Add Sutherland's law to compressible Navier-Stokes

[jlchan]

Use Sutherland's law to get the molecular and thermal diffusivity in CompressibleNavierStokesDiffusion2D.

Originally posted by @sloede in #1156 (comment)

[DanielDoehring]

I planned to look into this for the aerodynamic simulations.

Since in that case $\mu = \mu\big(T(\boldsymbol x)\big)$ the derivatives (gradient & divergence) complicate due to the chain rule.
Is this in general accounted for, or do people use only temperature dependent viscosity in the flux, but drop the dependence on space?

[andrewwinters5000]

do people use only temperature dependent viscosity in the flux, but drop the dependence on space?

In FLUXO we only use a temperature dependent viscosity see here.

[DanielDoehring]

I.e., the only real change would be re-computing the dynamic viscosity

https://github.com/trixi-framework/Trixi.jl/pull/1808/files#diff-8e1a56d54ddffada1448f2d79a97dcc9ee1d5ea3e91e96311d8bf7f65c968114R358-R359

and leaving the rest untouched?

[andrewwinters5000]

Yes, I believe this should be all that is necessary.

[DanielDoehring]

Question is if we want to use the standard version
$$
\mu (T) = \mu_0 \frac{T_0 + C}{T + C} \bigg ( \frac{T}{T_0} \bigg )^{ \frac{3}{2} }
$$

or the extended one present in FLUXO.