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...
Attachment 17222

Attachment 17223

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.
Attachment 17224

Looks like the principle behind *how* a badminton "birdie" flies.

http://i146.photobucket.com/albums/r...psjxam5uyq.png

I love it! Vortex generators with zero added frontal area and surface roughness! :thumbup:

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.:)

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 ?

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:
http://ecomodder.com/forum/member-fr...29-0-large.jpg

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.

'this'
 

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.':(

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.

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
http://i184.photobucket.com/albums/x...i/CONE-3-1.jpg
http://i184.photobucket.com/albums/x...22i/HOV105.jpg
http://i184.photobucket.com/albums/x...22i/DUCT-1.jpg
http://i184.photobucket.com/albums/x...22i/Wave-2.jpg
http://i184.photobucket.com/albums/x...22i/Wave-1.jpg

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.

I've been considering using these ebay rain guards for some time:

Universal Rear View Side Mirror Rain Board Shade Shield Water Guard | eBay

My reluctance is due to the fact that I won't be able to test the difference to see if they actually work.

Looks like you could make a set from a plastic milk jug or a 2 liter soda bottle and attach it with some very high bond tape (3m VHB). ;)

talkin' about
 

If the DOT won't let us do the camera system replacement,then I suppose that there's gonna be a lot of dialogue about potential technologies and their savings with mirrors,and no stone will be left unturned.
Olsson,at Chalmers University did say that his scale model testing ought to be followed up with full-scale testing in order to optimize all the interactions.Something that can't be done at small scale.
The car/mirror must be evaluated as a system.We won't be able to attach mirrors to a wind tunnel wall or sting and learn anything.
What's worse,each car is different,so there isn't going to be any one-size-fits-all solution.
Since there are hundreds of millions of vehicles on the road,the energy department and EPA may be interested in mirror R&D to mitigate waste/air pollution.
The more streamlined the cars become,the more important the mirrors become.

noise
 

In NASA's study of the silent flight of owls they mention the wings leading edge 'comb',the trailing edge 'fringe',and the downy feather sublayer which dampens turbulence.
In our modern aerocoustic wind tunnels we've got a great opportunity to tune out some noise as is happening already with side mirrors.
Also,I notice Ford SUV rear bumper fascias resonating as they go down the highway,beat up by the buffeting of the wake.If they'd run faster tunnel velocities,they'd see this and fix it before it makes it into production.:p

length
 

I don't have a pictorial to share,but here's some data to think about.
*Kach22i's prop spinner is about Cd 0.30 in a free stream of air.
*If you put 1-soup can(same outside diameter) behind it,it drops to Cd 0.233
*If you add a second soup can ,Cd 0.225
*Adding a 3rd can,Cd 0.215.
*Mair's boat tail wind tunnel model,with prolate ellipsoid nose and 3-soup cans was Cd 0.204.
*The 'GAVRE',Aberdeen,5-degree boat-tailed artillery projectile is Cd 0.16 in subsonic flight.

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So length does matter,aerodynamically.
The 1996 Porsche 911 GT race car has very 'long' elliptical mirrors,far from the body.My opinion is that Porsche spent a lot of tunnel time developing these LeMans mirrors.
Only full-scale testing or DNS CFD is going to show us the way.
The A2 or DARKO tunnels would be perfect for us.They're both capable of 1-count accuracy and perfect repeatability.

Hmmm...0.3 is not bad considering that's only a little bit more than the average body drag right?

I noticed modern Porsche mirrors are 1 soup can longer than the typical brick shaped mirror, I wonder how much drag that cuts out. With the 911 coming in at Cd 0.27 with ginormous 275 width tires, they have to be doing something right.

Porsche
 

There's a lot of competition for Porsche customer dollars/euros/ etc.. and I suspect that Porsche owners have expectations that they have kinda leading -edge technology on their cars,including the mirrors.So I suspect that what we see is quite intentional.
I'll look at their mirrors next time.But I agree with your assumption.0.27 is really a coup,considering where they've been since 1939.

Great information.

I posted for the wavy edge treatment, but got more.:)

For the record, I made the spinner cone as long as I could without infringing on the rudder vanes.

Also making the cone any longer than the duct might not be the best approach, but does pause for consideration.

The frictional skin drag losses from building a longer duct might negate benefits of straighten out the swilling trust flow.

However the added weight of a longer thrust duct and spinner, and weight so aft of the center of gravity are unforgiving realities on a hovercraft.

.................................................. .................

Back to side view mirrors; length, weight, and obscuring forward peripheral vision all must be weighed in the designer's mind. Just as other factors concerning the hovercraft tail cone.

.....................................

Saw-tooth or wavy edges may become a fashion at some point, just as with golf ball dimples.

We should be careful about what we wish for, right?:thumbup:

Or on a PC if you spend a few hundred on a GPU, and do some programming :-)

PC
 

As I understand it,DNS can only be performed with a supercomputer,working in teraflops.
The mesh size and time steps are so vast that a PC cannot possibly handle the volume of information.
It is not a matter of a graphical processing unit.
The Full Navier-Stokes equation works in a spherical coordinate domain.It's millions of individual points in space,defined each by X-Y-and Z coordinates, which are interacting and solved for simultaneously in Eulerian differential calculus.All turbulence must be modeled,something only DNS can perform.
There is a RISC computing approach involving perhaps dozens of parallel computers operating together,and their cost,for DNS capability,as of 1992 was over $100,000,000.
DNS is quite old.It's only until recently that computers attained the speed and capacity to take on DNS.
Daimler-Benz' supercomputer requires over 48-hours continuous run time to analyze a single car.
The other thing about PCs is that,we need a digitized full-scale car with every,and I mean every small detail,down to the fraction of a millimeter.
I know of only Southwest Research Institute,in San Antonio,Texas which has the capability to do this.I've no idea what the cost would be,or if one could even gain access to their facility.
No doubt,Moore's Law will,over time,bring PC capacity up to otherwise 'impossible' levels,but I don't want to predict when they'd attain 'super' status.

