VariationalBarotropicFluid

This is the simplest variational compressible-fluid model in Struphy.

It keeps only density and velocity and uses a barotropic closure rather than a separate entropy or pressure evolution equation.

This model is appropriate for:

• barotropic compressible-flow benchmarks
• testing variational density and momentum propagators
• reduced fluid studies without entropy evolution

PDEs solved by model:

Continuity:

Momentum:

where the internal energy per unit mass is $\mathcal{U}(\rho )=\rho /2$.

The reference flow speed is the Alfvén speed and the internal energy is

scaled with density:

Time integration is performed by the following propagators (in sequence):

1. VariationalDensityEvolve
2. VariationalMomentumAdvection

The following scalars are tracked during simulation:

• Kinetic energy: kinetic_energy
• Thermodynamic energy: thermo_energy
• Total energy: total_energy