Found some extra links on the BMW version
BMW Drops the Goods on the 2011 1-Series M Coupe (With Photos!) | The Smoking Tire
BMW EfficientDynamics
BMW EfficientDynamics : Aerodynamics
From the first link:
Quote:
Air Curtains.
Consistency between form and function is crucial to engineers at BMW M, who seek perfect balance of various aerodynamic factors in the wind tunnel. As a result, the 1 Series M Coupe has been equipped with BMW’s latest aerodynamic innovation. Air curtains, used here for the first time in a BMW production vehicle, improve air flow around the wheel arches with the benefit of significantly reduced turbulence.
This innovative aerodynamic feature consists of openings in the outer section of the lower front fascia that route high-pressure air through ducts at each front corner. The ducts are approximately 10 x 3 centimeters wide and are designed to channel air to openings at the front of each wheel arch, where it is discharged through a very narrow opening at high speed. The escaping air stream covers the side of the front wheels like a curtain, thereby reducing aerodynamically unfavorable turbulence around the rotating wheels.
This feature has a key role to play in the development of future aerodynamic innovations. An example of the air curtain principle was first presented in the concept study BMW Vision EfficientDynamics at the International Motor Show (IAA) in Frankfurt in 2009, and the developers of the BMW 1 Series M Coupe took on the pioneering task of applying this element to a production vehicle. To do so, they utilized the unique capabilities of the new full-scale “rolling road” Aerolab wind tunnel at the BMW Group’s new Aerodynamic Testing Center.
|
This gives a few nice details, in particular:
* The intake size in this case is only ~ 30 square cm, which is tiny by "ricer scoop" standards.
* They're using the venturi effect to accelerate the air to produce the air curtain, which makes sense.
An air curtain is a well-established phenomenon. Lateral forces have a smaller effect on the *direction* of a faster air stream than if it were moving slower - the fast moving air creates a 'virtual surface' which reduces cross-flow.
As noted previously in this thread, the BMW implementation only seems to cover the centre section of the tyre - perhaps this is because that's where the edge of the tyre is perpendicular to the airflow? One could speculate that the BMW engineers found that creating an air curtain over the whole height of the wheelhouse required too large a scoop, and chose the height with the best tradeoff between scoop drag and air curtain effect...