Vortex Generators for a Car????

Old Geek

Old Geek

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I was at the Subaru dealership this morning. You can buy vortex generators for your WRX. I couldn't find a salesperson to ask whether they would cause your stall to break more gently and not turn into a spin...
 
Wait...you were at a car dealership and COULDN'T find a salesperson???

Were they open?
 
Are you talking about a diffuser? If so them dumb looking things actually do create some significant down force. Flat bill hat is optional hahaha
 
Bunch of the little "Fast and Furious" racers use VGs. Not just a Subaru thing.
 
Fearless Tower said:
Any idea why? Don't VGs typically generate more lift which is typically bad for ground vehicle handling?
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The theory is they cause air to flow down the rear of the car and create more down force. It's what every FWD import needs :rofl:
 
Sure. I've seen them on the rear spoilers....
 
Fearless Tower said:
Any idea why? Don't VGs typically generate more lift which is typically bad for ground vehicle handling?
Click to expand...

In the case of vehicles, it's similar to dimples on a golf ball. They delay boundary layer seperation thereby reducing wake drag. Increase speed and gas mileage. Secondary benefit is down force on a spoiler as well.

Whether or not it's worth investing for a typical auto. :dunno: I've actually thought about buying them in the past just as a test bed. Really don't care for the looks of tiny fins on the top of my vehicle though.
 
Fearless Tower said:
Any idea why? Don't VGs typically generate more lift which is typically bad for ground vehicle handling?
Click to expand...

The trick to car airflow is to reduce the vortex off the back, that is your greatest useless drag. VGs have a limited ability to help modify the airflow, especially when you start needing wings for down force. The amount of lift that a VG can provide is far outperformed by downforce appliances, so no significant loss of useful drag. You can use VGs to create boundary layers to help direct the airflow to use it to greatest effect and minimize drag. You can also use them manage how the cowl vortex forms to help "squash" the HP zone in front of the windshield by dragging it forward which can help your windshield drag as well.
 
MotoFlier said:
The theory is they cause air to flow down the rear of the car and create more down force. It's what every FWD import needs :rofl:
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The Subaru is actually a AWD car and the WRX, especially the STI, is quite the car.

Only VGs I've seen were on the MR Evo (also a AWD turbo car)

112_0512_wrx_evo_13z-2006_mitsubishi_lancer_evo_ix_mr-vortex_generators_view.jpg
 
If it actually did anything to reduce drag and increase speed, or mileage, they would be standard on every Prius, or Chevy Volt. If they actually did anything to improve the cornering of a car, you would see them on Porsches, Corvettes, BMWs, etc. We see them because they are ridiculous car fashion. Just like red brake calipers, those stupid little hoops they put on the back of Civics, or the ubiquitous wing.
 
James331 said:
The Subaru is actually a AWD car and the WRX, especially the STI, is quite the car.

Only VGs I've seen were on the MR Evo (also a AWD turbo car)

112_0512_wrx_evo_13z-2006_mitsubishi_lancer_evo_ix_mr-vortex_generators_view.jpg
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I know I was just playing off the fast and furious comment hahaha.
I don't know how well the VG's work but the Diffusers that mount under the bumper actually make a huge difference.
 
Dav8or said:
If it actually did anything to reduce drag and increase speed, or mileage, they would be standard on every Prius, or Chevy Volt. If they actually did anything to improve the cornering of a car, you would see them on Porsches, Corvettes, BMWs, etc. We see them because they are ridiculous car fashion. Just like red brake calipers, those stupid little hoops they put on the back of Civics, or the ubiquitous wing.
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http://www.formula1-dictionary.net/canards.html

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Dav8or said:
If it actually did anything to reduce drag and increase speed, or mileage, they would be standard on every Prius, or Chevy Volt.
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Maybe. Or maybe someone figured those priuses are ugly enough without them. Afterall, they work on wings, but not every plane has them.
 
