Velocity Compounding (Curtis) – Where Does the Expansion Occur? State whether, in a velocity-compounded impulse turbine stage, the steam expansion (pressure drop) takes place entirely in a nozzle or set of nozzles while the moving blade rows operate at essentially constant pressure.

Introduction / Context:
Velocity compounding (Curtis staging) is a classic method to extract work from a very high-velocity jet without requiring impractically high rotor-tip speeds. Clarifying where the pressure drop occurs distinguishes Curtis stages from pressure-compounded (Rateau) arrangements and from reaction stages.

Given Data / Assumptions:

• Impulse principle: pressure drop localized in stationary nozzles.
• Multiple rotor rows with intermediate redirecting fixed guide blades at near-constant pressure.
• Overall pressure drop for the Curtis stage produced by the nozzle set feeding the first rotor.

Concept / Approach:

In a velocity-compounded stage, the steam expands (experiences its pressure drop) in a single nozzle set (or grouped sets), emerging at high velocity. The kinetic energy is then extracted over multiple rotor rows separated by fixed guide blades that merely redirect the flow at approximately constant static pressure. No further intentional expansion occurs in the rotor passages, distinguishing Curtis from reaction designs. Thus, within the Curtis stage envelope, expansion is confined to the nozzles.

Step-by-Step Solution:

Verification / Alternative check:

Textbook pressure/velocity diagrams across a Curtis stage show a single pressure drop across the nozzle, with flat pressure profiles across rotor and guide rows, while velocity steps down over successive rotors.

Why Other Options Are Wrong:

Reaction stages deliberately create pressure drops in rotors; Rateau (pressure compounding) divides pressure drops among multiple nozzle groups between single rotors, not within one velocity-compounded stage.

Common Pitfalls:

Confusing multi-stage turbines (many Curtis stages in series) with the internal distribution within a single Curtis stage; the truth here concerns the single-stage compounding principle.

Final Answer:

True