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

[euromodder]

Originally Posted by Cd

This makes me wonder what would have caused such a drastic rise in drag to .288

It's not a 3L version they started with, and a different tunnel.

Originally Posted by Piwoslaw

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

What surprises me is the effect, considering it's only a small modification - Certainly compared to full boat tails or Kammbacks.

Originally Posted by Piwoslaw

Plus a lighter rear seat. Did it also have lightweight (magnesium) suspension elements? This, of course, doesn't effect aero.

The A2 and Lupo 3L both had some expensive weight reduction measures incorporated, while still looking the same as the regular versions.
This led to their excessive price and the weak market response.

[euromodder]

Underfloor Wheel Arch Blanking

They don't seem to have a mechanism for allowing the wheels to turn though ?
Closing the gap is easy, making it actually work is something else again.

What they didn't do is fit covers on the insides of the wheel, or easier, fit a vertical blanking plate "fencing off" the inside wheel cavity.
This would need to fit close to the wheel, and be fitted on the suspension so it moves along with the wheel.

[euromodder]

What is even more surprising is the fact that the 2° diffusor helps.

On this kind of station-wagon-like rear ends - no diffusor at all ( 0° ) was found to offer the lowest drag, with a cavity, the diffusor helps another 6%.

A rear cavity is something that I could easily fit on Hägar.
A bit of foam and double-sided tape will do.

[jtbo]

Originally Posted by euromodder

What is even more surprising is the fact that the 2° diffusor helps.

On this kind of station-wagon-like rear ends - no diffusor at all ( 0° ) was found to offer the lowest drag, with a cavity, the diffusor helps another 6%.

A rear cavity is something that I could easily fit on Hägar.
A bit of foam and double-sided tape will do.

It is not very box like when you look at the roofline, for me it looks like more of hatchback etc from rear roof section.

With addition of rear cavity it is more like boxed from rear. Before cavity they used 7 degree diffusor, but with cavity 2 degrees was optimal, so if I'm not horribly misreading that would also tell that they did move from coupe/hatchback to boxed end, however it is much smaller boxed end.

High side window line and blunt front are perhaps what makes illusion of car being box shaped, sides are also rather straight down and it is relatively tall compared to width, but if one photoshops everything under window line away it is not boxed station wagon shape at all and what affect to diffuser angle is how upper side, roof, trunk lid etc are angled from top, afaik.

This should make it easier to see how it is not station wagon kind of shape at all (extract from document mentioned in 1st post):


That is one of the pits easy to fall with aeromodding, they use lot of tricks with cars that cheat eye, to see true shape and form sometimes one needs to take photo and edit it a bit.

[California98Civic]

Originally Posted by paulu

This was just one presentation from the "The Aerodynamics Challenge Dissemination Event on 19 October 2011"

Some more presentation can be found here :
Coventry University - The Aerodynamics Challenge

I missed that this had been added to this thread and added different thread to share the larger list of links when I found them: http://ecomodder.com/forum/showthrea...ies-21204.html. Moderators seem to think there's enough difference to keep them separate. Thanks Vekke for your original post. I have a new mod that I can consider for my coupe instead of the Kamm.

[euromodder]

Originally Posted by jtbo

This should make it easier to see how it is not station wagon kind of shape at all (extract from document mentioned in 1st post):


That is one of the pits easy to fall with aeromodding, they use lot of tricks with cars that cheat eye, to see true shape and form sometimes one needs to take photo and edit it a bit.

The roofline drops on most cars these days - even on my boxy Volvo V50 - though not always as much as on the A2.


The box cavity should be an easy mod on a square-backed wagon though.
It won't be as efficient without a bellypan though.

[jtbo]

Originally Posted by euromodder

The roofline drops on most cars these days - even on my boxy Volvo V50 - though not always as much as on the A2.


The box cavity should be an easy mod on a square-backed wagon though.
It won't be as efficient without a bellypan though.

Roofline indeed drops on many new cars and as air has no idea of knowing if car is wagon or not, then it might be misleading thinking that all wagons should have diffuser at 0 degrees, if roof drops, then it is not wagon in sense of aerodynamics and I think that one must pick more appropriate form from this image Sven posted to other thread:
http://ecomodder.com/forum/showthrea...tml#post296642

Most of such examples were made at time when wagons were truly boxed shape, so that is why wagon is shown to have 0 degrees at optimal diffuser angle, but it might mislead modder to think that all wagons should have that as new stuff indeed has angle, so it can't be true anymore with all wagons.

So when one puts on boxed cavity to rear, one need to put diffuser, that is closer to 0 degrees, but without boxed cavity diffuser must be more angled if roofline drops, when roofline does not drop 0 degrees is best, how about boxed cavity on boxed rear end without dropping roofline? I guess 0 degrees still?

This leads to thinking that boxed cavity turns dropping roofline to be more towards boxed shape, but as it makes it smaller boxed shape it will be improvement to efficiency.

Or something like that. Most important to know would be just that there are no absolutes and it is impossible to generalize, every situation must be examined separately, but understanding why some forms require certain angle is helpful to make right judgement of what angle is going to work or which things will never work.

[ecomodded]

The 100mm extrusion is interesting along with the rear diffuser in that they are 'behind' the wake yet effect it, the 2" diffuser is particularly effective , I am assuming it could be used with other Kammback designs with similar results / success.

[UltArc]

None of those four are available. COME ON SON!

Thank you, Metro, for saving some of it. UGH.

[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.