Stage count comparison:\nFor the same overall pressure ratio and output, a pressure-compounded impulse turbine requires ________ number of stages compared with a velocity-compounded (Curtis) turbine.

Introduction / Context:
Impulse turbines can be compounded by dividing the total expansion by pressure (Rateau compounding) or by velocity (Curtis compounding). The compounding method influences stage count, blade loading, and efficiency. Knowing which arrangement needs more stages helps in conceptual design and cost estimation.

Given Data / Assumptions:

• Comparable total pressure drop and desired output.
• Acceptable blade tip speeds and nozzle angles.
• Classical idealizations for compounding.

Concept / Approach:
In pressure compounding, the overall pressure drop is split into multiple sequential nozzle–rotor stages, each with modest velocity. This typically requires several stages to share the expansion. In velocity compounding, a single large nozzle drop produces a high jet speed, and multiple moving rows within the same stage (with intervening fixed guides) distribute the velocity change. Consequently, for the same duty, pressure-compounded arrangements generally need more separate stages than velocity-compounded ones.

Step-by-Step Solution:

Verification / Alternative check:
Historical turbine designs (Rateau vs Curtis) exhibit exactly this difference in stage allocation and blade speed constraints.

Why Other Options Are Wrong:

• Same/Less: Contradicts standard compounding practice and design trade-offs.
• Indeterminate: While details vary, the general rule remains robust for comparable duties.

Common Pitfalls:
Confusing “stage” with “row”: velocity compounding places multiple moving rows in a single stage.

Final Answer:
more