Meaning of Reynolds number in English:

Reynolds number

Pronunciation /ˈrɛn(ə)ldz/


  • 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

    ‘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.’
    • ‘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.’


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