Quote:
Originally Posted by Viturro
........ i don't think that there's a low pressure on the back of the wheel... so why it should have less drag?
|
The faster moving air just above the wheel will have the tendency to draw higher pressure air to it. It literally sucks up the surrounding air.
Another example: I have a roof wing on my pick up truck. The small gap between the roof and the wing accelerates air downward at a 45 degree angle (I beveled the edge). This air curtain of sorts draws in the higher pressure air above it, allowing my rear spoiler to be more effective as the air moves along the top of the bed cover.
Higher velocity air = low pressure
Lower velocity air = higher pressure
By forcing air though a narrowing opening the air is accelerated, thereby increasing velocity and lowering the air pressure.
The higher pressure surrounding air will rush to fill the void and gets sucked in and follows.