What is the difference between a blade and a vane in a turbine? When constructing velocity triangles, there are two angles at inlet and outlet (α & θ, β & φ), respectively. My textbook defines α & β as blade angles and θ & φ as vane angles. What is the difference between them?
I don't understand why the textbook uses the terms "blade angle" and "vane angle" here, but the point is that you need to consider two sets of angles.
One set ($\alpha$ and $\beta$) describe the fluid flow direction relative to the fixed turbine structure. The other set ($\theta$ and $\phi$) describe the flow direction relative to the rotating blades. The vectors $u1$ and $u2$ in the velocity triangles come from the velocity $u$ of the blade as it rotates.