Turbine Specific Speed — Physical Meaning The specific speed of a turbine is defined as the speed of an imaginary turbine, geometrically similar to the given turbine, which operates under unit head and what output condition?

Introduction:
Specific speed allows turbines of different sizes and heads to be compared on a common basis. It specifies the speed at which a geometrically similar turbine would run to produce a standard output at a standard head, guiding type selection and speed matching to generators.

Given Data / Assumptions:

• Unit head means H = 1 m (in conventional metric usage).
• Output condition used in the definition is unit power.
• Geometric and dynamic similarity are implied.

Concept / Approach:
The accepted definition for turbines is: “speed of an imaginary geometrically similar turbine which develops unit power under unit head.” From similarity, the common formula is Ns = N * sqrt(P) / H^(5/4) (rpm-based), consistent with the physical definition stated.

Step-by-Step Solution:
Fix H = 1 and P = 1 (unit values).Determine the rotational speed N that a similar turbine would need at those unit conditions.That N is, by definition, the specific speed of the actual turbine.

Verification / Alternative check:
Type ranges: Pelton has low Ns, Francis medium, Kaplan high; the computed Ns places a site within these families.

Why Other Options Are Wrong:
unit discharge phrases: apply to pump specific speed, not turbine definition.unit speed: not part of the turbine Ns definition.

Common Pitfalls:
Mixing turbine and pump specific speed formulas; turbines use power, pumps use discharge.

Final Answer:
develops unit power under unit head