low speed on the trunk lid/rear of the car, where theres no attached flow is it possible the exhaust fumes from the tailpipes could rise up over the rear valance, up and around the rear bumper, up over the rear light panel and in to the gap between the rear light panel and the trunk and exhaust fumes enter the trunk/boot if there is no seal around it?
I cant see it myself, it just seems to far a journey and against "flow" for the fumes to not be carried off in the wake of the moving vehicle.
My favorite use of vortex generators is on the floor of the rb19 f1 car which seem to allow them to have a lot of volume without stalling it
Hi, first off all, thanks for the great content, you really know what you're talking about 👍
I got a theory in my little small mind, I'm running a van, vito 639 body. It's square in the real, and has something like 1.5m X 4m roof area. as you been telling there is lift on the roof. My theory is that if you build a second roof or a chanel on the roof (depending on how you want to call it) to chanel the low pressure air from after the Windscreen all the way back to the car. The theory is that the low pressure area will pull the underside off the second roof with the same force as it pulls the car normall roof and the forces cancel each other if the chanel is high enough. There should bee less or none vacum on the top part of the second roof so in theory you should get ride off lift from the roof?
Maybe make it a real chanel and get some off the real end under pressure to lower the pressure on the windscreen 🤔
I would love to test this out from scratch Plywood that I'm getting my hands on. Let me know your thoughts if it's going to be total waste of time?
All the best and keep up the great work
The van probably doesn't have much lift, but the best thing to do would be to measure how much lift it actually has before making any changes aimed at reducing lift! Measuring lift/downforce is easy - covered in my aero testing books.
Very very good explanation
Thank you!
What about adding vg on the rear side panels to reduce wake And or to increase stability in cross winds i. e. When driving in the wake turbulence of tractor trailer . ?? Just a thought thanks for sharing your tremendous knowledge . I truly appreciate your testing based approach and thanks Again you've saved me alot of time and failures your book is in my Amazon cart. I feel plain guilty for how much you have taught and saved me to just say thanks
I don't think VGs will do anything at all in that situation. When my book arrives, read the chapter on gaining less left and more stability. Thanks for the praise!
My airplane uses VG and it helped a lot. They are most useful when placed in an increasing pressure area. Like near or just after the high point of the airfoil. For a car they may work better when placed further ahead in the attached flow area .Not in the dead zone of the rear window .
Aircraft are completely different to cars. In fact experiment shows they work best on cars in the positions described in this video.
So is the a minimum distance you need for these to start working or the farther forward the better
Hello sir, first of all, thank you so much for such informative content.
Though I have a question, I didn't get why exactly do I want to reduce base separation to increase fuel economy?? How do I get better economy by getting more pressure on the car's rear end or how it does generally gives a better performance?
Thanks in advance and again thank you for sharing your knowledge.
Its because of drag. If you have low pressure behind the windshield it will create a suction like effect, which will require the car to put more power to push it ahead. If the flow separates at the end of the trunk lid in stead of on the top of the windshield there will be less wake and less drag, thus requiring less energy to push the car ahead
They are advertised for trucks. Have you done any “wake” testing on pick-up trucks with shells, or on big commercial box trucks, or box trailers?
The book is on road cars and so I haven't covered anything on trucks. The book covers some work on pick-ups, although not with vortex generators. Rounded front corners and sharp trailing edges would improve the drag of many vehicles of the shape you describe.
I have old Lada 2105 with "VFTS" bodykit. It has similar type of rear spoiler like that MX5. I fitted some vortexgenerators under angle to the roof edge. On highway speeds it does feel like less lift as rear end feels more planted.
I wish I can import the Lada 2105 or 2107 (they look the same) or even the Lada Niva 4x4 to the states
or the Lada Samara (that looks like a hatchback)
@@Jeremy_Hill_2020 i believe there were some exports going on during 80s, maybe you can find 1 from Canada or south America
@@Jeremy_Hill_2020 i checked, about half of produced cars in 80s and 90s got exported out of USSR to about 100 different countries
7:31... It was my understanding that, on a square back, the VG's need to be set 20-30cm in from the trailing edge; and that it is how Airtab recommends they are installed on square back vehicles. By doing that, the vortex stays closer to the boundary later, and the sheer nature of the vortex creates a cleaner seperation from the trailing edge of the vehicle.
