Different complexity in physical laws (e.g. to calculate viscosity)
For some physical laws there are several ways to calculate them. For example the viscosity of the component air (material/components/air.hh) is currently implemented in four ways: oldGasViscosity, gasViscosity, simpleGasViscosity, exactGasViscosity. Only gasViscosity is used. The same might be the case for other components and for other physical laws (e.g. density). In addition, the useComplexRelations switch in the FluidSystem enables the calculation of the viscosity or density based on the composition or on a main component (however, one could rename useComplexRelations to make this clear). This task might also be extended to e.g. permeability-porosity relationships, where also different ways of calculation exist. How do we want to treat this? We could:
- have one law implemented and leave it to the user to change the code (that means some code will be lying around useless as of now in air.hh)
- have an intelligent way to switch between different laws