How to Calculate Reynolds Number
What is Reynolds Number?
Reynolds number predicts flow regime: laminar (smooth, orderly) or turbulent (chaotic, mixing). It's dimensionless and crucial for fluid mechanics analysis.
Formula
The calculator applies Re = (ρ × v × L) / η
- Re
- (ρ × v × L) / η — (ρ × v × L) / η
- L
- L value — Variable used in the calculation
Step-by-Step Guide
- 1Enter fluid density, velocity, characteristic length, and dynamic viscosity
- 2The calculator applies Re = (ρ × v × L) / η
- 3Results classify flow and predict behavior
Worked Examples
Input
ρ = 1000 kg/m³, v = 0.1 m/s, L = 0.01 m (water in small pipe), η = 0.001 Pa·s
Result
Re = 1000 (laminar)
Smooth, predictable flow
Common Mistakes to Avoid
- ✕Confusing characteristic length (diameter for pipes, chord for airfoils)
- ✕Using kinematic instead of dynamic viscosity
Frequently Asked Questions
What Reynolds numbers indicate turbulence?
Re < 2300 is laminar, 2300-4000 is transitional, Re > 4000 is turbulent in pipes.
Does Reynolds number apply to all fluids?
Yes, it's dimensionless; the same Re value predicts similar flow behavior regardless of fluid type.
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