Vortex generators

[aerohead]

Originally Posted by fbov

Real science behind them...
Aerodynamics Research Revolutionizes Truck Design

Like any aeromod, you need a special case to see a big effect. Eddie's video shows a special case. Incremental beneficial aero effects are small, with large downsides when done poorly. On most modern cars, the latter generally dominates as factories have wind tunnels and real engineers; if VGs were aero-salvation, they'd be on the cars now.

Have fun,
Frank

Somewhere in my reading,it was mentioned that automakers considered VGs.They'd have to be stamped into the sheetmetal for mass production,they'd be a challenge in a carwash,and in a pedestrian impact,if the person somehow made it over the roof,VGs would ad injury to injury.

[cyclopathic]

Found this article:
Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars (PDF Download Available)

RESULTS AND DISCUSSION

A total of 26 combinations are tested for the car model by changing the flow angles (= 0and 30), spoiler angles (=0and 45) andorientations of vortex genartors (co-rotating and
4counter-rotating) in order to find out the optimum conditions for which drag coefficient is minimum. The following conclusions can be drawn based on this experiemntal studies.Referring to Fig. 7, a marked improvement in static pressure along the car roof, especially at the car rear that is noticed at a flow angle () = 30by subsequent use of rear spoiler (at = +45) and co-rotating vortex generators. Here,the suction reduces to an extent and become very close to zero static pressure values near the rear end of the car. This incident clearly indicates that the flow separation zone gets reduced with the use of spoiler along with VG. It is also observed in Fig. 7(a to c) that a positive pressure builds up on a little portion of the car roof close to the windward side

There is more in article, but it is clear that at least in combination with rear spoilers VGs help to reduce aerodrag.

[aerohead]

Originally Posted by cyclopathic

Found this article:
Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars (PDF Download Available)

There is more in article, but it is clear that at least in combination with rear spoilers VGs help to reduce aerodrag.

It is only clear in the context of the specific vehicle investigated (Mitsubishi Lancer?)
Since VGs were intended for notchback type cars,the caveat to VGs would be,if you have a notchback car very much like the Lancer,then there is an opportunity to see a very small drag reduction with the addition of properly-sized and positioned VGs.
No broad and sweeping claims can be made to the otherwise.

[2000mc]

Originally Posted by aerohead

No broad and sweeping claims can be made to the otherwise.

.....if you get to try no less than 26 combinations with unlimited wind tunnel time? Given that, you could probably find a configuration of gluing bricks on that helped. I'd be more curious what their results were in their 1st attempted configuration

Edit: ok, is the +45 spoiler a lift and drag inducing worst case scenario no one would ever use ever? Or am I seeing it wrong

[cyclopathic]

Originally Posted by aerohead

It is only clear in the context of the specific vehicle investigated (Mitsubishi Lancer?)
Since VGs were intended for notchback type cars,the caveat to VGs would be,if you have a notchback car very much like the Lancer,then there is an opportunity to see a very small drag reduction with the addition of properly-sized and positioned VGs.
No broad and sweeping claims can be made to the otherwise.

I agree with you that VGs are not a magic item which gives you higher MPG by just having them, and use of them should be looked in context. What I specifically refer to is that VGs when used properly can help to increase efficiency of properly designed spoilers by increasing speed of flow and decreasing spoiler stall speed.

If not used properly they will do nothing or hurt, but this can be said of any aero mod.

Edit: not sure which vehicle they used. There are more production cars/SUVs use them now. I followed hybrid Avalon last night it had OEM VGs on rear underpan.

[cyclopathic]

Originally Posted by 2000mc

.....if you get to try no less than 26 combinations with unlimited wind tunnel time? Given that, you could probably find a configuration of gluing bricks on that helped. I'd be more curious what their results were in their 1st attempted configuration

Edit: ok, is the +45 spoiler a lift and drag inducing worst case scenario no one would ever use ever? Or am I seeing it wrong

My biggest issue is that we don't even know what is the car configuration. Sedan? Hatchback? How aero iit was before they started? So there is not enough information to be useful in designing aero efficient vehicle.