Yes, AirTab says lots of rubbish unproven in any technical literature of the last, what, 40 years?
Hi Julian, would you advise putting airtabs on the back/trailing end of a motorcycle topbox luggage to reduce buffeting and/or drag? And how about small VGs, similar to Stolspeeds, on the windscreen to reduce helmet buffeting? What angles would be suitable for either, assuming that they will work?
With stuff like this I don't guess. I experiment and see what happens. Vastly too many variables to be authoritative in any advice.
@@JulianEdgar Thanks for the honest answer.
I asked this because I saw Airtabs being advertised as fuel savers for trucks and RVs. And also this article: spinoff.nasa.gov/Spinoff2008/t_3.html
So I was wondering if a motorcycle box, which is basically a similar box shaped object, would benefit from having a couple of airtabs along the top, towards the rear, to smooth out the airflow.
7:42 Both cars you refer to have very clear separation edges. This should mean that the airflow separates immediately after the vortex generators. The result may be different if they were mounted on a car with no separation edge. The airflow would probably stay attached for longer thus delaying separation and increasing flow in to the wake zone.
But as you frequently point out, testing testing testing...
Thanks for very good and informative videos!
The separation edge reduces drag - you do *not* want airflow wrapping around the edge into the wake. If, as you suggest, vortex generators were used without separation edges and delayed separation, then drag would increase...
Yes, that makes sense. Thanks for the feedback. 👍🏻
I am thinking about putting these on my pickup and trailer to help with trailer wander and fuel mileage. Will they help?
No I wouldn't think so. However, some simple testing with wool tufts would show what is actually occurring, and then you could have a much better idea of whether they could make an improvement and where they should be placed if that improvement was to occur.
If you have a roof bar, can we add a vortex generator infront of it to reduce the pressure acting on the roof bar and promote more air flow under it?
Did you ever try that out??
Sir, very good video. One question I have for you: I purchased some shark fin vortex generators for my Mitsubishi. You had mentioned in your video that placing them direct longitudinally serves no effect, would you suggest sticking them at certain angles as shown in your video (the yellow Mitsubishi example) ?
Thank you-
Don't guess, test. Just do some tuft testing with the VGs set at different angles.
Ahh, not the answer I wanted, but I guess it is the answer I needed. Thank you Sir.
@@tylerjohnson6658 Shouldn't take longer than an hour, and even easy to do alone (just look at the tufts in the rear vision mirror.)
Ok great to know!
Thanks I have a minivan with a mostly square back. I see from your presentation that vortex will not improve its performance.
Hi Julian, thx for the nice video, I'm looking at those Vortex generators recently, I have a question to ask about, what if you turn around the Airtab on the back of the car where the air separation area, will it give better airflow or attach effect? I do an experiment by using a hairdryer to blow on the pointed end of the Airtab, with attaching the tissue on the hairdryer, I immediately find out the air has been pulled downward, but if I blow it in opposite direction, the tissue is pulling upward. On Airtab instruction, they suggested to attach it on the very end of the trailer, I reckon it's for ask the air "jumping" better from the gap between the tractor and the trailer, so they should generate counter-rotation vortices, but if on the sedan or racing purpose, we're looking for more attached flow for the rear wing to get more downforce, so we should turn it around ( the pointed end towards the front ), could you give me some ideas on it? I'm not sure that I'm making the right conclusion. Cheers
Use it orientated as the manufacturer suggests, to achieve what is covered in my video. If you chose to use it backwards, its efficacy is up to your judgement!
@@JulianEdgar If I use it in backwards, what kind of downside will be? Like does it will increase the drag?
I don't think anyone could say.
@@JulianEdgar Thx
I have a question... the cfd model around 5:50 shows a much higher pressure region on the trunk lid as compared to the right side without vg's. I was under the impression that fast moving air is inherently low pressure. Would this mean that we actually have a significant increase in boundary layer separation on the vortex generator side causing a swirling, low speed/high pressure zone?
