Belly pan or vortex generators?

[aerohead]

Originally Posted by donee

Hi All,

I drove around for a week with tufts behind turbulators the upper 1/3 of one A- pilar. When the conditions were windless, one could see the tufts flowing horizontal on the turbulator side without any motion. On the side without the turbulator the tufts were trailing with about a 15 degree up angle and with some small oscillating motion.

Even slight cross winds completly changed this, however. If the wind came across the car, to the turbulator side, the tufts ran at a 15 degree or more up angle. So, the turbulator benefit was lost completely.

Based on this, I put turbolators on both sides of my Prius. Still, I think there is a possibility that drag is incressed with the Prius.

On cars with higher windshield rakes, the advantage may be more. The issue is that the air is pushed sideways around the edge of the A-pilar. In the Prius the air is at about a 60 degree up angle across the windshield. In other cars it may be more horizontal. When the flow into the A-pilar area is horizontal and pushes out into the slip stream by its own momentum, it will begin to turn over, and turn into vortex. The purpose of the tubulators is to use the cross flow momentum to trip the air into a slip-stream direction.

My guess is there may actually be an optimum windshield angle for vortex formation. Anybody have any info on this? Aerohead ?

donee,I don't have anything special on windshields.As there IS an angle for backlights that we're warned to avoid ( 28-degrees ),there might be a specific windshield angle which favors high vorticity but I've never read where it is addressed specifically.Sorry!
Some of the literature will claim that for drag reduction you don't need to go beyond some angle.
There will be discussion about minimum radii of the A-pillar to prevent separation.
I look at the GTP cars and high-end aircraft with compound windscreens as examples of the best technology.
Hucho eludes to them and mentions 'cost' as a reason we don't see them in production vehicles.
The flow at this area is also aggravated by the side mirrors although much less than in past generations of vehicles.
Vorticity if present,would be an expensive proposition to remedy,and since it's occurring in a favorable pressure regime I don't know if VGs would really help.

[edbso]

Originally Posted by dmac257

edbso,

What did you use for screen material. Regular al window screen or heavier stuff?? Any edging or just loose wires?

Don

Hi Don;

Used regular Home Depot screening, screwed every 6 or so inches and used construction adhesive on the edges between the screw heads.

It tore off during the last big snow storm so I replaced it with 24" roofing aluminum.

[dmac257]

Originally Posted by Otto

Why paint it? The naked screen should be adequate to smooth the air flow, while allowing the exhaust system to vent heat. And, aluminum screen being about the world's best heat conductor, it will dissipate heat from any contact with mufflers, etc...

Is there any guidance on what size screen to use .. I would like to make heavy duty formed pan from heavier screen but dont know about the size of the openings .. bigger holes in the heavier screen than in flimsy window screen. Are we shooting for some kind of ratio of opening to wire like 60% or something?

Don

[edbso]

Hit the screen with a spray for rubber body undercoating to seal all holes. You might want to leave some openings around hot mufflers, cats and pipes.

I used standard window screening, aluminum not plastic.

[dmac257]

Originally Posted by edbso

Hit the screen with a spray for rubber body undercoating to seal all holes. You might want to leave some openings around hot mufflers, cats and pipes.

I used standard window screening, aluminum not plastic.

Otto had said "Why paint it? The naked screen should be adequate to smooth the air flow, while allowing the exhaust system to vent heat. And, aluminum screen being about the world's best heat conductor, it will dissipate heat from any contact with mufflers, etc..." so I was asking if there was any literature or such for what size openings because I want to make a belly pan out of heavier screen than standard window screen. The hardware store has screen that looks like it is made of wire that is three times the thickness of window screen with slightly larger openings. As this would be stiffer, I think this would resist damage a little better, but will it work for smoothing air flow?

Don

[edbso]

I am not an expert here.
There is extremely strong stainless steel screening available if you are interested in strength. I believe that it has standard hole size.

[edbso]

Final post:

Sold the MATRIX.

The general public was not interested in a modified car and I had to remove everything before I could sell it.

Replaced with a Mercedes Turbo Diesel.

Thanks to all for their help.

[eco_generator]

Originally Posted by edbso

The general public was not interested in a modified car and I had to remove everything before I could sell it.

Replaced with a Mercedes Turbo Diesel.

Very common, usually much better to take off mods and sell them separately.

[conehead433]

I saw some plastic 4 x 8 wall panels at Lowe's that were only about $16. It's pretty thin stuff and pretty flexible. I thought it might make a good belly pan material for my 1999 Chevrolet Metro. Anyone have any experience with this or other similar materials?

[aerohead]

Originally Posted by conehead433

I saw some plastic 4 x 8 wall panels at Lowe's that were only about $16. It's pretty thin stuff and pretty flexible. I thought it might make a good belly pan material for my 1999 Chevrolet Metro. Anyone have any experience with this or other similar materials?

The material would make great 'skin' but would require close grouping of its support structure between spans.The coroplast might offer the 'smoothness' and rigidity you need with gravity acting on it constantly, and allow further distance between support structures ( lighter weight/simpler fabrication ).