Who uses vortex generators?

[ChazInMT]

News flash....cars and airplanes operate in very different environments aerowise. Are they both moving through air....why yes, but that is where the similarity ends. Cars are in ground effect and have zero laminar flow going across their skins, so vortex generators would only serve to make a turbulent layer more turbulentier....which makes no sense, which is why they're crap when it comes to auto aerodynamics.



The "Vortex Generator" on the CRV Honda headlight assembly is an optical reflector designed to make the turn signal more visible from a greater angle on the opposite side of the car. I got em on my 04 Civic too.

[AeroModder]

I've used vortex generators on my Aspire with very positive results, but not quite as good as a kammback.

[ryannoe]

Originally Posted by ChazInMT

News flash....cars and airplanes operate in very different environments aerowise. Are they both moving through air....why yes, but that is where the similarity ends. Cars are in ground effect and have zero laminar flow going across their skins, so vortex generators would only serve to make a turbulent layer more turbulentier....which makes no sense, which is why they're crap when it comes to auto aerodynamics.



The "Vortex Generator" on the CRV Honda headlight assembly is an optical reflector designed to make the turn signal more visible from a greater angle on the opposite side of the car. I got em on my 04 Civic too.

News flash? LOL

Ground effect with respect to aircraft is a "phenomenon" where aircraft are able to increase pressure under their wings due to proximity to the ground. If we are talking car ground effect, it is the same "phenomenon" but reversed where a spoiler or the vehicle itself is angled downward increasing the low pressure under the body due to Bernoulli's principle of incompressible flow. It has nothing to do with vortex generator efficiency or practicality on vehicles.

Secondly, vortex generators re-energize boundary layers. Why would you think to energize a laminar boundary layer? Laminar skin friction is the least drag of any type and the least your worries. Never interrupt that flow with a vortex generator. Vortex generators are used to keep the turbulent boundary layer attached longer, thus reducing pressure drag and to give control surfaces authority.

I've used vortex generators on my Aspire with very positive results, but not quite as good as a kammback.

I plan to further investigate VGs on cars to reduce pressure drag.

AeroModder - Thanks for the prior testing, that was a good thread if I'm not mistaken, the same one you have your avatar picture of?

Wungun - I'm assuming the VGs are part of a STOL kit?

-Ryan

[RedDevil]

Originally Posted by ryannoe

... vortex generators re-energize boundary layers. Why would you think to energize a laminar boundary layer? Laminar skin friction is the least drag of any type and the least your worries. Never interrupt that flow with a vortex generator. Vortex generators are used to keep the turbulent boundary layer attached longer, thus reducing pressure drag and to give control surfaces authority ...

In some cases laminar flow does cause more drag than turbulent flow, especially so when it meets a surface that curls away in the wrong direction.
The Coanda effect will cause laminar flow to follow that surface, while turbulent flow will by and large move on in the same direction.

Most cars have curved edges on their rear bumpers. In a straight headwind the airflow along its sides will be turbulent, but when hit by sidewind it will be more or less laminar, curve round the bumper and create low pressure on the edge pulling it sideways and back.

I am planning to put zigzag tape on my 2011 Insight's rear bumper just ahead of the curve to break laminar flow. If that stops the jerking sensation when hit by sidewind then I will know that it works.

[ChazInMT]

Ryan,
I'm not talking about what happens when you're trying to land an airplane. And I don't mean shaping a car to increase down force. I'm talking about ground effect as opposed to free air, when your 10,000 feet up air acts differently than it does when you're 10 inches off the ground. Air does not behave the same around a bluff body when moving close to the ground. When looking at the aerodynamics of a car, you must remember that the air will move quite differently around the car when it is on the road as opposed to flying at 10,000 feet. So just like we don't design airplanes to fly at 2 feet off the ground, we don't design cars to fly at 10,00 feet. Get it?

So what I'm really trying to say is, because it works on airplanes, it doesn't mean it's going to work on a car.

Mitsubishi spent a crap load of time & effort dinking around with VG's with real engineers and real wind tunnels, they were able to gain 2%.....2%. Now how are you gonna top that? With good enthusiasm and a positive outlook?

Really, answer me this, besides the Mitsubishi EVO from a few years ago, what car manufacturer has put these on a production car? If VGs were able to reduce drag, you'd see them everywhere on everything. I suppose you could claim that "Big Oil" is keeping the car makers from getting too carried away with fuel efficiency. I suppose you also believe there are 100MPG carburetors out there too that they won't install.

