The wind speed above is the relative wind speed, relative to the wind speed of the blades. It is the combination of the wind speed in the vertical plane of rotation and the speed of blade rotation.
You can imagine that if the blade does not move, it will be vertical. If it rotates, it will still have a wind speed. Once combined, it will be in this direction. In fact, it is not parallel to the inclined plane. There is also an angle called the angle of attack, which will affect the power of power generation. Haha, I'm sorry, this is quite complicated and I can't figure it all out.