What does it mean when someone says that air is attached to a wheel?
First thing we’ll talk about is a yaw angle. If you think about a wheel on a bicycle, and the wind is coming directly at you, that means you are experiencing zero degrees of yaw, and in that case, people say that the air is attached to the wheel.
If you increase that yaw angle by turning it, the wind hits the wheel at an angle, and the wheel is detached.
With water as an example, you can see that attached means the water holds to the rim at all times. This is attached. Detached means the water is not attached to the surface. This same logic applies with air.