Question

Reynolds stresses arise due to:

• A. Laminar sublayer
• B. Density variation
• C. Mean flow gradients
• D. Turbulent fluctuations

Hint:

In turbulent flow, the fluctuating velocities of the fluid lead to Reynolds stresses, which are a key factor in determining the resistance to flow and energy dissipation.

Answer 1

The Correct Option is D

Reynolds stresses arise due to the fluctuating velocities in turbulent flows. These stresses represent the momentum transfer due to the turbulent eddies that occur in the flow.
In turbulent flow, the velocity of the fluid particles fluctuates in both time and space. These fluctuations lead to stresses, known as Reynolds stresses, that resist the flow and contribute to the overall resistance in the fluid. These stresses can be mathematically expressed in terms of the turbulent velocity components and their fluctuations.
The correct cause for Reynolds stresses is turbulent fluctuations. These fluctuations in velocity create turbulent eddies which cause the momentum exchange in the fluid, leading to the Reynolds stresses.
- Laminar sublayer is a region in turbulent flow where the flow is laminar and does not contribute to turbulent stresses.
- Density variation does not directly lead to Reynolds stresses but may influence the flow characteristics.
- Mean flow gradients affect the velocity profile but do not directly create Reynolds stresses; they are related to the overall flow behavior.
Thus, Reynolds stresses arise due to turbulent fluctuations.