No, I think it much more likely that the vortex generators are doing what they should do, and that is promoting flow attachment. The attached flow has a higher pressure than the separated flow that was occurring prior to fitting the vortex generators. That is, pre vortex generators, there was a partial separation bubble on the trunk lid / lower part of the rear window. Note that, technically, you'd expect attached flow to slow at the rear window / trunk lid transition, so increasing pressure - but you need attached flow to do that.
@@JulianEdgar I get it! So basically anywhere with a sudden change in direction is going to exhibit a high pressure area... like the cowl that's between the hood and windshield. Now I understand why gurney flaps work on wings. Same concept.
@@MRMIKE276 No, a sudden change in airflow direction is very often associated with *low* pressures! Maybe buy and read my book?
Hi Julian. I enjoyed your video, thanks. Have you done any work on RV's and/or Caravans with great big square backs? With so many grey nomads (like me!) doing lots of km's around big distances in Oz, there is a great potential for fuel savings???
Hi Ken, I think that there's huge potential for reduced drag from caravans, but it really needs a manufacturer to get on board and do some proper development. At minimum caravans need proper rear separation edges and radius'd upright front edges.
Thanks Julian - something to work on.
It is well documented almost everywhere that AirTabs greatly help Fuel Economy, and more importantly, handling, on RV's and Semi's. Anything with a great big square back should have AirTabs. AirTabs and Scrubblades are a MUST for Semi's and RV's.
@@booradlly Do you know of any peer-reviewed, technical papers that support what you say? I don't know of even one - and if they worked, there would be lots! Without that type of evidence (as opposed to anecdote) I am quite unconvinced.
Julian Edgar Found your video while researching generators to reduce motorcycle windscreen buffeting.
To chime in on this discussion, it will be interesting to see the final aero design of any trailer that goes along with the Tesla semi as drag would have a dramatic effect on range.
I'm hoping for your thoughts on this one!!!!
.......what do you think of how a Delorean was designed?
I don't own one, maybe some day, but I was think how air flows over the rear, & also thru the vented engine cover (does it flow out, or vent in & under the rear?) & how those rear loovers work in air flow???? Do they extract air out of the engine compartment?
Would VGs work anywhere on that brushed stainless work of art?
I wonder if the brushed stainless acts as some linear micro air straightener!!!!! LoL?????
I am afraid that guessing is pointless. I don't guess, I test.
sunshine state plates on your Honda insight?😳 you're in Florida Mr. Julian? me too!💪
Nope, I was then in Queensland, Australia.
@@JulianEdgar 😅 i saw that it said Queensland in another video. that's cool we live in sunshine states in different hemispheres
Hi Julian...What is your thoughts of using vortex generators across the roof of my car to stop the rear from getting so dirty so fast? Would they help?...Chev HHR. Thanks.
It won't do anything. The near vertical rear window is in the wake, and the vortex generators won't change that. It's possible that a large horizontal extension mounted below (not above) the glass may stop some of the recirculation bubble and so change the flow pattern - try it with a temporary piece of cardboard and see what happens.
@@JulianEdgar Thanks very much.
Good morning sir, I was looking at using vortex generators as a solution for anti-buffeting many of us track racers experience in our cars at high speed. I was thinking of using some vortex generators on the front a-pillar to redirect air around the sides of the car and our windows, which we must run down at all times. Thoughts?
Try it and see. No point in my guessing. In car aero, experiment beats guesswork every time!
Would the magnus effect created via a rotating cylinder have the same effect as vortex generators? It doesn't sound practical, but it sounds like it works on paper.
Yes possibly. Appears to give better flow attachment on aerofoils.
Julian, Would appreciate a link to that paper to the Peugeot experiment if you get the chance. Or if someone else can link me. Cheers
All references are in the book
I own a bus, a Crown bus, which is quite nicely curved on the backside. I had always believed that this was good for aerodynamics, but now I'm not so sure. I wonder if some vortex generators across the top and down the sides might help the flow stay attached a little further around the curves of the sides and top and onto the back, and could this make any meaningful difference in drag and it's associated fuel costs?
Keeping the flow attached around rear curves will make thing worse! You need separation edges.
