Difficulty: Easy
Correct Answer: Lower critical velocity
Explanation:
Introduction / Context:
Reynolds number Re characterizes the ratio of inertial to viscous forces in a flow. In internal flows through pipes, specific Re thresholds indicate transitions between laminar, transitional, and turbulent regimes. The velocity associated with Re ≈ 2000 has a special name.
Given Data / Assumptions:
Concept / Approach:
The velocity at which laminar flow tends to become unstable is called the lower critical velocity (corresponding to Re ≈ 2000). A higher threshold, sometimes termed higher critical Re (≈ 4000), marks where turbulence is fully sustained.
Step-by-Step Solution:
Verification / Alternative check:
Experimental pipe-flow charts and Moody diagrams demarcate laminar, transitional, and turbulent zones near these Re values.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing Re thresholds with compressibility criteria; they are independent nondimensional groups.
Final Answer:
Lower critical velocity
Discussion & Comments