Put this on your car, they claim it'll double you mileage.



Fact is, there's crap out there and there's things that really work, VGs fall into the crap realm.

Please post your positive results when you have them, you'd be the first to do so. ABA testing please, we all know that YMMV from hour to hour without any changes to the car. And long term tests have so many variables it isn't even funny.

I suggest you find yourself a nice hill to coast down at 40-50mph or so and see what kind of speed you maintain both with, and without, however many VG gimmicks you want to place on your car. Unless you're driving a crate, you will only see a tiny bit worse Cd when the VG's are in place. Certainly Wunguns Fiesta will suffer from any application of VG's.

Here's the Mitsubishi Thing

I didn't just fall off a turnip wagon Mr. Flight Test Engineer, I'd be behind vortex generators 100% if there was a shred of hope that they'd work on cars. There may be some cars out there with very poor aero design that VGs could help, but they're few and far between, most modern cars are fairly well optimized for what they are. VG tweeks will yield very small positive results at best and smallish negative ones at worst.

Waste your time if you want. Real gains can be made by blocking your grill, pumping up your tires, and lowering your front airdam among other things. Unless you want to radically reshape your car, you're stuck with what you got, VG's just won't do much.

[RedDevil]

... My bad, I just realized this thread is about deliberately generating vortices instead of just turbulence.
I see no way how vortices could help reduce drag, I'm no expert though.

[ryannoe]

Chaz - Something irritates me about the way you present your thoughts. I'm going to try and bandaid as much of your rash as I can.

Car designers have a lot of missions to fill, regulations to abide by, etc. Why do you think commercial jets have winglets? Do you think winglets are more efficient than just extending the wing longer? It isn't. They are doing this to get the maximum efficiency while staying inside regulation. It would really help aero to cut down on the fuselage but that's part of the aircraft's mission so it can't be changed. All of the low hanging fruit has already been picked.

Also, there isn't much that separates someone sitting in the corporate office designing up the next car and you and I. Once they get what they think is good, I'm sure they sit through a design review and human factors engineers tweek it to less efficiencies to provide "better" curves. I'm sure you know this: they want to provide bad ass engineering, but that doesn't put food on their plate. They need to sell cars.

If the Prius and Insight gets 51 mpg and 51 mpg is better than 28 mpg, why isn't every single car on the road a Prius or Insight? Because the rest of the world doesn't care. They're happy with their sexy Z4's (love the way those look), A5's, or maybe an older Civic. Fact is, looks sold that car, and I'm 99.99% sure they didn't have the Cd posted on the sticker. "Honey, look at this one, it has a flat plate drag of only 0.7!" said NO ONE EVER.


RedDevil - unless you have introduced a new surface, I have my doubts that it is laminar at your rear bumper. Laminar flow is more likely to separate from the vehicle than turbulent flow (which I suspect is what you have). I'd like to hear what happens. Don't forget to post it for us!

-Ryan

[niky]

Originally Posted by ChazInMT

News flash....cars and airplanes operate in very different environments aerowise. Are they both moving through air....why yes, but that is where the similarity ends. Cars are in ground effect and have zero laminar flow going across their skins, so vortex generators would only serve to make a turbulent layer more turbulentier....which makes no sense, which is why they're crap when it comes to auto aerodynamics.



The "Vortex Generator" on the CRV Honda headlight assembly is an optical reflector designed to make the turn signal more visible from a greater angle on the opposite side of the car. I got em on my 04 Civic too.

They do dual purpose. If the only purpose was visibility, they could put it anywhere. Honda did it exactly on the corner, as Toyota did with the older Camry lights, specifically to deflect airflow from the the side mirrors.

Apparently, Honda felt that "visibility" was unnecessary on the new CR-V... but then, the side mirror seems more aerodynamic, now, so the hard edge on the corner of the vehicle is no longer necessary.

[CigaR007]

I believe VGs should be used in conjunction with other drag-reducing methods in order to be fully effective. They have to be implemented correctly though and that is where the challenge resides. Experiments based on sound studies such as Mitsubishi's are worth undertaking, IMO. I know I will, eventually.

[caferacer51]

I was under the impression that the VG on the rear roofline of the Lancer was to aid rear down force? Surely that goes against this conversation of VG use for economy?

And in the game of fuel economy, is 2% not a substancial gain?