What would happen if vortex generators were added to the trailing end of the underside of an airfoil such as a spoiler on a trunk lid?
You just created MORE drag for no particular gain
is getting vortex generators for the car stupid on a impreza? will it benefit or? I mean I think ill do it halfways for the looks since I like the look of it. its the impreza wrx from 96
With car aero, I don't guess - I test. You should do the same.
What about putting vortex generators along the bottom side of the rear bumper/fender???
Why?
Would these work on a circle track car that doesn't have a rear window? Thank you
I don't know, but cheap and easy for you to test.
@@JulianEdgar thanks. I thought the same thing. Cheap enough to try
Is there any work to do to improve aerodynamics on a VW bug 1303? What should be considered? Thank you
Do those VG's could work? Where to put them?
Forget vortex generators. A spoiler creating earlier rear separation may be beneficial - Page 140 of my book -www.amazon.com/Modifying-Aerodynamics-Your-Road-SpeedPro/dp/1787112837
what would be a good position to place vortex generator on a cube like a kia soul?
No where.
@@JulianEdgar thanks 😂
I have a race truck that is enclosed over the bed with a sloped back rear window and a wing. I’m sure there is separation off the roof but where?
Just do some tuft testing and find out!
hi sir.. i have a Small hatchback something like a honda Fit. do u think vortrx generator can help improve stability on high speed? i would like my car to feel more planted on the road when im driving 80, 90 mph. now it feels like its gonna lift off when im hitting those speeds. and where should i place them?
Vortex generators will do nothing to reduce lift. A full undertray would make a huge difference, and a good rear spoiler a small difference.
@@JulianEdgar thank you so much
Use lowering springs and put on a front lip spoiler. It will help.
Ducktail spoiler will add more downforce to the rear.
So if i go with vortex generators on my electric car (Nissan leaf). I will normally be driving at highway speeds. Would it be benificial to buy some small vortex generators since it will be at high speeds? Or is there something other i should consider first
Did you watch the video? Why would they do anything at all on a Leaf?
Mate its a leaf 🤣🤣
When aiming to reduce the wake, the manufacturer for AirTabs says to apply them to all of the edges or at least the top and the sides. Which to my layman's reasoning makes sense, the vortices would more or less lengthen the wake, but with the angles being softer less air is being sucked in. Like instead of a box with 90 degree corners it becomes more of a curved pyramid. Only adding vortex generators to the top would just cause air from the sides to get sucked in to fill the void left by the air that's no longer coming from the top.
I doubt it'd get any sort of benefit on a car like the Honda Insight, because that was designed to pretty much be as low drag as possible. But it could work pretty well on a Ford Transit or a Renault Kangoo.
I've not seen any independent evidence that vortex generators are effective in the way you describe. On Page 145 of my book I discuss an interesting paper that shows how *ineffective* they are in decreasing drag by modifying the wake.
Yea, this test of his is flawed. Everything you describe make perfect sense. There's volumes of independent evidence that VG's are effective in the way you describe on Semi's and RV's. Are they also effective this way on Sedans, who knows, but the principle is sound, his test is not for the reasons you describe. The only question is, is the sedan body so small that the effect is negligible. If only someone would test this. . . .
@@booradlly If you can point me to SAE-level engineering evidence that vortex generators do as you describe, I'd be very interested. When I wrote the book, I couldn't find even one peer-reviewed paper that supported this. In contrast, I found one paper that proved that they *did not* work in this way, and I also communicated with the head of aerodynamics of a major car company who stated that in his wind tunnel testing, they did not work in this way.
@@JulianEdgar I have an issue with your wording not your substance. The issue is in your response, "car company".
There is detailed analysis on VGs for both Semi's and Airplanes. I could be wrong, but I don't think you would dispute this.
There is no analysis on Cars for this topic, as you stated.
What Poupon is saying, and I agree with him. The study you found fails the scientific method sniff test. i.e. its not SAE level.
