[WIP] Standard initialization for Incompressible flows using thermodynamic_pressure and the Inc_Temperature_init

[Cristopher-Morales]

Proposed Changes

With this pull request, we aim to initialize the fluid models based on the Ideal gas laws for incompressible flows in a standard way using the THERMODYNAMIC_PRESSURE($P_{op}$) and the INC_TEMPERATURE_INIT ($T_{init}$), the initial density is computed based on the ideal gas law :

$\rho_{init}= P_{op} / R T_{init}$

When the FLUID_MODEL is CONSTANT_DENSITY, the constant density must be given in the config file using the option DENSITY_CONSTANT, similar as it is done when viscosity, thermal conductivity and diffusivity models are chosen as constant.

Related Work

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[TobiKattmann]

I am trying to find some time to think about how to do a bit of option-consolidation on the non-dimensionalization side and initialization is quite a bit linked to that process -> I hope to open a discussion with some more information and proposal soon -> And since this PR is looking to change the INC_DENSITY_INIT option which is part of that my request would be to maybe spare that option up to the conference (the init change to use thermodynamic pressure is a little more independent of that I think via pedros suggestion to mimic what we do for compressible flow atm)