1. What is Reynolds Number?

The Reynolds number (Re) is a dimensionless quantity used to predict flow patterns in different fluid flow situations. It compares inertial forces to viscous forces and helps determine whether flow will be laminar or turbulent.

2. How Does the Calculator Work?

The calculator uses the Reynolds number equation:

Where:

• \( \rho \) — Density of the fluid (kg/m³)
• \( v \) — Velocity of the fluid (m/s)
• \( D \) — Characteristic length or diameter (m)
• \( \mu \) — Dynamic viscosity of the fluid (Pa·s)

Explanation: The equation shows the ratio of inertial forces (ρvD) to viscous forces (μ) in the fluid flow.

3. Importance of Reynolds Number

Details: Reynolds number is crucial in fluid mechanics for predicting flow regimes:

• Re < 2300: Laminar flow
• 2300 ≤ Re ≤ 4000: Transitional flow
• Re > 4000: Turbulent flow

4. Using the Calculator

Tips: Enter all values in consistent SI units. Density and viscosity values can be found in fluid property tables for common substances like water, air, oils, etc.

5. Frequently Asked Questions (FAQ)

Q1: What is characteristic length (D)?
A: For pipes, it's the inner diameter. For other geometries, it's typically the length scale relevant to the flow (e.g., chord length for airfoils).

Q2: How does temperature affect Reynolds number?
A: Temperature affects viscosity and density, which both influence Re. For liquids, viscosity decreases with temperature, potentially increasing Re.

Q3: What's the difference between dynamic and kinematic viscosity?
A: Kinematic viscosity (ν) is dynamic viscosity (μ) divided by density (ρ). Reynolds number can also be expressed as Re = vD/ν.

Q4: Can Reynolds number be used for non-circular pipes?
A: Yes, but use hydraulic diameter (4 × cross-sectional area / wetted perimeter) as the characteristic length.

Q5: What are typical Re values in engineering applications?
A: Blood flow in arteries (~100-1000), water in pipes (~10³-10⁶), air over aircraft wings (~10⁶-10⁸).