Reynolds number

Rey·nolds number

noun \ˈre-n^əldz-\

Definition of REYNOLDS NUMBER

: a number characteristic of the flow of a fluid in a pipe or past an obstruction

Origin of REYNOLDS NUMBER

Osborne Reynolds †1912 English physicist

First Known Use: 1910

Reynolds number

noun    (Concise Encyclopedia)

In fluid mechanics, a number that indicates whether the flow of a fluid (liquid or gas) is absolutely steady (in streamlined, or laminar flow) or on the average steady with small, unsteady changes (in turbulent flow; see turbulence). The Reynolds number, abbreviated N or Re, has no dimensions (see dimensional analysis) and is defined as the size of the flow—as, for example, the diameter of a tube (D) times the average speed of flow (v) times the mass density of the fluid ()—divided by its absolute viscosity (). Osborne Reynolds demonstrated in 1883 that the change from laminar to turbulent flow in a pipe occurs when the value of the Reynolds number exceeds 2,100.