Reducing rotor speed in impulse turbines Which compounding method(s) are employed to reduce the excessively high rotor speed that would result from a single-stage impulse expansion?

Introduction / Context:
A single large pressure drop in impulse turbines creates very high jet velocities and would require unrealistically high rotor speeds for optimum energy extraction. Compounding methods split the work extraction to bring practical speeds while maintaining efficiency.

Given Data / Assumptions:

• Impulse expansion of steam through nozzles produces high absolute velocities.
• Blade tip speed for best efficiency is a fraction of jet speed.
• Mechanical limits and generator synchronization restrict allowable rotor speeds.

Concept / Approach:

Velocity compounding (Curtis) converts the full pressure drop to a single high-velocity jet but extracts energy over multiple moving rows, lowering the required rotor speed. Pressure compounding (Rateau) divides the pressure drop across multiple nozzle-rotor stages, reducing jet velocity each time. Pressure-velocity compounding uses a hybrid approach, first splitting pressure, then using velocity compounding within each partial drop to further moderate speed. All three reduce rotor speed relative to a single-stage impulse arrangement.

Step-by-Step Solution:

Verification / Alternative check:

Comparing blade-speed ratios and power curves across compounded arrangements shows reduced optimal rotor speeds while maintaining acceptable efficiency bands.

Why Other Options Are Wrong:

Reaction staging is a different principle (pressure drop in moving blades) and is not required to solve an impulse rotor speed limitation.

Common Pitfalls:

Assuming one method is universally superior; selection depends on pressure ratio, power, and manufacturability.

Final Answer:

all of these