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Old 08-05-2015, 08:34 PM   #1 (permalink)
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Anyone use Porous coverings?

I've been reading and found a number of articles on the use of porous materials on the surface of square backed bodies that has a huge reduction in drag ( about 35%) due to the breaking up of the rear air rotation at the back of the vehicle and greatly increasing pressure at the rear. Any one tried this?

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Old 08-05-2015, 08:37 PM   #2 (permalink)
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Old 08-05-2015, 09:40 PM   #3 (permalink)
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This one seemed most applicable

http://www.math.u-bordeaux1.fr/~chab...li/BGM-JFE.pdf

There is also a lot research referring to wing aerodynamics ...especially noise reduction.
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Old 08-06-2015, 12:21 AM   #4 (permalink)
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Wow, scanned the link paper and it looks like the computer said it was better. I think you'd find real world testing on big things like cars would yield small results. This seems easy enough to test on a real vehicle, I wonder why it was not done? Computers are susceptible to the dreaded GIGO effect even today in 2015. It has been discussed a lot here on ecomodder mostly regarding golf ball style dimples. It is in fact the very reason I started posting on this forum cause I was thinking of dimpling my GMC pick up.
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Old 08-06-2015, 12:34 AM   #5 (permalink)
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Quote:
Originally Posted by ChazInMT View Post
Wow, scanned the link paper and it looks like the computer said it was better. I think you'd find real world testing on big things like cars would yield small results. This seems easy enough to test on a real vehicle, I wonder why it was not done? Computers are susceptible to the dreaded GIGO effect even today in 2015. It has been discussed a lot here on ecomodder mostly regarding golf ball style dimples. It is in fact the very reason I started posting on this forum cause I was thinking of dimpling my GMC pick up.
Ah yes, the problems of scale and fluid dynamics.
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Old 08-06-2015, 07:53 AM   #6 (permalink)
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Quote:
a huge reduction in drag ( about 35%)
Not possible.



Quote:
Trucks and trailers generate aerodynamic drag in four main areas: front of the tractor, gap between tractor and trailer, underside of the trailer, and rear of the trailer. Here are a few of the ways engineers have targeted these areas, along with Wood’s rough estimate of the percentage each idea is said to reduce drag: Top row: wake boards, 7%; vortex strake, 7%, high-momentum mudflaps, 3%; fairing, 3%. Bottom row: passive porosity, 4%; boattail, 5%; side skirts, 2%; and vortex traps, 7%.
This from Richard Wood "who chairs the Society of Automotive Engineers' (SAE) Truck and Bus Aerodynamic and Fuel Economy Committee and is a member of the American Trucking Association's (ATA) Engineering and Technology Policy Committee and the Technology and Maintenance Council (TMC) Future Truck Committee".

With misinformation and factually incorrect statements swirling, Richard Wood is out to ease the turbulence
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Old 08-06-2015, 12:32 PM   #7 (permalink)
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This appears to be different than golf ball dimples....

I haven't been able to find much on what materials have been used. A paper on aircraft wings said they used 30% open material for their testing. Standard window screen is about 50%....which is what I'll give a try when I find the time. It appears that the porous material is set above the skin of the object, not directly on it, creating a second air layer that also acted as a jet at the rear edge of the object, which in itself appeared to reduce drag about 13%. I am still digesting this info. Also, in contrast to Mr Wood's diagram the whole top surface and front round edge of the body was covered with the material, not just a small section of the back and the rear. I suspect covering the rear has little or no effect. A recent review (April 2014) of Vehicle drag reducing methods in The International Journal of Mechanical & Mechantronics Engineering ( http://www.ijens.org/Vol_14_I_02/145...JMME-IJENS.pdf) seem to have several methodologies aimed at breaking up the rear vortices in order to increase pressure at the rear surface of the vehicle. Interesting reading.....
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Old 08-06-2015, 01:59 PM   #8 (permalink)
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That is interesting. All the best stuff is in PDFs.

I found an infographic that shows 35% for the rear, rather than the 25% total in the one I posted. It's big, so here's the link: 11% to 12% increase in fuel economy for flat backed trucks
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Old 08-06-2015, 02:07 PM   #9 (permalink)
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I am seeing more and more aerodynamically modified trailers on the roads already---boattail extensions, wings, even a few aero wheel covers too. If this works as well as they say it does, I suppose I'll be seeing these soon too.
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Old 08-06-2015, 04:37 PM   #10 (permalink)
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2-D flow

Quote:
Originally Posted by 93tracerwagon View Post
http://www.math.u-bordeaux1.fr/~chab...li/BGM-JFE.pdf

There is also a lot research referring to wing aerodynamics ...especially noise reduction.
The paper cited concerns 2-dimensional flow which immediately disqualifies it for automotive applications.

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