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

[Vekke]

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.

----

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")

[aerohead]

Originally Posted by Vekke

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.

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

[CigaR007]

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

[LoDrag]

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.

[Cd]

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.

[MetroMPG]

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

[Cd]

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 ! )

[MetroMPG]

Originally Posted by Cd

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 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.

[Piwoslaw]

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

[Vekke]

Originally Posted by MetroMPG

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.

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