@@booradlly If you have evidence (at the level of a peer reviewed engineering paper) that vortex generators work on reducing wake drag, can you please direct me to it? I'd honestly love to see it, because I couldn't find any. (Aeroplane wings are not much relevant here.) Re cars, the fact that OE manufacturers are not using vortex generators to reduce wake drag tells you all you need to know about what their testing has found. So I don't think that vortex generators are effective in reducing wake drag, but if you are convinced they are, why not try it and see what the results are?
What do you think the simplest method of reducing wake drag is on a vehicle such as a 955 Porsche Cayenne?
Are front wheel wells a high or low pressure zone on production vehicles? I have had a hard time finding a definitive answer to that.
There is no way that I am aware of of easily and effectively reducing the wake drag on the Porsche 955 Cayenne. (If there was, Porsche would have done it.) Adding vertical rear separation edges may make a fractional (ie unmeasurable) reduction to drag. A horizontal extension half way down the rear door may increase pressure very slightly. An undertray would likely achieve far more in drag reduction. The best way of finding out the pressures in a wheel well is to directly measure them - technique covered in my book - www.amazon.com/Modifying-Aerodynamics-Your-Road-SpeedPro/dp/1787112837. I say that because the pressures will be dependent on a bunch of things - like how much air is exhausted into the wheel wells from things like oil coolers, intercoolers, etc. That said, on the cars I have measured, the wheel wells are a lower pressure area.
@@JulianEdgar I came across your video while thinking of solutions to keep the rear of my SUV (which happens to be a Cayenne, so I latched on here) dust-free for longer. I'm not so concerned with drag if it's tenths of a mpg, but do you think vortex generators would help keep dust off the rear of a boxy car?
Would you consider create a digital version of your book? I'm from a developing country and I would love a cheaper version of the book.
No - it takes only hours before it is pirated.
@@JulianEdgar Sorry to hear it, but that's a fair point. Maybe in the future I will acquire the book, for now I'm going to enjoy your videos. Thanks a lot for the content.
Can you use Vortx generators above the windshield, but in front of a roof rack to reduce roof rack noise? Instead of a air screen?
Likely to make things worse, but 10 minutes of testing to find out.
@@JulianEdgar thanks for response!
I’ll see what happens
I'm curious how something like a early Corvair does in a wind tunnel? It's not the drag I'm interested in it's what the engine itself does to airflow since it pulls a significant amount of air in through the top and shoots it out the rear where the wake would be.
Easy to measure on a real car - just measure the base area pressure on the road with / without the cooling airflow. All covered in my most recent book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8
@@JulianEdgar might need to look at that book at some point, The Corvair is a weird case because it has a rear mounted air cooled engine. The cooling air is pulled in through the top of the engine bay lid so it probably does some interesting things to the boundary layer.
Not really that weird - Volkswagen Beetle, Porsche 911, Tatra. I cover the change in cooling drag on the Beetle in my book on the history of car aero - www.amazon.com/Century-Car-Aerodynamics-science-airflow/dp/B095RLP52B (and the Corvair in my book on the history of car suspension - www.amazon.com/Car-Suspension-over-years-handling/dp/B09CRNQB9P)
@@JulianEdgar I guess I meant in the context of modern cars, thanks for the links.
How about on rv type vehicles that are square?
No independent testing shows they do anything positive to reduce drag on squarebacks. (And some testing shows that in fact they increase drag.)
Explain the comparison between car with vortex generator and car without vortex generator with represention of pressure distribution
Yes, done in the book.
@@JulianEdgar thanks
Do you think vortex generators can quiet the sound made from LED light bars mounted close to the roof?
I doubt it, but easy enough to try it and find out.
this video gave me a true "ah ha" moment with the vortex generator.
the flow separation thing makes perfect sense now.
Great!
Can you put vortex generators on a 08 Ford ranger pick up? Where would you put Vgens on any pick up truck. Can any body answer or done testing?
You can put vortex generators on anything you like. But what are you trying to achieve?
@@JulianEdgar well, from what little I understand they will reduce drag so . For my ranger I'm looking to get more fuel efficiency. Less drag = more fuel economy.
No I don't think that they will achieve any measurable gain. On a pick-up, far better to use a sloping canopy (topper) where there *is* clear evidence drag can be reduced on pick-ups.
@@JulianEdgar ok, awesome. BTW I did enjoy your video, I came across it cause I was searching for video on article about creating vortex with electricity on an airplane wings. So anyways Thank you very much from Rainy Eugene Oregon.
th-cam.com/video/KwcBFEzbQmk/w-d-xo.html - This video shows a good topper for a pick up.
So this wouldn't have much effect, if any, on a hatchback, right?
Right.
Sorry man but don't votex generators increase the lift by reducing drag acting on the boundary layer, thus making the air flow faster on the surface , thus reducing the pressure acting on the surface ??
No they don't. But if you can point me to a professional aerodynamic reference book or paper that says that, I am happy to look at it.
Julian Edgar hi julian , i checked again and I was wrong :
Downforce is enhanced if there is a presence of a spoiler , as by the evo. Now I understood the image on your video.
An enhanced lift is only obtained in the absence of a spoiler , thus by making the air pressure low on the surface of the car without passing under a spoiler wing.
How about pick up truck vortex generators to trailing edge of roof.
No
where can I get the mitsubishi tech paper, please ?
It's available online. Do a search under: Koike, M., Nagayoshi, T., and Hamamoto, N., “Research on Aerodynamic Drag Reduction by Vortex Generators,” Mitsubishi Motors Technical Review, 2004, No 16.
@@JulianEdgar I found it, thanks a lot, I just came across your videos, sir. expect a lot of questions from me, I'm a Mechanical engineering senior under graduate, and interested in everything automotive related.
Just so you know, I usually answer questions only from people who have bought my books and have a specific, page-referenced question.
@@JulianEdgar Thank you for answering, Mr.Edgar are your books available in ebook or pdf format ?
@@osamamaddani No, only as print copies.
I think normal cars are already processed in windtunnels and optimized for there purpose.
Thanks for writing a book on the topic when fuel prizes are sky rocketing.
But vortex generators to normal cars far below the speed of sound will not generate as you said any benefit to the fuel consumption .
The shark fins looks great,but thats only that.No benefit at all above that.
I have a 1987 Nissan EXA (Aussie) that if you look at a pic of one it'll show you how useless vortex generators on this thing would be as there's no curve from the roof to the rear windscreen anywhere, just a sudden cut, but it does have a boot lid. What I notice after driving the car in the wet, when I have my driver's side window open about 1/2 inch, it creates a vortex that forces the air onto that side of the boot lid, as evidenced by the blasted water droplet trails there.
Opening the passenger side window does the same, but there'll always be the dull turbulence in the middle of the rear window and part of the boot lid, that can't be helped. Kind of sure in this regard I'm reducing the size of the wake (still air) behind the car as I've got 2 large vortices clearing out this area. Fuel savings? Unknown as I never get a good chance to test these kinds of things accurately. Thanks for the vid. Good stuff.
Interesting, but vortices of that size would create a lot of drag - far more so than offset by any bootlid attachment.
@@JulianEdgar - I don't doubt that, as injecting energy into anything requires energy, likely more so than lugging around a bubble of still air. Really the best way is to teardrop the back of the car but ugly and impractical.
In any case air coming from the forward vents (and any other leaks) go out the windows to create the vortices, but I'm not sure if that would offset anything by a huge margin.
But I dare say the EXA's bootlid "spoiler" is just for looks. The trailing edge points downward giving me the impression it's to keep dust off the tail lights, but in practice this is near impossible as the rear screen rake is too steep to provide any airflow.
@@revolution3395 Easy enough to measure the actual change in drag on the road / whether the spoiler is in attached flow (etc) - covered in my aero testing books.
@@JulianEdgar - Oh, just by observing water droplets on the bootlid NOT being blown around in any significant way with the windows shut shows me the spoiler's definitely not in attached flow and completely useless.. ☺ The side windows when closed get a blast of air right where you need it from the mirrors to clear water from the glass, as I believe were their original design intention. They make a lot of wind noise.
The front left wheel arch _by the manufacturer_ has a large gap in it coming from the air dam, but the right doesn't for some reason. I filled any wheel arch gaps up with aluminium plate and from that extended this down a further inch to create spoilers in front of the tyres as all cars have now. High speed stability improved with this, probably reducing airflow out of the wheel arches.
