Scruton number

The Scruton number (Sc) is an important parameter for vortex-induced vibration (excitation) of structures, vibrations caused by rain or wind, dry inclined cable galloping, and wake galloping, the unstable airflow that forms around bridge cables and other cylindrically-structured buildings. It is named after Christopher "Kit" Scruton, a British industrial dynamics engineer.

It is defined by:

$\mathrm {Sc} ={\frac {2\delta _{s}m_{e}}{\rho b_{\text{ref}}^{2}}},$

where

$\delta _{s}$	is the structural damping expressed by the logarithmic damping decrement,
$m_{e}$	is the effective mass per unit length,
$\rho$	is the density of the air, or liquid,
$b_{\text{ref}}$	is the characteristic width of the structure.