# 1851

## Reynolds number

## The book of science

Tom Sharp

Tom Sharp

George Gabriel Stokes fluid dynamics |

- A property of a flowing gas or liquid,
- the ratio of its inertial and viscous forces
- and proportional to its speed for a given length,
- the Reynolds number helps predict
- the scaling effects and the transition
- of laminar to turbulent flow
- of fluids in pipes,
- of air over airplane wings,
- and of weather conditions.
- A high Reynolds number
- means that inertial forces
- outweigh viscous forces,
- and a low Reynolds number
- means that viscous forces
- outweigh inertial forces.

- Stokes introduced the concept in 1851.
- Osborne Reynolds popularized it in 1883.
- Arnold Sommerfeld named the number in 1908
- to honor Reynold.
- Can a similar story be told
- about the Reynolds transport theorem,
- Reynolds decomposition,
- Reynolds stress,
- Reynolds-averaged Navierâ€“Stokes equations,
- Reynolds dilatancy,
- and the Reynolds operator?

- Your number is not dimensionless.
- Your number is a measure of you.
- Your number brings joy to some,
- and irritates others beyond measure.
- Some think they have your number;
- others know it as a mystery of mysteries.

Osborne Reynolds publicized the work of George Gabriel Stokes by varying the velocity of water in a glass pipe and introducing into it a narrow stream of dyed water to demonstrate the onset of turbulent flow. Reynolds made many contributions to the fields of fluid mechanics, fluid dynamics, and heat transfer as both a scientist and an engineer.

See also in

The book of science:D’Alembert’s paradox—Jean le Rond d’AlembertThermal transpiration—Osborne Reynolds, Martin KnudsenEkman transport—Vagn Walfrid Ekman, Fridtjof NansenBoundary layer—Ludwig PrandtlReadings on wikipedia:

Other readings: