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Something that I was unaware of since most of the photos don't really show this... the roof of the 2016 Volt has this indentation with curved ridges. I took this picture last weekend at the O.C. International Auto Show, where Chevy had two 2016 Volts. A black one and a white one.

 

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Seems useless to me. Adds a little drag and doesn't help the look. I'm shocked more cars aren't shaped like teardrops. All the car magazines in the 80s and 90s had pictures of future concept cars looking like that. But instead we get ugly for EVs, like the i3, front end of the tesla model X, front end of the volt, the fiisker, the leaf. Why can't they make an electric car drop dead gorgeous? Oh yeah, they did, that's the ELR.
 

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No, it's not an NACA duct, since there is no inlet.

It could be for reinforcement/strength.
This design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices which deflect the boundary layer away from the inlet and draws in the faster moving air, while avoiding the form drag and flow separation that can occur with protruding scoop designs.
Think of the ass-end of the car, where the drag happens as the inlet. Inlet or not, the concept of the shape is the same.

As I understand it from GM propaganda, the tail lights are designed to reduce drag too. I expect they also produce some "counter-rotating vortices".
 

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"The sculpted lines are inspired by sands blowing through the wind."
 

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I agree with Mr. Dave its probably a form of vortex generator.
 

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In addition to air flow, the ridges also strengthen the roof more than a smooth roof. Same with the hood.
 

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another thing that came to me is that if the roof height isn't needed in the center for egonomics for our heads. Then lowering the roof height in the center effectively reduces the frontal cross section pushing less car through the wind.
 

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anybody drive thru a rain storm yet.how dirty is the back of the car getting?
 

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another thing that came to me is that if the roof height isn't needed in the center for egonomics for our heads. Then lowering the roof height in the center effectively reduces the frontal cross section pushing less car through the wind.
Then why not lower the entire roofline and get an even lower cross section? Though I'd like to see a voltec with a raised roofline
In the form of a wagon. My 5'11" daughter hates the rear seat of the g1 as her head has to be positioned behind the head liner just underneath the glass.
 

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The last 1/2 mile of road to our house is unpaved, and rear-end dust is a real problem, especially under the deck lid. The California Duster is somewhat helpful, but if our V was a dark color, it would be impossible to keep it looking spiffy!

BTW, while a teardrop shape is ideal from a fluid dynamics perspective, the work of Dr. Wunibald Kamm is the basis for most modern aerodynamic automobile designs. From Wikipedia:
While the realities of fluid dynamics dictate that a teardrop shape is the ideal aerodynamic form, Kamm found that by cutting off / flattening the streamlined end of the tear at an intermediate point, and bringing that edge down towards the ground, he could gain most of the benefit of the teardrop shape without incurring such a large material, structural, and size problem. The airflow, once given the suggestion of the beginning of a turbulence-eliminating streamlined teardrop tail, tended to flow in an approximation of that manner regardless of the fact that the entire tail was not there. This is called the Kamm effect.
 

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The last 1/2 mile of road to our house is unpaved, and rear-end dust is a real problem, especially under the deck lid. The California Duster is somewhat helpful, but if our V was a dark color, it would be impossible to keep it looking spiffy!

BTW, while a teardrop shape is ideal from a fluid dynamics perspective, the work of Dr. Wunibald Kamm is the basis for most modern aerodynamic automobile designs. From Wikipedia:
Thanks for the reference. That still doesn't explain why there aren't any cars that look like the fron of a teardrop with the tail chopped off.

A modern version of this could look quite striking

http://www.spiritoftomorrow.com/uploads/1/6/2/2/1622945/9765292.jpg?557x374
 

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Yes I believe this a form of the pagoda roof design. The Scion FR-S has something similar.



It provides some benefits to airflow, while adding strength as Raymond mentions.
 

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That's for the reference. That still doesn't explain why there aren't any cars that look like the front of a teardrop with the tail chopped off.

A modern version of this could look quite striking
This one came pretty close, and it is indeed, "quite striking"

shelby daytona cobra.jpg
 

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Don't forget Buckmeister "Bucky Balls" Fuller's Dymaxion

dymaxion_detail01.jpg dymaxion.jpg
 
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