Reynolds' number

Definition: Symbol Re. A dimensionless number used in fluid dynamics to determine the type of flow through a pipe, to design prototypes from small-scale models, etc. It is defined as the ratio of the inertial and viscous forces.

Re = ρDu/μ

where D is a characteristic length (for example, a pipe diameter) , u is the characteristic velocity and μ is the viscosity. The Reynolds' number can be used to discriminate between laminar and turbulent flow, with Re <>3000.

Common Misspellings: Reynold's number