Feature: NASA polynomial gas model implementation (CNasaGas)

[Omgiri01]

Summary

This PR implements a NASA polynomial-based specific heat model (CNasaGas) in SU2. This allows for temperature-dependent thermophysical property calculations ($C_p$, enthalpy, and entropy) using the standard NASA 7-coefficient format.

Motivation

Accurate simulation of high-temperature or hypersonic flows requires temperature-dependent specific heats. This bridges the gap for users who need more realism than a constant-property ideal gas model.

Key Changes

• Added CNasaGas class (inherits from CIdealGas).
• • Integrated a Newton-Raphson solver for T-from-energy inversion.
• • Added 3 new config options: NASA_CP_LOW_COEFFS, NASA_CP_HIGH_COEFFS, and NASA_T_TRANS.
• • Updated CEulerSolver and CFEM_DG_EulerSolver for non-dimensionalization.
• • Updated stagnation property calculations in CFlowOutput.

Related Work

This contribution is part of a GSoC 2026 project focusing on advanced thermodynamic modeling in SU2.

PR Checklist

• I am submitting my contribution to the develop branch.
• - [x] My contribution generates no new compiler warnings.
• - [x] My contribution is commented and consistent with SU2 style.
• - [x] I have updated appropriate documentation.

[bigfooted]

please do not waste our time with this.

[Omgiri01]

Hi @bigfooted, I apologize for the oversight in the previous submission. I realize now that the PR contained unrelated commits (Python Speed of Sound and Custom Thermal Boundaries) and some perceived overlap with PR #2705, which was poor practice on my part.

However, I'd like to clarify that this implementation (NASA-7 format specifically for compressible flows with a Newton-Raphson temperature inversion) is technically distinct from the incompressible NASA-9 model currently in #2705. The compressible solver requires this temperature inversion which is not present in the other PR.

I would like to resubmit a clean, atomic version of the NASA-7 model if the maintainers are open to it. Thank you for your time and guidance.