Question

Turbulent flow is generally observed when Reynolds number is:

• A. \(<2000 \)
• B. \(>4000 \)
• C. \(<500 \)
• D. Between 500-1000

Hint:

Reynolds number is crucial for determining the flow regime. When \( Re \) exceeds 4000, flow becomes turbulent, causing chaotic fluid motion.

Answer 1

The Correct Option is B

The Reynolds number (Re) is a dimensionless number used to predict the flow regime in fluid mechanics. It is defined as: \[ Re = \frac{\rho v L}{\mu} {or} Re = \frac{v L}{\nu} \] Where:
- \( \rho \) is the fluid density,
- \( v \) is the velocity of the fluid,
- \( L \) is a characteristic length (such as diameter for pipe flow),
- \( \mu \) is the dynamic viscosity,
- \( \nu \) is the kinematic viscosity.
The flow regime is categorized as follows: - For \( Re<2000 \), the flow is generally laminar, meaning the fluid flows in smooth layers with minimal mixing.
- For \( Re>4000 \), the flow becomes turbulent, characterized by chaotic and irregular fluid motion with eddies and vortices.
- For \( 2000<Re<4000 \), the flow is in the transitional region, where the flow may shift between laminar and turbulent depending on the specific conditions.
Therefore, turbulent flow is generally observed when the Reynolds number is greater than 4000.