ENH: SpalartAllmaras: add estimation functions for k, epsilon and omega

Summary

• Adds estimation functions for k, epsilon, omega fields into the SpalartAllmaras turbulence closure model, so that various utilities can be enabled with this model if necessary, e.g. turbulenceFields function object.
• Reduces peak-memory usage in the SpalartAllmaras model.

Resolved bugs

N/A

Details of new models

• The first test case was based on a direct-numerical simulation by (Moser et al., 1999). The test case is a smooth-wall turbulent plane channel flow wherein an internal flow statistically develops downstream (until is fully developed) through parallel smooth walls that are two characteristic-length apart. The friction Reynolds number of the flow is
  $\mathrm{Re}_\tau = 180$
  .

Turbulent kinetic energy

Turbulent kinetic energy dissipation rate

Turbulent kinetic energy production rate

Streamwise flow speed

Reynolds stress tensor components

Risks

No known risks or user-input changes.

PS: Hi @vaggelisp, might affect or be relevant? just for your info in any case.