Wind Chart/Diagram, How's It Look? Options

[Bigmeanbulldog55]

I was driving back to college from home, and it was raining out. I noticed that the back glass kept dry even in the heavey rain. This just made me curious to see a wind chart for the celica. It's a hachback with a wing. Any have this? And I was also wondering how functional this wing really is? Any know? Thanks.

[orvillescelica]

spoilers and wings are two different beasts. A wing creates downforce and are thus useless on fwd cars like ours. But a spoiler is meant to distrubt the airflow coming off the back of the car. It effectivly decreases the coefficent of drag by as much as .05 . Im not in the car areodynamics biz, so i dont know exactly the dynamics that are invovled but i have two theories by just thinking about it.

1) Airflow coming off the roof that is slowed from friction with the car (an area of airflow known as the 'boundary layer') seperates as it decends from the roof down the hatch. This flow becomes turbulent. But the seperation is low enough that the turbulent boundary layer reattaches on the spoiler and the properly flows off the back. This keeps the effective flow above the boundary layer streamline with the end of the car, and thus a lower coefficent of drag.

2) The spoiler controls the angle of the flow coming off the end of the car, creating a more exagerated vortex that is known as the 'Kutta Condition.' Since this vortex is bigger and has a greater moment, the fixed vortex at the front of the car must also be bigger to balance it out. This pushes the stagnation point (the front o fthe car where the forward coming air hits) lower, and thus the air must 'swoop' upward to go over the hood. 'swooping' creates a negative pressure area at the front of the car, creating a force the counteracts drag. Thus the overall coefficent of drag is decreased.

Assuming only one of my theories are true. The reason why rain does not hit the back of window as much can be explained by my first theory. Since the effective flow follows the boundary layer, and it is dettached at that point. Any rain particles at low velocity will be swept up in the effective flow at higher velocities. So the rain is swept away by the flow and does not hit your car.

of course, like i said, im not in the car aerodynamics business. So this is all speculation. The aerodynamics i deal with, our cars would have to travel at Mach 6.