 # 1851

## The book of science

Tom Sharp

 George Gabriel Stokes fluid dynamics

## Reynolds number

• 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.

## Reynolds things

• 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 Navier–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.