Turbulent Flow MCQ with answer and solution

Concept

Reynolds Stress in Turbulent Flow

Formula

τ = -ρu'v'

Step-by-step solution

1. Identify the formula for Reynolds stress in turbulent flow: τ = -ρ (u' v'). 2. Observe that u' and v' represent the fluctuating components of velocity in the x and y directions. 3. Match this relationship to select Option C (Fluctuating components of velocity).

Explanation

In a turbulent flow, fluid particles move chaotically with rapid, random fluctuations in velocity. Reynolds stresses represent the apparent additional shear stresses caused by these continuous, fluctuating velocity components transferring momentum across the flow.

Shortcut

Remember: Turbulent flow means chaos and fluctuations, so Reynolds stress is always associated with fluctuating components of velocity (u' and v').

Common mistake

Students often confuse Reynolds stress with viscous shear stresses (Option D) or assume it is driven directly by mean flow velocities (Option A), forgetting that Reynolds stresses arise specifically from momentum transport by turbulent velocity fluctuations.