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

[ausias]

Originally Posted by Vekke

Hi,

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

Our Research | Coventry University

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")

Being quoted by the Finnish Master of the Universe Ecomodder.


It is amazing the power of the duct tape.

[UltArc]

Originally Posted by fusion210

I found this, but it seems like it's more of an overview of the study in the first post? I haven't seen the original.

http://www2.warwick.ac.uk/fac/sci/wm...view_may11.pdf



I'm sure they're stored somewhere. If someone wrote them a nicely worded email I'm sure they'd send you the files.

Thank you.

Maybe, I'll have to look for an e-mail address.

[ausias]

This link is working:
Information: How To Reduce Drag From 0.28 to 0.20 (Scholastic more than anything)

Direct donwload from the Audi A2 forum is: http://www.a2oc.net/forum/attachment...9&d=1360233797

To read online in Scribd
Session 4 - 1 - Hussain Ali - Drag Reduction on a Production Vehicle

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[aerohead]

Originally Posted by CigaR007

I have often wondered if there is a "synergy" effect when combining different drag reduction mods. Would there be a perfect combination ?

Hucho tells us that for the lowest drag we'll need airfoil or half-body shapes.
*The 2005 NUON NUNA,@ Cd 0.07 would be the 'airfoil' benchmark.
*The 2013 Cambridge University CUER would be an okay 1/2-body benchmark,@ Cd 0.10.
Mods which push a body in those directions would be winners.
The key is the high sectional density and elongation which allow streamlines to converge without separation,leading to a higher base pressure.

[aerohead]

I did a photo-enlargement of the graph,measured each 'bar',then did linear interpolation to develop Cds for each 'bar.' With Cds attached to each mod,it's easier to evaluate their individual contribution.
Reading from left-to-right:
*0.2881
*0.2818
*0.2656
*0.2383
*0.2353
*0.225
*0.2214
*0.2162
*0.2143
*0.2100
*0.2044

[Vman455]

Last night I came across a paper in Sustainable Vehicle Technologies: Driving the Green Agenda (2012) by a Tata Motors engineer involved in this study. In addition to much more information on the project, they also took the car to the Soufflerie 2A aeroacoustic tunnel in Paris to test the various configurations with a moving ground. Here's what they report:

[freebeard]

Interesting. Any idea of what 'suction upstream of the belt' means? Aren't the belt and the air moving at the same speed?

[California98Civic]

Originally Posted by freebeard

Interesting. Any idea of what 'suction upstream of the belt' means? Aren't the belt and the air moving at the same speed?

I would bet that the belt doesn't encompass the entire floor inside the wind tunnel. So that would mean there must be an area ahead of the car and head of the belt but in the windstream where the air is passing over the stationary floor. The point at which the air flow encounters the belt would be interesting in terms of turbulence, wouldn't it?

[Vman455]

Originally Posted by freebeard

Interesting. Any idea of what 'suction upstream of the belt' means? Aren't the belt and the air moving at the same speed?

Above the fixed floor in front of the car, a boundary layer builds up; the suction slot dissipates that boundary layer so it doesn't skew the results over the moving belt.

[aerohead]

Originally Posted by freebeard

Interesting. Any idea of what 'suction upstream of the belt' means? Aren't the belt and the air moving at the same speed?

On the highway,the road is stationary and it doesn't have any boundary layer,just the car's body.In the wind tunnel,the moving belt may be at a different velocity as the airstream,creating a boundary layer which must be vacuumed off,so as not to create a condition a car wouldn't see in the real world.In some stationary-floor tunnels,they just lift the car up enough to clear the thickness of the boundary layer which forms.The uprights at DARKO, elevated the vehicles a bit,as there's no suction slot there,nor at the A2 tunnel.