# Rayleigh number

Jump to: navigation, search

The Rayleigh number is the ratio of the buoyancy force to the viscous force in a medium.

$Ra = \frac{g \alpha \Gamma d^4}{\nu \kappa}$

where $g =$ acceleration due to gravity, $\alpha =$ coefficient of thermal expansion, $\Gamma =$ background temperature gradient, $d =$ length scale of flow, $\nu =$ kinematic viscosity and $\kappa =$ thermal diffusivity