Flow Classification – Time Variation of Discharge A flow in which the quantity of liquid flowing per second (discharge) remains constant with time at a given section is called steady flow.

Introduction:
Fluid flows can vary with time and/or space. This question checks the definition of steady flow, where discharge at a fixed cross section does not change with time, a key assumption in many engineering calculations.

Given Data / Assumptions:

• Single-phase liquid in a conduit or open channel.
• Observation made at a fixed section.
• Flow properties may vary across the section but we consider the section-mean values.

Concept / Approach:

Steady flow means that any property at a point (or section-mean discharge) is constant with time: dQ/dt = 0. This is independent of whether velocity changes along the length (uniform vs non-uniform) and independent of flow regime (laminar vs turbulent).

Step-by-Step Solution:

Verification / Alternative check:

Many pipelines operated at fixed pump settings display nearly constant Q over long intervals, qualifying as steady even though velocity profiles across the section are non-uniform.

Why Other Options Are Wrong:

Streamline: Describes particle paths, not time variation of discharge. Turbulent: Refers to regime, not time variation. Unsteady: Means Q varies with time. Uniform: Means velocity is the same at all sections along the length, which is a spatial criterion.

Common Pitfalls:

Confusing steady/unsteady (time) with uniform/non-uniform (space) and with laminar/turbulent (regime).

Final Answer:

steady