Mclaren has on their webpage a section that describes the fundamentals of different parts of the car. The subject changes every race, and this week they have a very interesting article on the aerodynamic development of the car, plus an article on brakeducts. I suggest you check it out.
http://www.mclaren.com
there is a links section on the right, and there it is, called "the brakeduct" and "there's something in the air"
They have mclaren engineers explain the things. They have had some very interesting articles there.