Osborne Reynolds and the Reynolds Number

In Chapter 1 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I discuss the Reynolds Number.

The importance of turbulence is determined by a dimensionless parameter called the Reynolds number N_R. It is defined by 

N_R = L V ρ / η ,              (1.67)

where L is a length characteristic of the problem, V a velocity characteristic of the problem, ρ the density of the fluid, and η the viscosity of the fluid. When N_R is greater than a few thousand, turbulence usually occurs.

The Reynolds number is named after the British engineer Osborne Reynolds. I wanted to learn more about Reynolds, so I got out my copy of Asimov’s Biographical Encyclopedia of Science & Technology (second revised edition). Guess what? There’s no entry for Reynolds! Over 1500 scientists have entries, and I would have thought that Reynolds would be in the top tenth of a percent so I was surprised. I guess I’ll have to write Reynolds’s entry myself. (The numbers in brackets in the text below refer to Asimov’s numbering system in his encyclopedia.) 

Osborne Reynolds

[758½ ] REYNOLDS, Osborne 

              British engineer      

              Born: Belfast, Ireland, August 23, 1842 

              Died: Watchet, England, February 21, 1912

Reynolds was born in Ireland, but moved to England when he was young. His father, the Reverend Osborne Reynolds, was interested in mathematics and mechanics, and was young Osborne’s main teacher. In this teenage years, Reynolds became interested in the practical aspects of fluid dynamics when working as an apprentice for a shipbuilder. He attended Queen’s College at Cambridge University, where he studied math and in 1867 was the seventh wrangler in the mathematical tripos exam. After graduation, he spent a year in London as an engineer working on the municipal water system (which was a big deal in 19th century London; see my blog post about The Great Stink).

Reynolds spent most of his career as an Engineering Professor at Owens College (now the University of Manchester). There, in 1883, he wrote his most famous paper: “An Experimental Investigation of the Circumstances which Determine Whether the Motion of Water Shall be Direct or Sinuous, and the Law of Resistance in Parallel Channels,” published in the Philosophical Transactions of the Royal Society. The article described his classic experiment in which he introduced a jet of dye into water flowing in a pipe, and examined its transition from smooth (laminar) flow to complex and chaotic (turbulent) flow as the speed of the flow changed. His paper was reviewed for the journal by two referees who were giants of Victorian science: Sir George Stokes [618] and Lord Rayleigh [760]. This paper also analyzed the Reynolds number. The concept of the Reynolds number had been proposed decades earlier by Stokes. Reynolds, of course, didn’t himself call it the Reynolds number. That name was introduced in 1908 by German physicist Arnold Sommerfeld [976].

Besides fluid dynamics and turbulence, Reynolds had other interests, such as lubrication theory (tribology) and shipbuilding. He also studied the kinetic theory of gases, a interest that overlapped with work of the great Victorian physicist James Maxwell [692]. The hydrodynamicist Horace Lamb noted that Reynolds was a generous mentor for research students. His most famous student was JJ Thomson [869], the discoverer of the electron, who worked with Reynolds as an undergraduate.

Reynolds was elected a Fellow of the Royal Society in 1877. In 1888 Stokes, then President of the Royal Society, presented Reynolds with the Royal Medal “for his investigations in mathematical and experimental physics, and on the application of scientific theory to engineering.”

Reynolds retired in 1905 after his health began to fail, and died in 1912. 

Exploring the Reynolds Number: Unveiling Fluid Dynamics

 https://www.youtube.com/watch?v=9BNmV99wCZ4 

Understanding Laminar and Turbulent Flow

 https://www.youtube.com/watch?v=9A-uUG0WR0w&t=738s