Reynolds Number: Dimensionless Quantity, Ratio, Inertia, Osborne Reynolds, Dimensional Analysis, Similitud, Eddy, Vortex, Rotation

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In fluid mechanics, the Reynolds number Re is a dimensionless number that gives a measure of the ratio of inertial forces left( rho {bold mathrm V}^2 right) to viscous forces left( {{mu {bold mathrm V}} over {L}} right) and consequently quantifies the relative importance of these two types of forces for given flow conditions. The concept was introduced by George Gabriel Stokes in 1851, but the Reynolds number is named after Osborne Reynolds (1842-1912), who popularized its use in 1883. Reynolds numbers frequently arise when performing dimensional analysis of fluid dynamics problems, and as such can be used to determine dynamic similitude between different experimental cases. They are also used to characterize different flow regimes, such as laminar or turbulent flow: laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion, while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce random eddies, vortices and other flow instabilities.