Osborne Reynolds FRS (23 August 1842 – 21 February 1912) was an Irish-born[1][2][3] British[4] innovator in the understanding of fluid dynamics.

Separately, his studies of heat transfer between solids and fluids brought improvements in boiler and condenser design.

[5] His father, Reverend Osborne Reynolds, was a Fellow of Queens' College, Cambridge who worked as a school headmaster and clergyman, but was also a very able mathematician with a keen interest in mechanics.

The father took out a number of patents for improvements to agricultural equipment, and the son credits him with being his chief teacher as a boy.

This professorship had been newly created and financed by a group of manufacturing industrialists in the Manchester area, and they also had a leading role in selecting the 25–year–old Reynolds to fill the position.

Reynolds also proposed what is now known as Reynolds-averaging of turbulent flows, where quantities such as velocity are expressed as the sum of mean and fluctuating components.

The ability to make a small scale model of a ship, and extract useful predictive data with respect to a full size ship, depends directly on the experimentalist applying Reynolds' turbulence principles to friction drag computations, along with a proper application of William Froude's theories of gravity wave energy and propagation.

Areas covered besides fluid dynamics included thermodynamics, kinetic theory of gases, condensation of steam, screw-propeller-type ship propulsion, turbine-type ship propulsion, hydraulic brakes, hydrodynamic lubrication,[10] and laboratory apparatus for better measurement of Joule's mechanical equivalent of heat.