Reynolds Number
A dimensionless parameter used in fluid mechanics to help predict flow patterns under different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow; at high Reynolds numbers, turbulence tends to be a predominant flow condition.
The Reynolds number formula is expressed as:
where ρ is density of the fluid (kg/m3); V is velocity of the fluid (m/s); μ is viscosity of fluid (N-s/m2); and L is length or diameter of the fluid (m).
Flow regimes based on the value of Re:
- If Re < 2000, the flow is laminar.
- If Re > 4000, the flow is turbulent.
- If 2000 < Re < 4000, the flow is in transition.
See also Laminar Flow; Transition Flow; Turbulent Flow.