Fluid mechanics – identifying flow regime where viscous forces dominate over inertia Choose the correct option that best describes such a flow.

Introduction:
In fluid mechanics, flows are classified by the relative importance of viscous forces compared to inertia forces. This question tests whether you can identify the flow regime in which viscous effects dominate the motion, smoothing out velocity differences and preventing mixing across adjacent layers.

Given Data / Assumptions:

• Single-phase, Newtonian fluid is considered.
• Internal flow in a conduit is the typical mental model, but the concept holds broadly.
• Low Reynolds number conditions are implied (Re much less than the critical value).

Concept / Approach:
Reynolds number Re = (rho * V * L) / mu compares inertia forces (rho * V^2 * L^2 scale) to viscous forces (mu * V * L scale). When Re is small, viscous forces dominate inertia. In such conditions, fluid moves in smooth, orderly layers with minimal mixing—this is laminar flow. When Re is large, inertia overwhelms viscosity, and turbulence can occur.

Step-by-Step Solution:

Verification / Alternative check:
A hallmark of laminar flow is a predictable velocity distribution (e.g., parabolic in fully developed pipe flow) and the absence of eddies; pressure drop follows linear relations with flow rate in the Hagen–Poiseuille regime, reinforcing viscous dominance.

Why Other Options Are Wrong:

• Steady flow: time-invariant, not about viscous vs inertia dominance.
• Unsteady flow: time-varying; again not defining force balance.
• Turbulent flow: inertia dominates; strong mixing and eddies.
• Uniform flow: velocity same across a section; not guaranteed by viscous dominance.

Common Pitfalls:
Confusing “steady” with “laminar” or assuming low velocity automatically means steadiness. The key discriminator is the Reynolds number and the viscous–inertia balance, not whether the flow changes with time.

Final Answer:
laminar flow