A fluid is flowing through a tube. To undergo transition from laminar to turbulent flow its velocity must be:
- A. Slightly less than critical velocity
- B. Equal to critical velocity
- C. Greater than critical velocity
- D. Increasing gradually but less than critical velocity
Explanation
Below the critical velocity the flow stays in orderly layers, and only once that threshold is passed does the motion break up into eddies and become turbulent. The critical velocity is set by the Reynolds number, which combines density, viscosity, speed and pipe diameter. Turbulent flow dissipates far more energy, which matters in pipelines and in blood vessels alike.