Reynolds number & flow regime

modified2026-07-21statusfinished

Classifies laminar vs. turbulent pipe flow from the ratio of inertial to viscous forces.

[3.1] Governing equation

$$Re=\frac{\rho v D}{\mu}=\frac{vD}{\nu}$$

Critical values for circular pipes: laminar Re < 2300, transitional 2300–4000, turbulent Re > 4000.

FIG. 01 — Reynolds' dye trace: parallel streamlines vs. chaotic eddies

Density ρ (kg/m³) Velocity v (m/s) Diameter D (m) Dynamic viscosity μ (Pa·s)

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