Also filled in the "diffuser area" as it was just completely hollow around the spare tyre forming of the tray. Air was just getting caught up in that huge hollow space. I still need to fill the underbody but that's for another time.
You seem to have things well covered in your vids so I'll go buy your book. No doubt lots of gaps in my knowledge although aerodynamics is one of my fave subjects.
@RevOlutiOn Your other post comment seems to have disappeared but yes, extensions on the roof / pillars would probably reduce drag. See also th-cam.com/video/SYLBMJKR91w/w-d-xo.html
Do vortex generators increase fuel efficiency?
Depends on the car and where you put them.
Hi @JulianEdgar. There is a TH-cam video ( th-cam.com/video/lHVEgGXoV4k/w-d-xo.html ) showing wool tuft testing of an "eBay style" vortex generator with fins longitudinally aligned to the body of the vehicle, not splayed out, exactly like you warn against.
The vehicle is tested before the longitudinally aligned VG is fitted, showing a separation bubble in the bottom centre of the rear wind screen. The LA VG is then fitted and wool tuft tested, showing all tuft ends completely stable. Indicating the longitudinally aligned vortex generator promotes attached flow where there otherwise wouldn't be. I would love to read your commentary on this phenomenon.
Yes, they're working well. Obviously the airflow on that car is already diverging from the longitudinal axis, so the VGs can be aligned like that. On other cars, that may not be so.
i am the first one to view this video wow....
Isnt it called Boundary layer ?
Yes. What did I call it?
@@JulianEdgar welcome to the internet. 3sec memory.
Can i ask you, should you know.... what is happening between the water hull deck and sail? A complicated question considering boats aero is its power source and the angle changes..
Also i understand how the sail works. I want to know if the impassbilty of the water combined with the decks flatness is a horrible loss on something that needs all the energy retention it can get!
@@Lesserthannone I don't comment on stuff I don't know anything about eg boat aero. Sorry.
@@JulianEdgar only a true scholar knows what not to say! If you want to explode your channel. Do a video titled aerodynamist reacts to teslas cybertruck, by the end of the week.
Thank you for the honest answer!
Please re-post at lower resolutions.
Wish you could make a video about aero bikes and the turbulence that new "aero socks" and aero kits cyclists are making clothing, I would love to add some silicone dots to a cycling kit to create the same effect without paying $500
Lipstick on a pig. A proper streamlined recumbent is *vastly* lower in drag than any traditional bike, with or without silicone dots.
@@JulianEdgar also easier to be crushed by a truck
Sure. But it's unbelievable how bad traditional bikes are in aero drag compared to what's actually available.
@@JulianEdgar they are acting within UCI limits for legal racing. No different then road legal additions to cars like side view mirrors windshield wiper that add drag but to be street legal they work with the rules. I was just curious if your background in drag forces could help us cyclists with new ideas to work with. Dimples on golf balls is the theory behind aero socks and aero clothing since the cyclist body is 70% of the drag
We have power meters and speed from GPS and wheel sensors, and I would love to experiment with different positions and clothes that help keep moving air around the body more "attached" as it flows over and around me
VG effect on such vehicule is weak on fuel saving effeciency
I’m just trying to blow water off my rear window
Yes, attached flow will achieve that.
@@JulianEdgar This is the solution I was looking for. I just got my first sedan after thirty years of hatchbacks (all of which had rear window wipers). If the sedan's rear window doesn't stay as clean as I'd like, even with water repellent to help rinse it off, I'll shop for vortex generators.
Those chicken finger ”vortex generators” are just total junk. Horrible shape for maximum drag and nothing else.
This video is a little unnerving, you give a lot of information, but don't actually come to a conclusion.
AirTabs marketing says they improve gas mileage, and handling on Semi's / RV's / etc.
The question I thought this video was trying to answer, do AirTabs improve gas mileage, and/or handling on sedans.
Have you answered that here?
The video covers what vortex generators can undoubtedly achieve. That is, they can cause flow attachment on surfaces where otherwise separation may have occurred. So, if handling instability or fuel mileage is being adversely impacted by premature flow separation, then they have the potential to improve these areas.