Turbulent flow in vessels is most likely to occur when Reynolds number exceeds about which value?

• A. 1000
• B. 3000
• C. 2000
• D. 1500

Answer: (C)

Reynolds number compares inertial forces to viscous forces in a flow. When inertia dominates (higher Re), disturbances aren’t quickly damped and the flow tends to become chaotic and turbulent; when viscous forces dominate (lower Re), the flow stays smooth and laminar. For flow in vessels and pipes, the transition from laminar to turbulent is typically observed around a Reynolds number of about two thousand. So when Re exceeds roughly two thousand, turbulent flow becomes much more likely. The lower values stay laminar, while higher values can be turbulent, but two thousand is the standard practical cue for the onset of turbulence. Keep in mind the exact boundary can shift with surface roughness and disturbances, but two thousand is a common guideline.