Dav8or said:
If it actually did anything to reduce drag and increase speed, or mileage, they would be standard on every Prius, or Chevy Volt. If they actually did anything to improve the cornering of a car, you would see them on Porsches, Corvettes, BMWs, etc. We see them because they are ridiculous car fashion. Just like red brake calipers, those stupid little hoops they put on the back of Civics, or the ubiquitous wing.
Click to expand...

You cannot assume that at all. Besides which, if you don't mind an ugly car, you can design out the usefulness. But overall, at road speed the effects are minimal enough it's not worth the production cost. If you want to improve your Prius, you'd put a simple flange on the back.
 
Downforce is lift in the other direction. Vortex generators can make a difference even at low speed as they help airflow remain attached just like on planes. It can allow more downforce by reducing lift or by allowing airflow over areas that would normally be in turbulence. We used VGs on indycar wings at very low speed tracks like Long Beach and Vancouver BC. They increased the downforce measurably at speeds as low as 30mph. It allowed the speed through some of the very tight corners to increase while maintaining control of the car. It doesn't always take a thousand pounds of downforce to decrease lap times substantially and drag isn't always the point of racing accessories. If you have the power to overcome the drag than a few extra pounds of downforce is worth the drag. Unlike planes which have a loss of horsepower connection to propulsion due to propeller slip you will find that cars are more positively connected to the means of moving. Adding downforce not only allows more speed through the corners due to better "stick", it also increases the stick of the driving tires so better horsepower to the ground. An indy car in speedway trim....small wings and underbody, travels faster than a Bonanza with lap speeds at indianapolis of 240mph plus. This includes the 4 turns where speed drops to around 228mph. The cars at that time had a little over 800 hp which is around 3 times what some Bo's have. All that extra power went into overcoming drag caused by the downforce producing wings and underbody. Its an alien environment and tough to understand from a flying point of view. Sure the wings create lift just like ours but in the other direction and they care less about drag than we do because it doesn't affect them like it does us. . . .

Frank
 
Years ago a race car aerodynamicist named Gary Wheeler marketed a blow molded strip of VGs that looked like inverted NACA ducts. His idea at the time was to use them at the front of trailers, kind of like the little lip spoilers that you sometimes see. Their effect was to keep the boundary layer attached to the trailer side rather than letting it separate and create a lot of drag. At the time I had a race car trailer that was a real bitc# to tow. I added the vgs along the sides and at the top. They gave a huge reduction in drag, shown as MPG. It was interesting in fact, when I was towing in heavy crosswinds I could feel a burst of drag when a gust outcompeted the vgs and separated the boundary layer.

Aerotab acknowledges Wheeler here: http://www.airtab.com/hall-of-fame.htm His patent is here: http://www.google.com/patents/US5058837 I hope he is still alive and making some money on it. He's a great guy.

Re VGs on cars I can see that they would be undesirable because they stick up and can be easily damaged. I can see that they would be desirable "cool factor" additions like the ridiculous little wings and luggage handles that seem to be de rigeur on front-drive grocery getters. I cannot see that they would make enough aerodynamic difference to matter.

Henning is right to identify the rear of the car as the main drag source. First order, the drag is proportional to the cross-sectional area of the vehicle at the point where the flow separates. This is why you see subtle tapering of cars towards the rear and why all glass is now flush. Unseparated flow will follow a taper angle up into the 10-15 degree range (more or less the same as our airplanes' stalling AOA). Second-order things can help, like lip spoilers and the "thin base shell" hollowing you see at the rear of rifle bullets. Strictly speaking, though, it is not the vortices that cause the drag. The vortices are created as a consequence of the air sort of tearing off the back of the low-pressure "bubble." Interestingly, vortex shedding is proportional to velocity. There are flow meters that use this principle by putting a bluff body into a pipe and then using a pressure sensor to sense the vortex shedding frequency.

Anyone really interested in this would enjoy "Fluid Dynamic Drag" by S. F. Hoerner (http://www.amazon.com/Fluid-Dynamic-Drag-Hoerner/dp/9993623938). Hoerner was a Luftwaffe aerodynamicist. Unfortunately the book is now a collector item and quite pricey.
 
Anyone care to explain how vortex generators would make this more efficient?
 

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