Grashof number

The Grashof number is a dimensionless number in fluid dynamics which approximates the ratio of the buoyancy force to the viscous force acting on a fluid.

$Gr={\frac {g\beta (T_{s}-T_{\infty })L^{3}}{\nu ^{2}}}\,$

where

g = acceleration of gravity

β = volumetric thermal expansion coefficient

T_s = source temperature

T_∞ = quiescent temperature

L = characteristic length

ν = kinematic viscosity