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Old 09-10-2008, 05:25 AM   #11 (permalink)
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this is what wikipedia has on te naca intake

Quote:
This design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices which deflect the boundary layer away from the intake and draws in the faster moving air, while avoiding the form drag and flow separation that can occur with protruding inlet designs.
looking at this example it's hard to overlook the similarities between two vg's and a naca intake.



so it's my understanding that they work on the same principle where the vg's reënergise the boundy layer by drawing in air from outside the boundry layer and naca's draw do the same but draw in air below the boundty layer, and the skin.

this suddenly made me think that an upswept lip spoiler ofte found on sporty hatchbacks, but also on car with very low drag quoefficients could be an every simplified vg, epsecially since the once that can be suspected to be there for true aero reasons are often rounded and heigher in the middle

here a picture on my string of thoughts that might make more sence...



but then that last configuration looks like this test autospeed did
on their hoda insight and they recorded no benefit. but of course the insight is already highly optimised and might not need any band aid somutions as it's basic form is already so good... and all the separation angles are very optimised

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Old 09-10-2008, 01:11 PM   #12 (permalink)
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quiet

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Originally Posted by Otto View Post
NASA has been studying serrated trailing edges, and serrated leading edges are of interest, too. Google for it. Also, check into Barred Owls, which have serrated feathers for ultra-quiet flight. Works.
NASA's Paul Soderman sent me a paper he did from his research at NASA Ames.He had studied owl flight and I believe the premise of the work was acoustic Stealth,and not necessarily drag reduction.---------------------- At full take-off power,does the sawtooth blend the interface between the turbo-fan's jet stream and the slower surrounding nacelle air?
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Old 09-10-2008, 03:07 PM   #13 (permalink)
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Old 09-10-2008, 03:16 PM   #14 (permalink)
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Humm, Leading Edge VGs, sorta like Whale Fin Tech..

AutoSpeed link

VGs up on the nose didn't hurt the MPG, but helped the handling..
I looks like they were installed at an angle (hard to tell)..
Does anyone here know what that Insight angle might be?

I have an angled area on my skidplate that might be a good place to try some VGs!

--------


I've been thinking about making a Coroplas rear spoiler.. Maybe a ZigZag TE
would be better than trying to make it rounded like a baseball cap bill..?.
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Old 09-10-2008, 03:29 PM   #15 (permalink)
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I can't wait to explain this to friends and watch as their eyes glaze over and they get the brain-dead look on their faces, !

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Old 09-10-2008, 03:41 PM   #16 (permalink)
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lunarhighway -

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Originally Posted by lunarhighway View Post
this is what wikipedia has on te naca intake

...

looking at this example it's hard to overlook the similarities between two vg's and a naca intake.



...
Wow (again). And it's just been staring us in the face for the last few years.

EDIT: I have always wondered what the "negative volume" between two Airtabs could mean, so this is kind of neat. On a huge semi, the fact that the airtab "comes out" of the trailer may be relatively unimportant in relation to creating the quasi-naca duct.

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Old 09-10-2008, 04:51 PM   #17 (permalink)
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Quote:
Originally Posted by aerohead View Post
NASA's Paul Soderman sent me a paper he did from his research at NASA Ames.He had studied owl flight and I believe the premise of the work was acoustic Stealth,and not necessarily drag reduction.---------------------- At full take-off power,does the sawtooth blend the interface between the turbo-fan's jet stream and the slower surrounding nacelle air?

Yes. the sawtooth edge improves on the ducted fan, where the fastest inner core is buffered from the ambient air, reducing the shearing effect between layers, which causes the noise. The sawtooth makes for micro-vortices that to some extent cancel each other out, as the upside flow from one micro vortex impinges on the downside flow of the next.

Where could I get a look at the Soderman paper?

The owl, btw, uses his serrated edge feathers more for noise reduction than for most efficient lift. That's why raptors fly faster, though more noisily--they get breakfast by dint of speed and power, vs. being sneaky.
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Old 09-10-2008, 05:26 PM   #18 (permalink)
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Otto,

Suggest you go to NASA - Advanced Search and and do an Soderman, etc. search.
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Old 09-11-2008, 01:29 AM   #19 (permalink)
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Quote:
Originally Posted by lunarhighway View Post
here a picture on my string of thoughts that might make more sence...


That reminds me of a rear spoiler on a car I once raced against:


The car was very fast (low drag) and hard to draft. If I remember correctly, the driver/owner claimed that the saw-toothed spoiler made more downforce and less drag than a spoiler that was the height of the bottom of the saw teeth. His business is data acquisition systems, and his car is fully instrumented to measure such things, so I tended to believe him.

Also, when I saw the car, I believe the spoiler was about the same height but I remember the teeth as being a lot more prominent (taller), fwiw.

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Old 09-11-2008, 05:35 PM   #20 (permalink)
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Paul's paper

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Originally Posted by Otto View Post
Yes. the sawtooth edge improves on the ducted fan, where the fastest inner core is buffered from the ambient air, reducing the shearing effect between layers, which causes the noise. The sawtooth makes for micro-vortices that to some extent cancel each other out, as the upside flow from one micro vortex impinges on the downside flow of the next.

Where could I get a look at the Soderman paper?

The owl, btw, uses his serrated edge feathers more for noise reduction than for most efficient lift. That's why raptors fly faster, though more noisily--they get breakfast by dint of speed and power, vs. being sneaky.
Otto,if you can't find the paper through GOOGLE,as CobraBall recommended,I'll dig it out and mail you a copy.Might take a little time to find it but I'm pretty sure I can put my hands on it.

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