The Grashof number is a dimensionless parameter which, unlike the Rayleigh number, contains information of a mechanical nature only. It contrasts the exclusive effects of viscosity with the floating force:
\[Gr=\dfrac{F_g}{(F_v)^2}\]
once the motion is triggered (Ra > 1708) to understand if the motion is laminar or turbulent (in natural convection) the Grashof number is evaluated; if (Gr > \(10^9\)) the motion is laminar, if instead (Gr < \(10^9\)) the motion is turbulent.
In natural convection:
\[Gr=\dfrac{\rho^2g\beta\Delta TL^3}{\mu^2}\]