Sutherland viscosity law

Laminar dynamic viscosity is evaluated with the Sutherland formula, both in dimensional form (reference tables) and nondimensional form (solver working variables).

Nondimensional form

With \(T\) and \(t_s\) already scaled by the reference temperature:

\[\frac{\mu}{\mu_{\mathrm{ref}}} = T^{3/2}\frac{1+t_s}{T+t_s}\]

Dimensional form

\[\mu(T) = \mu_0 \left(\frac{T_0+T_s}{T+T_s}\right) \left(\frac{T}{T_0}\right)^{3/2}\]

Default air constants in Sutherland::Init: \(T_0=273.16\,\mathrm{K}\), \(T_s=110.4\,\mathrm{K}\), \(\mu_0=1.715\times 10^{-5}\,\mathrm{Pa\,s}\).

Pure APIs: SutherlandViscosityNondim, SutherlandViscosityDim (Sutherland.h). Class methods delegate to these. Tests: sutherland_policy_test.