How does the rotor of a steam turbine convert steam energy into motion?

The rotor of a steam turbine converts steam energy into motion by utilizing the principle that a force is exerted when a mass of steam undergoes a change in velocity. The rotor, which is mounted on a shaft and enclosed in a casing, features attached vanes or blades that capture this force in the tangential direction, causing the rotor to turn.123

This conversion process generally occurs through two primary blading designs:

• Impulse blading: Stationary nozzles accelerate the steam, increasing its velocity and kinetic energy. This high-velocity steam is directed against the rotor blades, where the kinetic energy is extracted as the steam changes direction.1
• Reaction blading: Both the stationary stator passages and the moving rotor passages contribute to the expansion of steam. As the steam expands and its pressure drops, it accelerates through the rotor passages, exerting a net force that turns the wheel.1

Ultimately, these blades are aerodynamically shaped to efficiently transform the thermal energy of the steam into the rotary motion of the shaft.13