Air flow.

When you drive a car do you notice that there is a fan in the front? This is because without that fan air can successfully move around the vehicle without lifting it off the ground. As you may notice Volvo's do tend to have a higher fan this is because if someone were to fall in the road you wouldn't get caught under the car, not because of the air flow.

Turbulent:

This is somewhat of a crazy air flow, which means there is air flowing in ALL DIRECTIONS. You may notice that when you are in an airplane that it sometimes becomes bumpy, this is because the air surrounding the air craft is going in all directions.

Linear:

The air moves in one steady direction.

Cars tend to have both turbulent and linear wind patterns this means that in general the top layer of air the flies over top the car is linear and that the air flow near the bottom of the car is turbulent.

Any questions about the topics? Then consult your notes, myself, friends, or Mr. Foster. If you are still confused refer to the Internet.