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Old 03-23-2015, 03:58 PM   #1 (permalink)
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Chevron trailing edge applications

I am thinking for couple of months now to a possible drag reduction application of this principle: Chevron (aeronautics) - Wikipedia, the free encyclopedia
I imagine that this system that permit a gradual mixing of different layers with different velocity might work to reduce the turbulence of the side mirrors. I wonder if someone tried or heard something.
This time there is no jet on the inside of the tooth-sawed perimeter but outside, the speed inside of this perimeter being zero...
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Moving forward with this idea, similar with the utilization of "air tabs" I imagine utilization of such pattern always when the smooth surface has to be interrupted. Instead of make a clean smooth line (like the wheel passage) I imagine using a pattern like this. The intention is to not increase locally the body section.
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Last edited by calfianu; 03-23-2015 at 05:06 PM..
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Old 03-23-2015, 04:37 PM   #2 (permalink)
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Looks like the principle behind *how* a badminton "birdie" flies.
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Old 03-23-2015, 05:39 PM   #3 (permalink)
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I love it! Vortex generators with zero added frontal area and surface roughness!
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Old 03-23-2015, 05:47 PM   #4 (permalink)
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Chevrons

The NHTSA might interpret the 'tubercules' as a pedestrian safety hazard,for when the mirrors are folded and folks in parking lots are passing by,to and from shopping.
Since the serrations don't provide any boat-tailing,they may not affect the base pressure of the mirrors wake,but since there is a zig-zag differential separation line,there ought to be some significant vorticity and shearing which might break down larger eddies,kinda homogenizing the wake.This is a concept BicycleBob spoke about years ago.
These smaller eddies might succumb to quicker viscous attrition,killing the mirrors wake in less distance/time,while reducing its effect on interference drag.
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Old 03-24-2015, 10:30 AM   #5 (permalink)
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I can't help but wonder if this would make any appreciable difference on a modified car, or if it would even be remotely testable without a wind tunnel.

Of course, this begs the question, and I'm not trying to shut down this thread or anything: If something changes airflow too little to make a measurable difference, is it worth talking about?
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Old 03-24-2015, 04:13 PM   #6 (permalink)
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Quote:
Originally Posted by Sven7 View Post
I can't help but wonder if this would make any appreciable difference on a modified car, or if it would even be remotely testable without a wind tunnel.

Of course, this begs the question, and I'm not trying to shut down this thread or anything: If something changes airflow too little to make a measurable difference, is it worth talking about?
There are too many "IFs" ...
there is THIS out there... and they say it works. There are not chevrons, but it uses the boat tail effect.

On the other hand we have seen THIS

IF they work (and apparently they do), what can we do wrong by talking. You've seen the yellow parts in the picture. They are plastic "Kinder Surprise Egg". Any ideas to test their drags using household stuff ?
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Old 03-24-2015, 05:24 PM   #7 (permalink)
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It's good to see you posting again. I thoroughly enjoyed http://ecomodder.com/forum/showthrea...gns-25119.html.

One picture I have squirreled away in an album called freebeard's Album: pieces and parts is this:


What I read at the time was that the main effect is acoustical. This is a valid consideration for the rear-view mirror. And it also suggests ways to test it with common house-hold appliances.
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Old 03-24-2015, 05:33 PM   #8 (permalink)
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'this'

Quote:
Originally Posted by calfianu View Post
There are too many "IFs" ...
there is THIS out there... and they say it works. There are not chevrons, but it uses the boat tail effect.

On the other hand we have seen THIS

IF they work (and apparently they do), what can we do wrong by talking. You've seen the yellow parts in the picture. They are plastic "Kinder Surprise Egg". Any ideas to test their drags using household stuff ?
That's a box-cavity behind the mirror.It captures a vortex,allows a pressure rise,reduces the wake,and increase base pressure, while adding length (fineness ratio ).
It's good thinking.
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As to the serrations,again,they don't do anything to increase the base pressure per se,but the shearing forces due to the zig-zag separation line might make for 'mixing' and breaking up larger turbulent eddies into smaller,more homogeneous eddies,which dissipate sooner.
*They could be modeled at 1:1 scale with DNS CFD on a $100,000,000 supercomputer.
*And they could be measured at 1:1 scale in a good wind tunnel,looking each time at total drag for a change.
*I don't have any confidence that we could measure their effects 'at home.'
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Old 03-25-2015, 03:33 AM   #9 (permalink)
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Quote:
Originally Posted by aerohead View Post
That's a box-cavity behind the mirror.It captures a vortex,allows a pressure rise,reduces the wake,and increase base pressure, while adding length (fineness ratio ).
It's good thinking.
Hmmm that reminds me, some cars have much longer (in the sense that you used the word "length") mirrors than usual but some lowish drag cars have your typical flat brick shape mirror, does adding extra length help a lot? I'm guessing it's not more common because you have to pay attention to interference drag if the mirror is near the A pillar.
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Old 03-25-2015, 06:58 AM   #10 (permalink)
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I'm not sure if used on a leading edge it would also be called a "Chevron", but I know it works.

I did it on my hovercraft splitter years ago, it helped reduce the noise by spreading out the sound nodes and lower their peaks.

Hovercraft - Experimental Skirt Project - Page 2 - Boat Design Forums






Adding air to a stream at lower pressure by increasing the velocity is what I did on my S-10 pick-up roof wing.

See link in signature below.

It would be interesting to see some specific ideas and applications (sketches).

Personally I don't feel motivated to develop a hybrid idea (combining ideas from previous projects) without a goal in mind.

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