Pipe Flow Transition – Definition of Higher Critical Velocity In internal pipe flow, the higher critical velocity corresponds to the speed (or Reynolds number) above which turbulence is fully established; hence the statement that turbulent flow starts at the higher critical velocity is correct.

Introduction:
Transition from laminar to turbulent flow in pipes is commonly described using two threshold velocities (or Reynolds numbers). This question targets recognition of the role of the higher critical value in initiating sustained turbulence.

Given Data / Assumptions:

• Newtonian fluid in a circular pipe.
• Disturbances and surface roughness within normal ranges.
• Reynolds number Re = (rho * V * D) / mu.

Concept / Approach:

Below the lower critical value the flow is stably laminar. Between the lower and higher critical values, the flow is transitional and sensitive to disturbances. Above the higher critical value, turbulence is fully sustained. Therefore saying “turbulent flow starts” at the higher critical velocity is acceptable in practical engineering usage.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory observations show intermittent turbulence in the range between the critical values; fully turbulent profiles dominate beyond the higher critical threshold.

Why Other Options Are Wrong:

No: Conflicts with standard terminology. Other options impose conditions unrelated to the definition.

Common Pitfalls:

Assuming a single sharp universal value; actual thresholds depend on inlet conditions and roughness.

Final Answer:

Yes