At what Reynolds number is flow typically considered turbulent in a vessel?

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

Answer: (C)

Reynolds number shows the balance between inertial forces that promote mixing and viscous forces that smooth out motion. In many vessel and pipe flows, that balance crosses into turbulence once Re reaches about 2000. Below this value, disturbances tend to be damped and the flow stays laminar; above it, disturbances can grow and the flow becomes unstable and chaotic, i.e., turbulent. The exact switch can shift with roughness and disturbances, so there’s a transitional range, but using around two thousand as the threshold is the standard practical cue for when turbulence starts to appear. That’s why the best choice is the value near 2000.