Dimensionless quantity characterising the ratio of inertial forces to viscous forces and corresponding fluid flow regime:
| (1) | {\rm Re} = \frac{u \, d}{\nu} = \frac{\rho \, u \, d}{\mu} |
where
u | average cross-sectional flow velocity |
d | characteristic linear dimension of the fluid conduit |
\rho | fluid density |
\mu | dynamic viscosity |
\nu | kinematic viscosity |
The physical meaning of Reynolds number is the ratio of Inertial forces to Viscous forces:
| (2) | {\rm Re} = \frac{{\rm Inertial} \ {\rm forces}}{{\rm Viscous} \ {\rm forces}} = \frac{u \, d}{\nu} |
See also
Physics / Fluid Dynamics / Fluid flow regimes
[ Reynolds number in Pipe Flow]