Velocity diagram for a rotating blade

[princejan7]

Homework Statement

http://postimg.org/image/5o9kcuj57/
I do not understand what the vectors W and V represent

Homework Equations

The Attempt at a Solution

I know U is the tip speed velocity but I don't know about the other two

 

[haruspex]

It's hard to be sure because the angles alpha and beta are not shown in the upper diagram.
At a guess, beta is the angle the blade makes to the inner hub. W could be a velocity vector relative to the blade, e.g. representing a flow of fluid along the blade surface. V would then be the velocity vector relative to the ground.