Diffuser design, per Lotus blog
 

http://www.lotustalk.com/forums/atta...o-005-copy.jpg
and
http://www.lotustalk.com/forums/atta...o-006-copy.jpg

Major improvement by vertically extending outermost diffusers almost to ground level behind rear tires, otherwise apparently the flow past rear tires converges so as to bugger the flow closer to centerline such that it is poor.

Pls. read and consider, then comment.

Interesting. I love the more recent generation of Lotus's with the Toyota engines. They have ditched the luxury items and concentrated on making the cars fast and fun.

Those end fences are probably important to all diffusers to some degree, but I would think they are especially important for extra-steep diffusers such as the Lotus has, all the way to not very important for shallow diffusers like Hucho describes.

The spinning air coming off the rear wheels interferes with the adjacent air fence/ diffuser/strake no matter the angle of incline.

The turbulence coming off those wheel wells can be seen in may CFD images and well as some smoke ones, including the ones on the second page of the article.

It wouldn't be hard to make a Prius-type rear wheel fairing (but larger and extending further aft)--a sort of end plate or flow fence that also acts as wheel fairing.

Perhaps the large Lotus end plate enables use of a much steeper diffuser angle?

BTW, anybody here read or know of Simon McBeath, the source of the latest Lotus mods?

I just did an image search on the name "Simon McBeath", appears to be the author of several handbooks (5).

Simon McBeath - The Tuners Group
http://www.tunersgroup.com/images/large/large2008.jpg

Impressive article.
The next mod on the Jetta is rear diffuser, looks like I med to think about tire find like the prius but larger.

improvement
 

Alberto Morelli used the rear wheel fairings as the capping plates to enhance the performance of the diffuser of the 1978 Pininfarina/CNR research vehicle,killing two birds with one stone.

Read and considered. There's airflow over the 'roof' of the difusser?

Here's my favorite end-plate solution:
http://ecomodder.com/forum/member-fr...bonnevette.jpg
It suggests to me that the outer half of a rear-wheel spat is superfluous.

Had to comment, that Corvette is so beautiful in that configuration. :o I wonder if they had room to remove some more drag by extending the tail from the bottom as well.

Also I think in the Exige if you have the exhaust go out over the diffuser, then you remove the panel that blocks part of the engine bay, and you'd have some airflow due to the side intakes. Though, Lotus side intakes look horribly un-aerodynamic.

How so superfluous?

Seems to me, it would be even better to fair the rear fender aft of the wheel by adding another surface flush with the trailing edge of the tire, curving back to meet the trailing edge of the aluminum plate: Essentially a curved V to fair the flow off the rear tire to gently join the under-car flow coming off the diffuser.

And, add a front air dam extending groundward flush with the leading edge of the front bumper cover, with no concavity under the nose, plus a ~4" splitter.

Thoughts?

My understanding is there are limits imposed by the technical rules. For instance the endplates can be a specific size, they just rounded the corners on the maximal rectangle.

Hmmm.

I wonder what (if any) improvement would be if the trailing edge of the diffuser plates had a serrated edge....

The trailing edge treatments as now found on some jet aircraft engines and my own hovercraft leading edge splitter/diverter experiments back in 2008 were based on breaking up the sound nodes or peak frequencies which account for perceived loudness by distributing the sound energy across a wider spectrum and leveling it out some.

Sample:
Hovercraft - Experimental Skirt Project - Page 2 - Boat Design Forums
http://i184.photobucket.com/albums/x...22i/Wave-1.jpg

The leading edge in water is a different matter.
http://www.gadgetreview.com/2012/05/the-quadrofoil.html
http://www.gadgetreview.com/wp-conte...ft-650x487.jpg
http://www.gadgetreview.com/wp-conte...-5-650x485.jpg

thoughts
 

It would be a much improved design,but the SCTA rulebook wouldn't allow such mods for this racing class.It's akin to NASCAR's body template regulations.

In theory, you are correct. But how much would you gain? IMHO the wheel well turbulence, denied entance to the wake, would spill outward and at the rear edge of the end-plate would be mangled (flattened) and mixed in there. Simpler and it doesn't compromise the difusser.

Then there's all that salt and chunks of tread that won't build up.

Re: The rules—that was the only car I saw that had fences that weren't longitudinal, which is suposed to be a requirement. But it passed tech inspection.

kach22i -- ???

wheel wells are high pressure areas, it seems good (At face value) to leave an open path rearward to let that air into the low pressure wake while not letting it adversely disturb the air flowing through the diffuser. I read one study about ducting air from the rear wheel well out through the trunk area into the rear wake.

Hmmm.

Friend of mine with a Corvair thought the wheel well to be a low pressure area, so made a conduit from the engine bay to evacuate hot engine bay air. Worked, did not flow in reverse, he said.

So, wheel bays high pressure or low pressure?

I was addressing Otto's question based on the assumption he and others had knowledge of the now commonly used noise reduction used on jets.

News, Current Space updates, Rockets,Constellation,Satellites,Space Research,: space shuttle orbiter
http://1.bp.blogspot.com/_1q-d5V0emL...le+orbiter.jpg
the jagged edges serve to smooth the mixing, which reduces turbulence that creates noise.

What that description fails to explain is that varying distances expand the noise energy over a wider spectrum (via traveling distance) thereby taking the loudest peak down. It is after-all our hearing perception which indicates loudness by the highest frequency peak within our hearing spectrum.

Otto was imaging wheel pants or wheel fairings with a saw-tooth (serrated edge) pattern.

The only advantage I know of is because of sound (or cutting).

http://weaponsedge.com/how-to-sharpen-a-knife/
http://www.knifedealsplus.com/media/SERRATED-EDGE.gif

Question answered?

In nature there is the bat wing. Has more to do with bone structure and tensioned membranes than aerodynamic advantages I believe.

http://krisallegra.blogspot.com/2012...g-helping.html
http://1.bp.blogspot.com/-YG3SeRI2_6...00/anthro1.JPG

If the bat's wing shape cuts down on sound so that it can silently hunt insects, then all the better I guess.

On a car, tire and engine sound is going to heavily outweigh aerodynamic sound in my opinion.

It was a good answer, but the question sucked. :) Better stated it would have been, " Wuts a Quadrofo?" But I liked the picture of the serrated bypass. Much better than the line drawing I've got squirreled away.

Bats are quieter than owls?

nah, owl wins. an owl is so quiet, even it can hear itself

I walked past a Tesla Model S today and noticed the rear end seems to follow the "philosophy" described here. Strakes extending down from the diffuser where the inside of the wheel is, and the bumper actually goes inward behind the rear wheels. Food for thought.

Great big photo of that Tesla -S detail here:
http://image.motortrend.com/f/roadte...w-at-track.jpg
http://image.motortrend.com/f/roadte...w-at-track.jpg

Speaking of Model S, here is a proper picture of that diffuser :)

ummmmmm food for thought. if i could do something similar on my motorhome would hope for more stability in crosswinds. dont suffer from rear end lift if anything rear end lift would benefit handling but saving fuel and being more stable in cross winds would pay bigger divdends. all this will have to wait until i have built my new exhaust. details on idea for exhaust will be posted in appropriate forum.:thumbup: