| My panties were tight. A diffuser is a very simple thing. But the one thing it is not is a wing in the traditional sense. The ideal diffuser for your car, or any car will be an upward arcing surface that starts at 0% to the floor/ground and ends around 17-19 degrees. Final degrees of the terminating point is determined by maximum velocity, but the general rule of thumb for a 150mph car is 17-19. Anything above this and the flow seperate creating drag.
By the look of your design, it is a flat surface that stays at 12 to 15 degrees. Secondly, you want to fence off as much of the wheel as possible. Your's is close. But the additional element(s) behind the tire will do very little for you other then add weight. You are better off building a boat hull behind the rear wheel to help force the dirty tire air away from the rear of car. Verticle stakes that at in line with the car (0 degrees on center upto to 3 degrees out as you go outboard) is the general rule of thumb again. Also, haveing deep strakes that create vortices off the tips is ideal, ESPECIALLY closes to the tires.
As FuerGrissa said, you want to take the clean air that you have under the car and get it as high as you can, and to fill the air pocket behind the car. The cleaner the air here, the greater efficiency your rear spoiler/wing will have. As far as the double element diffuser, there are many many articles on this in RaceCar Engineering, Race Tech, and Bernouilli that go into how one cancels the other.
In F1, they were using a double/triple element diffuser, but the source air for the second/third diffuser was different then the first. Their intent was to pump as much air behind the center part of the car as they can to reduce drag and help push air up and under the rear wing to increase downforce. F1 cars however have significantly different body shapes then our cars. For use to make use of a proper Dual element design, I'd invision that you would have three inlets to the diffuser.
The second element diffuser (closest to the ground) would be a flat floor that arcs up into a standard diffuser.
The upper element would be fed by two large NACA style ducts out board or forward of the flat floor diffuser. You can then pump air into the upper diffuser area to decrease drag and help increase rear wing performance. I firmly believe that a very simple diffuser design, that is designed around the exhaust, will yield greater results in both downforce and drag, then an overly complicated one. The ideal diffuser also will 'see' as much road surface as possible, because that rolling air pocket generated by the road surface is what fills the rear of the car with. IMHO.
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nixit. queen of all assholes.
Petz #3
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16:53:35 03/19/11
