Definition of Reynolds number in English:

Reynolds number


  • 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

    • ‘He spoke on boundary layer theory, in particular flows at high Reynolds numbers, in his inaugural lecture in London.’
    • ‘The Reynolds number equation states that turbulent flow is created by higher gas velocity, gas density, and tube radius and lower gas viscosity.’
    • ‘The higher Reynolds number for the tadpole indicates that it is ‘faster and better at overcoming the viscous drag that typically confronts small aquatic organisms,’ the biologists report in Nature.’
    • ‘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.’
    • ‘Small objects have lower Reynolds numbers - a dimensionless quantity proportional to the ratio of the product of the size and flow speed to viscosity.’


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


Reynolds number