Drag reduction modifications in wind tunnel: Audi A2 from Cd 0.288 to 0.204
 

Hi,

Thanks to Ausias who tipped me off with this Cd study:

http://wwwm.coventry.ac.uk/researchn...%20Vehicle.pdf

Lupos 0.25 Cd target starts to feel pretty plausible without chopping the roof ;).

Enjoy.

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SUMMARY...

(added by MetroMPG, because these online files have a bad habit of disappearing...)

• START: MIRA wind tunnel showed a stock co-efficient of Drag (CD) of 0.288
• COOLING: vents, intakes, panel gaps taped on front end - Total Contribution: 9% of total Drag
• Underfloor:-Foamboard and tape -All components covered -Total Contribution: 7% of total Drag
• MIRRORS - door mirrors removed: -Total Contribution: 5% of total Drag
• Wheels and Wheel arches: Wheel Spoilers / spats; smooth wheel covers; Wheel Arch Blanking (rear fender skirts); Underfloor Wheel Arch Blanking
• Base pressure recovery (tailgate "box cavity")

http://ecomodder.com/forum/attachmen...1&d=1332944398

0.25
 

Cd 0.25 should be a walk in the park.I'm certain of it.Even lower if you like.:)

Awesome paper. Makes it easier to quantify every mod accordingly.

Good simple paper to guide mods. I'm a wind tunnel engineer at work and like seeing studies like this with measured data.

Thanks for sharing. :D

I had seen mention of the " box cavity" method of reducing drag at the rear in an old paper* from the UCDavis " future car " hybrid Ford Taurus .
It's good to see results quantified here .

* no longer online.

Vekke - nice find! I added the summary to post #1, since these files often disappear from the web after a while.

If you notice the caption on the bottom of the picture of the A2 at the top of the paper, there is mention of the A2 being introduced at .25 Cd .
This number is often given as the official Cd in published literature ( I've also seen .27 )
This makes me wonder what would have caused such a drastic rise in drag to .288 .

The only visible changes are the style of wheels, and surely this would only account for a count or two .

( And it also makes me wonder if they did the same mods to the .25 version, just how low of a Cd they would have achieved ! )

The A2 was available in several different trim levels/models , one of which was a high-efficiency version ("3 L" diesel). That's what the .25 figure refers to. It had a different grille, wheels, tires (size) and partial underbody panels (if memory serves), and possibly also a lower ride height.

Ride height is one mod our experimenters didn't attempt here.

Too bad those slides didn't give more info about the effects of the rear box cavity versions.

A2 3l Had 0.25
145/80R14 tires
Lower ground clearance
smooth hubcaps
almost fully blocked front grille
smooth underside to some extent
plus lots of small modifications

Lupo 3L has smaller mirrors I am not sure if A2 has them on also