What is encouraging that study confirms that properly positioned VG and spoiler combination works better than spoiler alone, and VGs when used properly can improve aero efficiency.

[ConnClark]

As someone who has looked into this in depth, vortex generators can work on a car. Want proof? Mitsubishi actually did implement them on their Evo Lancer and got a 2 to 4% reduction in drag. The problem is they needed to do a full CFD simulation and a wind tunnel to verify it.

With my old 300SD I did some CFD simulations and was able to get about a 3% reduction in drag. Would it have saved me any fuel? not really because my most of my driving was in town and short trips.

What I learned from the simulations.

1) Sizing the VGs was very important. If they were too big they just created drag. In other words don't expect VGs designed for semis to work for your car(they might but it won't be optimal).

2) Proper placement is very important.

3) To get VGs to work where you want them to you might need to address problems further up stream.

4) the number of combinations is infinite so you will never find an optimal solution.

5) Unless your car's aerodynamics is absolutely abhorrent don't expect to get more than a 5% improvement

[Vman455]

Found this on Toyota's website: "Turbulent air increases drag, which adds wind noise and reduces efficiency. Camry features small, specially placed design features called vortex generators to help smooth things out. Not only do these help Camry maximize its efficiency, they help keep things quiet inside the cabin too."

I think this refers to the small VGs manufacturers today use on exterior mirrors and taillight and headlight lenses (my Prius has a single VG on each headlight, molded into the clear plastic), but they are VGs nonetheless, and if they didn't do something the manufacturers wouldn't go to the trouble of using them. That said, they are very small in size and number. Slapping VGs on the back of a car willy-nilly is an exercise in futility.

I'm remembering just now, too, the wing on the back of the SRT-10. It had a trough on the underside, about an inch long, that ran the width of the wing.



Hard to see in this picture (not my truck), but it's there. I seem to remember Dodge claimed the trough gave a slight improvement in aerodynamic efficiency versus a spoiler with no trough. With the standard tonneau cover in 2006, however, the wing was redesigned and the trough was gone.

[cyclopathic]

I am not sure starting when but hycam and hy Avalon have little tabs under rear bumper. Prius C has 2 tabs on tail lights and one on mirror.

[aerohead]

Originally Posted by cyclopathic

I agree with you that VGs are not a magic item which gives you higher MPG by just having them, and use of them should be looked in context. What I specifically refer to is that VGs when used properly can help to increase efficiency of properly designed spoilers by increasing speed of flow and decreasing spoiler stall speed.

If not used properly they will do nothing or hurt, but this can be said of any aero mod.

Edit: not sure which vehicle they used. There are more production cars/SUVs use them now. I followed hybrid Avalon last night it had OEM VGs on rear underpan.

I think it's time for images.
Are we talking 'wings' or 'spoilers'?
If VGs allow the inviscid flow to more closely follow the aft-body contour of a car,it won't really alter the local air velocity.
A wing will already be above the separated flow in 'clean' air and little affected by VG modification.
If a spoiler is in separated flow,VGs can help with reattachment onto the boot/spoiler,a clear advantage.
A spoiler doesn't have a stall speed.It's just a reattachment apparatus on a car with designed-in separation.
And with a wing,the VGs would have to be on the wing itself to be able to alter its stall characteristics,something well researched since 1920.
The other thing,is that there are about six different types of VGs in use.Each has a specific advantage.All six types would want to be investigated.And their performance depends on the local boundary layer thickness,along with orientation,location,and spacing.
They require a wind tunnel for investigation.If you're going to do a moving-floor tunnel as is available in North Carolina,you're looking at $4,000/hour for testing.And you'll be there for days.
I agree that VGs have their place,but we may be forced to leave it up the the Mitsubishi's of the world to figure out how to best use them.