So, if we make super-long mirrors, our cars will be more aerodynamic? :)

A super long mirror would weigh more, obscure vision more and has diminishing returns based on speed. If you were going near supersonic speeds perhaps it would make sense to go much longer.

I like the idea of looking to what Porsche does as a leading indicator for what optimum length is might be a good one in my opinion.

I think we need to keep in mind that cars turn at speed in tighter circles than aircraft and boats. Some of our design consideration should for off angles or "cross wind" conditions. This means excessively long bodies and lengths may be a liability under some conditions.

Just my opinion.

super-long
 

I think Kach22i has made a good list of 'practical' considerations for design.
Hucho would 'optimize' for a shape.As soon as a feature got drag to 'saturate,' he'd quit and move on to another feature.
*The mirror,1st of all,needs to provide the optical pathway we need for safe motoring.
*So the design needs to respect that.
*Manufacturers would target something like the 99th percentile for human factors in their design.
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*I have notice that,say for Toyota,many of their side-view mirrors are identical in 'design',but scaled for each vehicle 'size' as if respecting that a pair of ears on a mouse should be proportioned like a pair of ears on a deer.
*The Echo mirror looks just like a Corolla,Camry,Avalon,Tacoma,T-100,and Tundra,but a smaller size,as if the human eye behaved differently from vehicle to vehicle.
* I might install Echo mirrors on the T-100 and have basically the same optical performance,but with a smaller frontal area (CdA).
*A random thought is about the CLA 180 M-B Blue-efficiency car.It's Cd 0.22 side mirrors are lower drag than the other CLA cars.Whatever they've done would be a tip off to us as far as low drag mirror tech.
*Also check out the new VOLT/Enclave/FIT/Cadillac CTS/BMW/Lexus............

super-long could look good..
http://img168.imageshack.us/img168/8461/garage2fb6.jpg

WD40 ... you know, each time when I was drawing a car, I felt this is the only way the mirrors should be designed. Integrated. We've seen this idea applied on many vehicles, but the latest with high aerodynamic performance gave up this idea. From aesthetic point of view, this approach is my only choice. And, if the future will bring cameras in the place of mirrors, I would integrate them in the same way.

I think we need more pictures.
http://www.ausmotive.com/images2011/...1-leak-05s.jpg

As you can see, if you took the windshield's curvature and extended it a few inches to the side of the car, that's about where Porsche's mirrors start, the shape is like a "bullet" that goes back and is cut off at the place where the driver expects to see a mirror out the window.

Compare to the new Corolla: http://images.autotrader.com/scaler/...lla/230550.jpg

A blunt, flat angled rectangle shape. A few inches shorter overall.

I wonder, how might one add length to the front of that Porsche mirror without increasing interference drag? Maybe extend the "bullet nose" forward and curve it in a little?

The Lexus LFA has really wild looking mirrors and they claimed it helps aerodynamics, but they're about as long as the Porsche mirrors: http://www.blogcdn.com/www.autoblog....lfa-review.jpg

I think the Nissan GTR also supposedly had aerodynamically tuned mirrors:
http://www.nissanusa.com/content/dam...051x-large.jpg
Also short and stubby!

Finally, the McLaren P1, a car that supposedly had every body detail carefully designed:
http://upload.wikimedia.org/wikipedi..._Show_7847.JPG

Looks a lot like the Porsche mirror!

with an ordinary shape this W124 Mercedes has a Cx=0.28.
http://upload.wikimedia.org/wikipedi...r_20080315.jpg
Same for Opel Vectra B2:
http://upload.wikimedia.org/wikipedi...t_20080118.jpg
While the 0.26 Opel Calibra has half "integrated" mirror (the mount side), leaving half "separated".
http://upload.wikimedia.org/wikipedi...t_20071212.jpg

Reading aerohead's observation about "base pressure" another idea (hopefully the last one)regarding the reduction of the drag of these mirrors. I am not sure I got the right understanding about "base pressure", but these movies will explain the idea better than words. In few words is about a mirror that becomes "porous" or "permeable" to avoid a low pressure area formed on the reflexive element.
https://www.youtube.com/watch?v=uSwQ...ature=youtu.be
https://www.youtube.com/watch?v=mEdA...ature=youtu.be
https://www.youtube.com/watch?v=tpDa...ature=youtu.be

What's the premise? One seems to be a flat plate in a cup, and the others—segmented mirror elements with air gaps? I don't see how the air is introduced.

And how do you generate the [hexidecimal?] number to name the videos?

I think the air is introduced through a hole at the front.

In rain, I would imagine the spray of water coming out the mirror gaps to make them impossible to see?

You-Tube video
 

*It's 2-D and that's problematic for side flow which affects the overall flow.
*The Reynolds number is low,giving a laminar boundary layer.
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*The 2-D might give some insight and steer design.
*Full-scale tunnel or DNS CFD at 'road-going' Reynolds number is necessary for accuracy.
*The mirror must be on a particular vehicle,and it's performance will be for that particular vehicle only.
*It is the interaction with the vehicle which is most important,not an isolated mirror attached to a wall.