sawtooth trailing edge

[lunarhighway]

Serrated trailing edges for improving lift and drag characteristics of lifting surfaces - Patent 5088665

i'll have yet to read this trough very carefully but this looks very much like what i mean!

[Xringer]

For cd, I can guess how that might work on the trailing edge of a swept-back wing (jet fighter). Instead of generating one massive vortex behind each wing tip, a bunch of 60 deg saw teeth cause multiple small vortexi all along the TE..?.

When this topic first came up, it really got me thinking that my CRV rear spoiler+wake boards should have some 60d saw teeth added..

And this morning while planning the micro-front wheel skirts, I made this
edit:

(Tape holding a crescent of coroplas).

Not smooth at all.. But, would cutting a sawtooth pattern in the TE & LE of the opening be beneficial to cd??
(With the teeth points orientated in the direction of travel of course).

Hehehe! Something like that is going to be considered a real eye-sore by my wife!!

[lunarhighway]

it's worth a try, but remember aero is a complex matter, what works in one area may do the opposite in another area.

A common front wheel well wayout on low drag cars seems to be a mild traditional flare out in front of the wheel, and an indent behind the wheel. it would seen that you don't want to obstruct air from getting out of the wheelwell, but some obstruction in front of the wheel is good. so perhaps you may want to experiment with leavint the rear leg of the upide down U-shape off so that the air could exit there.

just an idea

[tasdrouille]

Originally Posted by lunarhighway

it's worth a try, but remember aero is a complex matter, what works in one area may do the opposite in another area.

A common front wheel well wayout on low drag cars seems to be a mild traditional flare out in front of the wheel, and an indent behind the wheel. it would seen that you don't want to obstruct air from getting out of the wheelwell, but some obstruction in front of the wheel is good. so perhaps you may want to experiment with leavint the rear leg of the upide down U-shape off so that the air could exit there.

just an idea

You are right about the wheel openings. It is the same principle as sunroof spoilers. The goal is to get a spoiler just high enough so the flow reattaches asap past the opening. They added leading front wheel openings extensions when they did the aero development of the z06 corvette. I wonder why they just didn't design the bumper and fender accordingly in the first place though.

[Xringer]

I see what you guys mean.. Like the Jetta taped front wheel wells, just posted:
http://ecomodder.com/forum/showthrea...mods-4869.html

When I drew the trailing tail of the crescent, I was thinking about the benefits of the pizza pan wheel cover. How do they help??

Maybe, fast air flow from the front end would bridge the forward gap and flow mostly unimpeded over the tire and smooth wheel cover, then bridge the gap on the trailing end of the tire and onto the door.

If a large gap exists, fast air over the tire will pull air out of the wheel well and increase the turbulence across the door and down the whole side of the car. That gap could be the point where a big separation of flow occurs..
http://us1.webpublications.com.au/st...0/1023_9lo.jpg
http://photos.revolution-press.com/J.../veyron_12.jpg

If the upside down crescent was really close to the tire, with a really small gap, with a moon disc installed, how much different would that be from a full skirt??

[aerohead]

Originally Posted by lunarhighway

Serrated trailing edges for improving lift and drag characteristics of lifting surfaces - Patent 5088665

i'll have yet to read this trough very carefully but this looks very much like what i mean!

It appears that he uses them ahead of the wing,as with a Fieseler Storch,after the wing,but ahead of the flap,and also at the end of the flap on wings chopped at up to 20% of the cross-section for the flap.No performance claims are listed.

[trebuchet03]

I didn't see this in the thread.....

At least one computer fan mfr makes "sawtooth" blades - really, staggered notches..... But the claim is for noise reduction....



Noctua.at - sound-optimised premium components "Designed in Austria"!

They do also claim higher efficiency..... But, it's not a uniform notch - each successive blade has a slightly different offset from the last. So cross application is questionable.


Of course, we could very well be dealing with different Reynolds numbers etc. etc.


With respect to the Dreamliner nacelles.... So the claim too is to reduce noise.... It takes energy to make noise - energy that doesn't make you go forward... But the sawtooth allegedly breaks up larger vorticies... So to do that, I suspect it takes energy. If you use energy to cancel out other acoustical energy - I imagine there's a penalty. Think of luxury car acoustical noise cancellation or noise canceling headphones - it costs power to do it, but you'll experience less noise. This is just intuition speaking here The accuracy of that is all up for discussion.

I guess it's worth mentioning the very strict noise regulations for aircraft taking off

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Personally, rather than playing with funky edges/passive control - I'd like to see more research and testing on active flow control. Hyundai apparently has a cool feature in one of their cars that scoops air from under the car and blows it out small vents (at higher velocity) in the tail lights to combat the intersecting surface flow shenanigans back there... Aptera dumps their exhaust out the tail in a similar fashion too for related reasons....

[Christ]

Has anyone seen the Pagani Zonda S? I doubt it's purely aesthetic that they have 4 tail pipes arranged in a square dead center of the height of the vehicle... not the vehicle's body height, but from the ground to the top of the roof-line, I believe.

Something about that says "high velocity flow to combat vacuum at the rear of a vortex" to me. in fact, I believe it absolutely screams it.

Having a side-exit, or even rear-side exit exhaust is a blatant waste of an aero-tool that should be utilized. Someone write congress.

[markweatherill]

Heavens! It'd be easy to bolt on a tailpipe trim piece to a stock exhaust to redirect flow upwards, or centrally. On cold days you'd see the effect.

[Christ]

I'd think there's a little more involved in it than that, exactly... like legality issues with having exposed sections of exhaust beyond the bumper... illegal in PA.

However, for testing purposes, it might work out... so if it's legal for anyone, maybe a test is in order of different placements of the exhaust flow compared to the dynamic airflow of their particular chassis?

I'm thinking that even light-throttle exhaust flow will counteract a certain degree of wake caused by not having a sharp point to detach flow... plus, on a sedan (full trunk) configuration, having exhaust gasses contaminating that airspace between the upper deck and bumper cover might actually cause a flow extension, allowing the flow to stay attached to an artificial surface far beyond that of the actual sheet metal of the car's chassis.

Obviously, the exhaust gasses are under pressure, so would that not have the added benefit of canceling the vacuum space that traditionally tails an auto? Adding any kind of pressure to that area has to be aerodynamically positive, yes?