Interesting Aerodynamic Cars (Mike Vetter's ETV, also Avion)

[gafhj]

Originally Posted by aerohead

I agree with all the members who've already mentioned laminar boundary layer bodies.
The Delft team told me that this was the premise for their designs.
Keeping the max cross-section aft held the forebody in a favorable pressure gradient for laminar boundary layer (low skin friction),The turbulent boundary layer transition was held far back on the body,and so much kinetic energy was available in the TBL due to the forebody,that more aggressive curvature in the rear (reduced wetted area ) could maintain attached flow.
This is all predicated upon 'calm' conditions.Once the wind comes up,the body in immersed within Earth's turbulent boundary layer,and the ambient air turbulence kills the laminar boundary layer,especially in a crosswind which contaminates it,forcing an immediate TBL transition.
Keeping the envelope as small as possible (length) helps because it directly affects Reynolds number,of which LBL is directly related.

That's interesting. I used to think that Eivie was the best design out there, just limited by the riders (there were 2, Damjan Zabovnik, but also Francesco Russo had a bike like that built together with Damjan). Much closer to tear drop than Eta of VeloX as well as lower frontal area. There's a wheel far in the front which is not good though.

Still, I've seen people explaining its uniqueness by being too extreme for most riders. Sounded reasonable enough, I hadn't questioned it.

But according to what you report, the design may simply be inferior in low wind (which is probably the only state that matters when setting records).

Could you tell more about the Delft comments? Can you share your thoughts too?

Added:
On a related, but separate topic, have they talked about their gripes with CdA measurements in their wind tunnel?
I ask because on their blog they say:

Even though the values have dropped greatly in comparison to last wind tunnel test, we still have our doubts about them because we noticed a lot of fluctuation in the measurements. Therefore, the wind tunnel measurements do not seem to be very accurate.

I ask mainly because the current record holder for the lowest ground vehicle Cd is Ecorunner V from another Delft team. The said fluctuations make me have my reservations about whether Ecorunner V really has drag so low.

[kach22i]

[VIDEO] "THE ECORUNNER V GETS ONE IN 5000 '
May 14, 2015
[Video] 'De Ecorunner V haalt 1 op 5000' | Hartvoorautos.nl

Two categories
at the Shell Eco-marathon to do more than 500 teams from 50 countries and all those engaged in building the ultimate energy-efficient vehicle. The two categories from which the teams can choose their Prototype and Urban Concept . In the first category we see a lot of futuristic vehicles to such an energy-efficient vehicle and the second category we see vehicles that may also be acceptable for use on public roads.

7 Types of fuel
The teams must choose from seven types of fuel. These are; gasoline, diesel, ethanol, GTL, CNG, hydrogen and battery-electric. The Shell Eco-marathon so is not about speed but about efficiency.

Translated by Google Chrome.


Six students dropped out of school for a year to be part of one team project and work on it full time.

3:50 mark shows the road/racetrack scramble of different designs................so cool.

Nine student teams from Poland in Shell Eco-Marathon 2013
http://scienceinpoland.pap.pl/en/new...thon-2013.html



The eco-friendly wacky races: 200 teams from across Europe compete to create most energy efficiency car on the road
http://www.dailymail.co.uk/news/arti...-car-road.html


http://thegeec.ie/sem2015/happens-now/

[freebeard]

Back to cars. Yay.



Why can't today's freeways look more like that?

[Frank Lee]

Originally Posted by freebeard

Why can't today's freeways look more like that?

Because fuel isn't expensive enough... yet.

[gafhj]

And stylists worry that all cars would look the same...

[kach22i]

https://www.behance.net/gallery/1561...l-Eco-Marathon




http://www.soufflerie2a.com/en

[sgtlethargic]

http://i.kinja-img.com/gawker-media/...5847885127.jpg

Maybe I'll resize it or something, later.

[aerohead]

Originally Posted by gafhj

That's interesting. I used to think that Eivie was the best design out there, just limited by the riders (there were 2, Damjan Zabovnik, but also Francesco Russo had a bike like that built together with Damjan). Much closer to tear drop than Eta of VeloX as well as lower frontal area. There's a wheel far in the front which is not good though.

Still, I've seen people explaining its uniqueness by being too extreme for most riders. Sounded reasonable enough, I hadn't questioned it.

But according to what you report, the design may simply be inferior in low wind (which is probably the only state that matters when setting records).

Could you tell more about the Delft comments? Can you share your thoughts too?

Added:
On a related, but separate topic, have they talked about their gripes with CdA measurements in their wind tunnel?
I ask because on their blog they say:

I ask mainly because the current record holder for the lowest ground vehicle Cd is Ecorunner V from another Delft team. The said fluctuations make me have my reservations about whether Ecorunner V really has drag so low.

*Hucho (PhD Mechanical Engineering,he ran VW's climatic wind tunnel for 10-years,he wrote the book on aerodynamic optimization) says that the theoretical drag minimum for an automotive body,with 'normal' ground clearance,respecting SAE clearance issues would be on the order of 0.08 with perfect wheel integration.This presumes an entirely turbulent boundary layer above around 20-mph.
*The Delft team is flirting with 'laminar' bodies which presume low Reynolds numbers which can only occur with small,short bodies of rearward-biased maximum cross-sections ( 1st minimum pressure),and completely calm conditions (like flight values for a wing or fuselage many thousands of feet above the ground,above the 'weather').
*If the Delft body is in 'traffic',or if there is any crosswind,it will experience crosswind contamination which immediately forces a transition to a turbulent boundary layer ahead of it's 1st minimum pressure location; or if in ground wind,it will be submerged in Earth's turbulent boundary layer,which forces the LBL to TBL trasition.
*The ultra-low-drag of the LBL body defaults to a TBL drag coefficient based upon it's local Reynolds number.
*Delft's Cd 0.055 might become Cd 0.08 at Battle Mountain,as I believe that a' legal wind' is up to 8-mph,and usually a crosswind during IHPV Speed Trials.
*Their bodies are widest far back,helping to keep the front in a positive pressure regime

*If they're blown off the track and scratched up,as in 2014,they have to refinish the damaged area,since as little as a bug splatter can render the LBL impotent


*A TBL racebike would just continue racing with all the cosmetic damage,unaffected.

[freebeard]

Originally Posted by aerohead

*Their bodies are widest far back,helping to keep the front in a positive pressure regime

http://justacarguy.blogspot.com/2016/04/bugatti-type-51-dubos-coupe-1931.html

[Hypermiler1995]

Turkish Electric Car Goes 436 KM On Sincle Charge | Green Prophet