Reaction turbine working principle

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Let me start this question with a quote:

"In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor."

So: "... reaction force produced as the steam accelerates through the nozzles formed by the rotor," but... "with steam decelerating through the rotor."

What? As i understand it, increasing the velocity of the fluid requires a force to be acted on a fluid, therefore, fluid exerts an equal force and opposite force to drive the rotor.

Therefore, If the reaction turbine acts as a lawn sprinkler, shouldn't velocity in the rotor increase? But somehow, viewing the diagrams I noticed the velocity drops across the rotor blades. If the rotors acts as a converging nozzle then yes, i understand why pressure drops, but i can't understand why velocity drops.

Thanks!
 

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  • #2
jack action
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The steam velocity relative to the blades is increasing, but because the rotor blades are moving in the opposite direction, it slows down the absolute steam velocity.

In the following image, w are the velocities relative to the rotor blades, c are the absolute velocities and u is the velocity of the blades. w3 > w2, but c3 < c2.

Velocity_triangle_for_an_axial_turbine_stage.jpg
 

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