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The other day in the comments the topic of aerodynamic alterations came up. I mentioned that I have an airplane kit (full size, high performance) and that alterations that improve aerodynamics could be applied to cars. Before choosing my airplane kit I read about many different designs and their merits and histories. My airplane, the Velocity, is a "canard airplane" and has different requirements of its airfoils and therefore requires more testing. Early in its life a problem came to light. The main wing was slightly redesigned, with longer wings, designed so that the tips would stall at slower speeds. Existing kits were retrofitted with cuffs near the wingtips.

So this points out the first category of "fix": shape changing redesign or addons (like the Volt airdam). Another thing would be a belly pan. I have read somewhere a speculation that there is a belly pan on the Volt, but from what I could see it did not appear so.

A second fix is the addition of vortex generators. The placement and use of these are not really intuitive (to me at least). On any airfoil laminar flow is the smoothest, most efficient flow of air around a body. NASA and its predecessor, NACA, did a LOT of design in this area. It seems that for the typical wing that about the best that can be done is to get about 40% laminar flow. Now, and here is the counter intuitive part, when there is a transition from laminar flow to something else, the next best flow after laminar flow is "attached turbulent flow". This flow is controlled and moderately efficient. If you do nothing, or if you add a device to get turbulent flow after losing laminar flow then you get "detached turbulent flow" and this is bad because it is not controlled, not efficient. So what is a vortex generator? A small pair of vanes that may be an inch long and stick out from the attached surface 1/4 to 1/2 inch and the two vanes, usually made from one piece of plastic or sheet aluminum, are canted at a slight angle so they are not parallel, thus introducing the turbulence. Usually a row of these are attached across a surface.

A third device is "turblator tape". This really is the same as a vortex generator. An oversimplified description of this would be to take some plastic electrical tape and cut one edge with a pinking shears. The cross-hatched cut acts as many, many tiny vortex generators. The real stuff is kind of expensive however ($300 for one airplane if I recall properly). Because these micro VG's are so small, they need to be placed early enough in the airstream to get the vortexes formed early enough.

So, the counter intuitive thing is that triggering "good turbulence" at the right spot will actually reduce drag, and may give better handling.

If you Google (or Topeka :)) with various combinations of "vortex generator" "turbulence" "automotive" "drag" you should come up with some good info. When I was doing this the other day I found a guy's story about modifying cars and it had pictures of various cars that had good or bad features.

And yes the most famous and familiar example of controlled constructive turbulence is the golf ball. The dimples are like little VG's.
 

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Gee, what is the Reynolds number of the Volt compared to a golf ball, a radio control airplane, a piper cub, a Boeing 777?

Signed,

Too Lazy to Calculate it.


JohnK,
Your post took some effort. I thought someone
should say something, so I did.






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The other day in the comments the topic of aerodynamic alterations came up. I mentioned that I have an airplane kit (full size, high performance) and that alterations that improve aerodynamics could be applied to cars. Before choosing my airplane kit I read about many different designs and their merits and histories. My airplane, the Velocity, is a "canard airplane" and has different requirements of its airfoils and therefore requires more testing. Early in its life a problem came to light. The main wing was slightly redesigned, with longer wings, designed so that the tips would stall at slower speeds. Existing kits were retrofitted with cuffs near the wingtips.

So this points out the first category of "fix": shape changing redesign or addons (like the Volt airdam). Another thing would be a belly pan. I have read somewhere a speculation that there is a belly pan on the Volt, but from what I could see it did not appear so.

A second fix is the addition of vortex generators. The placement and use of these are not really intuitive (to me at least). On any airfoil laminar flow is the smoothest, most efficient flow of air around a body. NASA and its predecessor, NACA, did a LOT of design in this area. It seems that for the typical wing that about the best that can be done is to get about 40% laminar flow. Now, and here is the counter intuitive part, when there is a transition from laminar flow to something else, the next best flow after laminar flow is "attached turbulent flow". This flow is controlled and moderately efficient. If you do nothing, or if you add a device to get turbulent flow after losing laminar flow then you get "detached turbulent flow" and this is bad because it is not controlled, not efficient. So what is a vortex generator? A small pair of vanes that may be an inch long and stick out from the attached surface 1/4 to 1/2 inch and the two vanes, usually made from one piece of plastic or sheet aluminum, are canted at a slight angle so they are not parallel, thus introducing the turbulence. Usually a row of these are attached across a surface.

A third device is "turblator tape". This really is the same as a vortex generator. An oversimplified description of this would be to take some plastic electrical tape and cut one edge with a pinking shears. The cross-hatched cut acts as many, many tiny vortex generators. The real stuff is kind of expensive however ($300 for one airplane if I recall properly). Because these micro VG's are so small, they need to be placed early enough in the airstream to get the vortexes formed early enough.

So, the counter intuitive thing is that triggering "good turbulence" at the right spot will actually reduce drag, and may give better handling.

If you Google (or Topeka :)) with various combinations of "vortex generator" "turbulence" "automotive" "drag" you should come up with some good info. When I was doing this the other day I found a guy's story about modifying cars and it had pictures of various cars that had good or bad features.

And yes the most famous and familiar example of controlled constructive turbulence is the golf ball. The dimples are like little VG's.
what about a real generator usingthe wind i'am no enginer but a car moving at 50 mph should be like it being in a 50 mph wind
 

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A third device is "turblator tape". This really is the same as a vortex generator. An oversimplified description of this would be to take some plastic electrical tape and cut one edge with a pinking shears. The cross-hatched cut acts as many, many tiny vortex generators. The real stuff is kind of expensive however ($300 for one airplane if I recall properly). Because these micro VG's are so small, they need to be placed early enough in the airstream to get the vortexes formed early enough.


And yes the most famous and familiar example of controlled constructive turbulence is the golf ball. The dimples are like little VG's.
I have to say the Volt grill, like the background on this website that mimics the Volt grill, reminds me of Turbulators. Another way of reestablishing laminar airflow is slots that suck in air. Slightly like the edge of the grill. So there may be some sophisticated airflow design in the Volt.

I am no expert but Turbulators go on the leading edge and Vortex generators are placed where the wing/airframe taper inward.
 

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There is an image at murrayestevan.com
Compare that to the GM video Tunnel Vision

In the first image, she has googles and ear defenders and the separation occurs just past the anteanna (that isnt there). In the second - no googles, no ear defenders, but a clean airflow. Seems that the aerodynamics do fall down at speed and VG's should work. (I have some on order to try)
 

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Well, I gave it a try. I attached 14 VGs at the top of the rear hatch, on the black trim just behind the antenna. I knew from experience that I get a maximum oof 35miles at UK motorway speed (75+). That is now up to the 40 that I get at 55. The tufts that are tapped to the window, now remain pretty straight all the way down the window. Before, there was turbulance on the lower 6 inches over 50mph.

I am now going to get some Eagle claw ones to put on the underside of the bumper.
 

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Well, I gave it a try. I attached 14 VGs at the top of the rear hatch, on the black trim just behind the antenna. I knew from experience that I get a maximum oof 35miles at UK motorway speed (75+). That is now up to the 40 that I get at 55. The tufts that are tapped to the window, now remain pretty straight all the way down the window. Before, there was turbulance on the lower 6 inches over 50mph.

I am now going to get some Eagle claw ones to put on the underside of the bumper.
Could you post a picture of the positioning you used and/or a link to the VGs you used, if they are a commercial product? Your results sound impressive. My understanding is that VGs are sensitive to orientation, placement, spacing, and size, so getting some more details would be very helpful for others. I am interested in trying this. I am commuting at similar speeds daily and results like yours would make a real difference in reducing my gas miles driven.

I have already done some limited experimenting myself without making any progress. I was originally focusing on using VGs to eliminate the side window wind buffeting problem, but am also interested in efficiency, of course.

Was your reference to the bumper the front or rear one?
 

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It's called perpetual motion and defies the laws of physics... Even if 100% efficient, which is impossible, it would require the same amount of energy from the car to propel it forward that it would generate. There is no free ride...

what about a real generator usingthe wind i'am no enginer but a car moving at 50 mph should be like it being in a 50 mph wind
 

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Basically, any light aircraft supplier will have them. Aircraft kits are rather expensive, but you can usually email them and get a set for free. For installation, I went by the instructions here https://stolspeed.com/

Here is a picture of the roof while I was installing them. I got 14 of them in pairs (7 pairs) , The green paper is 10cm wide. The angle is 15 degrees.
Architecture Auto part Plant Vehicle


But here is the catch... below 55mph there is not going to be a visible improvement - that was as good as they could make it. So the improvement is only between 55 and 70. And then only between 5 - 10%.

I have a set of Air Tab style ones coming for the underside of the rear bumper. And no, it isnt "perpetual motion". I had an Opel GT that I used to drive from Blacksburg Va to Fairfax. This was through the Shenendoah mountains. I used to put it in neutral and coast down. At 85 it would just keep a contant speed ( in neutral going down hill). One day I was a bit faster and the flow was clearly laminar as it happily started accellerating.

Here is a link on how they work https://www.youtube.com/watch?v=eP-YUDe9HF0
 

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Thanks for the picture, that is very helpful. Do you think the air tab style would work at the top of the rear window? Yours appear quite a bit smaller than air tabs.

BTW, I think the comment about perpetual motion was in response to another post further up from 8 years ago that seemed to be (probably joking) about mounting a wind turbine on top of the car to generate electricity.
 

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The Air Tab style are rather big and ugly for my taste. Saying that, I have a set (8) of them for the underside of the rear bumper that I am going to attach when I get the chance. The green template was 10cm wide. 70mph is now fine and the problem (range crashing) has moved out to 75. you might want to push them closer towards the roof.
 
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