The Reynolds number was derived in 1883 by "the British physicist and engineer Osborne Reynolds," according to The Internet Encyclopedia of Science. The equation for determining a Reynolds number (Re = pVD/viscosity) means fluid or air density multiplied by velocity, multiplied by the diameter of a pipe, and then divided by viscosity.
Reynolds numbers help to determine the motion of fluid. A Reynolds number determines if air or fluid is "either laminar (in smooth layers) or turbulent (rough)," according to The Internet Encyclopedia of Science.
The Reynolds number provides pilots with a tool when attempting to control turbulence, especially in a passenger aircraft. A pilot may change the speed of an aircraft based upon a Reynold's number.