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Reynolds number Line breaks: Rey|nolds num¦ber
Pronunciation: /ˈrɛn(ə)ldz/

Entry from British & World English dictionary

Definition of Reynolds number in English:


A dimensionless number used in fluid mechanics to indicate whether fluid flow past a body or in a duct is steady or turbulent.
  • This is evaluated as ρυd/μ, where d is a diameter or other characteristic length of the system, υ is a typical speed, ρ is the fluid density, and μ is the viscosity of the fluid. The magnetic Reynolds number is an analogous number used in the description of the dynamic behaviour of a magnetized plasma
Example sentences
  • Small objects have lower Reynolds numbers - a dimensionless quantity proportional to the ratio of the product of the size and flow speed to viscosity.
  • He spoke on boundary layer theory, in particular flows at high Reynolds numbers, in his inaugural lecture in London.
  • For the purpose of biological fluid dynamics, scale is represented by the dimensionless Reynolds number, a ratio that reflects the influence of inertial relative to viscous forces.


Early 20th century: named after Osborne Reynolds (1842–1912), English physicist.

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