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Old 04-25-2015, 09:45 AM   #1 (permalink)
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Window Screen as a Skin Material

In a recent tread the topic of fabric covered structures and flexing came up. An odd thought or open question popped into my head early on a Saturday morning after a stiff cup of coffee.

Background:
On some belly pans people have wondered about using metal screen under the exhaust pipes and mufflers. The thinking is that the screen is closed enough to allow most air to pass by it, yet allow heat radiation to penetrate outward.

This concept has been dismissed if I recall correctly because the exhaust/muffler would bake the underside of the car by not getting enough cooling airflow over the hot exhaust surfaces.

If most air passes over a tight weave metal screen, could then a metal or plastic screen be used as a fabric covering, lets say on an aero-shell over a pick up truck bed? This of course would have a lattice structure of some kind (wood, plastic, aluminum) under it, perhaps a 12-inch on center grid to secure to.

One advantage is that you can see though a screen, the other is that it's light weight, and finally it is low cost.

I can imagine that it is easy to work with and secure if proper seamstress-like measures are taken.

Cross winds would just pass thorough, but the main flow of air passing over the body would be at lower pressure and higher velocity, following the skin contours.

Just a wacky idea, please discuss.

One simple "hands on" experiment could be to take an old screen and a blow dryer and see at which angles of attack the air flow penetrates and when it deflects or aligns with the screen plane. The wetting of hands or using heat could make this a very "hands on" experiment indeed.

It might be the coffee talking, have fun with it.

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Last edited by BabyDiesel; 04-25-2015 at 09:54 AM.. Reason: Misspelled word
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Old 04-25-2015, 11:24 AM   #2 (permalink)
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Sounds like a good experiment to use wool tufts with.
BTW, There is screen that is tougher than your average screen. It is designed for people with pets, and they sell it at the big box hardware stores.
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Old 04-25-2015, 08:31 PM   #3 (permalink)
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Screen comes in different mesh sizes and materials from nylon to steel. A great deal of experimentation will yield some fascinating possibilities.
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Old 04-25-2015, 11:30 PM   #4 (permalink)
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Air blowing over a mesh fly screen makes and awful lot of noise. Perforated 1.6mm aluminium might work better.
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Old 04-26-2015, 03:48 AM   #5 (permalink)
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I don't know the background behind this, but in the lower left is an illustration of 'passive porosity'.

I agree that perf metal might work well, but the acoustics could be problematic.

Edit: OK, Google knows about 'passive porosity:

https://archive.org/stream/nasa_tech...ge/n7/mode/2up

http://www.google.com/patents/US6616218

It even points back to where I found the chart:

http://ecomodder.com/forum/showthrea...tml#post391013

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Old 04-26-2015, 09:44 AM   #6 (permalink)
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Good input guys, I had not thought of the noise aspect. A windy day sure makes that front door screen on my house sing like the devil. Have to wonder if the noise would be any more or any less than tire noise we have grown accustomed to on the highway.

Perforated aluminum would be an interesting choice. I once built a work station booth-like enclosure upon which I could hang my drawings while working on my drafting board. Three feet away you could not see much though the panel (perforated steel), but at six feet, 20 feet........ the more the distance, the more transparent it became.

The links Freebeard provided mentioned a possible additional benefit I was unaware of.

Quote:
The device minimizes the strength of the separation in the base and wake regions of the ground vehicle, thus reducing drag.
It's sunny here, gotta get out and enjoy it. Will return to this thread soon.
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Old 04-26-2015, 08:10 PM   #7 (permalink)
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Quote:
Originally Posted by kach22i View Post
Good input guys, I had not thought of the noise aspect. A windy day sure makes that front door screen on my house sing like the devil. Have to wonder if the noise would be any more or any less than tire noise we have grown accustomed to on the highway.
Remember though , noise= drag.

You can buy 1.6mm alu thick perforated sheet that's used in making window security screens. I'm using some to hold up the flexi solar panel on my van. Because the material is more solid than a pure mesh, air should flow cleaner over it, while still allowing some ventilation/ heat exchange.
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Old 04-27-2015, 06:08 PM   #8 (permalink)
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screen

*on the belly,the air would be flowing parallel to the ground.If the belly were sealed above the the bottom of the pan,any opening would be seen as a pool of dead air (upside down) and the air would just skip over it like a flat stone on smooth pond.
*Since a void cannot support flow,the perforated panel may act no better than the void it's covering.It could introduce turbulence.
-----------------------------------------------------------------------------
*On a streamlined bedcover,the solid surface furnishes a deceleration ramp,to slow the air and build its static pressure so when the flow does detach at the back,it's at a higher static pressure,increasing the base pressure,and reducing pressure drag.
*If you use a perforated skin,it cannot perform the pressure recovery,as all the pressure will be equal to that just behind the cab,where it's the lowest,imparting the lowest pressure to the wake,and maximizing pressure drag.
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Old 04-27-2015, 06:36 PM   #9 (permalink)
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Fabric/textile/flexible skin in automotive industry and lightweight engineering.

The auto design and textiles industries at work.

EDAG;

News-Detail: EDAG Engineering GmbH



BMW;

Chris Bangle's famous flexible/flame-surfacing model.

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Old 04-28-2015, 09:44 AM   #10 (permalink)
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Quote:
Originally Posted by botsapper View Post
The auto design and textiles industries at work.
I love the architectural connection in that first video.

A previous patent quote:
Quote:
The device minimizes the strength of the separation in the base and wake regions of the ground vehicle, thus reducing drag.
I think that the patent works minimizing the strength of separation because the pressure is lower, and not higher across the screen material.

aerohead
Quote:
a void cannot support flow..............a perforated skin....cannot perform the pressure recovery
Perhaps the lack of pressure and adherence to the surface is not an issue because the air will still flow along a surface which in parallel appearances is solid, and not perforated as it looks to be at right angles.

It is still healthy to question, right?

I'm sure aerohead is right, and that failed experiments don't get published as often as successful ones, so we might not find about about this concept that way.

However I think it may be worth doing at least a hair dryer experiment, if nothing else to get it out of my system so I can move on.

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Chin Spoiler:
http://forums.pelicanparts.com/off-t...effective.html

Rear Spoiler Pick Up Truck
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Roof Wing
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