Diffuser design, per Lotus blog

[Otto]

Originally Posted by freebeard

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

Here's my favorite end-plate solution:

It suggests to me that the outer half of a rear-wheel spat is superfluous.

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?

[freebeard]

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.

[Otto]

Originally Posted by freebeard

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....

[kach22i]

Originally Posted by Otto

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


The leading edge in water is a different matter.
http://www.gadgetreview.com/2012/05/the-quadrofoil.html

[aerohead]

Originally Posted by Otto

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?

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.

[freebeard]

How so superfluous?

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 -- ???

[Thenorm]

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.

[Otto]

Originally Posted by Thenorm

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?

[kach22i]

Originally Posted by freebeard

kach22i -- ???

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

A jet engine noise reduction device called a chevron, now in use on commercial airliners, is a good example of a NASA-developed technology that climbed the TRL scale to success, said Fay Collier, manager of NASA's Environmentally Responsible Aviation Project.

Chevrons are the saw-tooth pattern that can be seen on the trailing edges of some jet engine nozzles. As hot air from the engine core mixes with cooler air blowing through the engine fan, the jagged edges serve to smooth the mixing, which reduces turbulence that creates noise.

The new Boeing 787 is among the most modern jets relying on chevrons to reduce engine noise levels, sporting chevrons on the nacelles, or fan housings. The Boeing 747-8 has chevrons on both the nacelles and inner core engine nozzles.

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/


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


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.

[freebeard]

Question answered?

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?