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Osborne Reynolds was born in Belfast in 1842 and moved as a young child to Essex, which is within the borough of Colchester between London and Ipswich in southeastern England. Reynolds’ father could safely be called a “renaissance man.” He was a school headmaster and clergyman who happened to have a gift for mathematics and a keen curiosity about mechanics. Osborne credited his father with teaching him much of what he learned about math and mechanics as a boy.
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When Osborne Reynolds was in his late teens, he spent a year before entering Cambridge University as an apprentice in the workshop of a mechanical engineer near Essex. There he gained hands-on experience in the manufacture of coastal steamers, which were used as service and supply vessels off the eastern coast of Britain. Whether he consciously realized it or not, his work with these steamers gave him a useful appreciation of fluid mechanics.
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At Cambridge, Reynolds studied mathematics, a passion that he likely inherited from his father. On his application for a professorship at Owens College, Reynolds wrote, “From my earliest recollection I have had an irresistible liking for mechanics and the physical laws on which mechanics as a science is based… for the explanation of which I discovered that a knowledge of mathematics was essential.”
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Among engineers, Reynolds is still famous for his studies of fluid flow as it makes the transition from laminar, or smooth, orderly flow to turbulent flow, in which inertial forces cause random eddies and vortices. The Reynolds number, Re, is a concept familiar to mechanical and aerospace engineers everywhere. It is a dimensionless number (meaning there are no units, like feet per second, but a plain number) measuring the ratio of inertial forces to viscous forces. This gives a quantitative measure of the relative importance of inertial and viscous forces in various flow conditions. Laminar flow occurs at low Reynolds numbers, where viscous forces dominate, and turbulent flow occurs at high Reynolds numbers, where inertial forces dominate.
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Another concept essential to the education of mechanical and aerospace engineers is that of time-averaged equations of fluid flow. The so-called Reynolds-averaged Navier-Stokes equations are used with approximations based on flow properties of turbulence to obtain approximate averaged solutions to the Navier-Stokes equations.
The use of Reynolds number in Reynolds Averaged Navier-Stokes equations for turbulent fluid flow greatly simplifies what is an almost impossibly complex task, even for today’s high powered computers. Osborne Reynolds may have died almost 100 years ago, but his mathematical work was fundamental enough that it is still part of the basic education of engineers working on some of the most complex machinery in existence.
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Honors and Legacy
Osborne Reynolds spent his entire career at Owens College, which was renamed University of Manchester in 1880. He was named a Fellow of the Royal Society and awarded the Royal Medal in 1888 which was annually awarded to the “two most important contributions to the advancement of Natural Knowledge, published originally in Her Majesty’s dominions within a period of not more than ten years and not less than one year of the date of the award…”
That his mathematical work is still in use today is a testament to the mathematical and mechanical genius of Osborne Reynolds.
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