Add JWL equation of state and detonation modeling for the five-equation model

[fahnab666]

Summary

Add a Jones-Wilkins-Lee (JWL) equation of state and a detonation modeling capability to the five-equation Allaire model (model_eqns = 2). A JWL fluid should be selectable per material (e.g. fluid_pp(i)%eos = 2) and coexist with an ideal-gas or stiffened-gas ambient, so MFC can simulate explosive products expanding into air or water.

Motivation

MFC currently has no equation of state for detonation products, so simulations involving high explosives, program burn, or detonation-driven blast waves are out of reach. This was previously raised in #1384, which asked whether JWL support was feasible; it was closed without an implementation landing. Detonation-driven multiphase problems (blast loading, underwater explosions, explosively driven bubble collapse) are a natural extension of MFC's existing multi-fluid and immersed-boundary/Euler-Lagrange capabilities, and several groups have asked for this EOS.

Proposed capability

• JWL pressure law for pure products:

$$p = A\left(1-\frac{\omega}{R_1V}\right)e^{-R_1V} + B\left(1-\frac{\omega}{R_2V}\right)e^{-R_2V} + \omega\rho e, \qquad V=\frac{\rho_0}{\rho}.$$

• A composition (heat-capacity) weighted mixture closure between JWL products and an ideal-gas or stiffened-gas ambient, with a closed-form pressure-energy inverse and analytic sound speed (no iterative solve), degenerating exactly to pure JWL and to the ambient law at the mixture endpoints.
• Optional reaction sources, off by default:
  • Kinematic program burn (front expanding from a detonation point at $D_{cj}$)
  • Products-air afterburn with an advected progress variable
  • JWL++ (Souers 2000) pressure-driven self-propagating reactive burn
• Coupling with existing capabilities: immersed boundaries and Euler-Lagrange bubbles.
• Validation against known solutions: exact Riemann star states, ZND detonation structure vs. the analytic Hugoniot/Rayleigh/CJ construction, Sedov-Taylor blast scaling, and far-field TNT overpressure vs. Kinney-Graham.

Notes

• Some existing features are expected to be incompatible with the JWL closure at first (wave_speeds = 2, CBC boundaries, alt_soundspeed, elasticity, igr, bubbles_euler, mhd, chemistry); these should be checked and rejected at startup and in ./mfc.sh validate.
• A Mie-Gruneisen N-constituent pressure-equilibrium closure (products, water, and air together) is a natural follow-up but out of scope for the initial implementation.
• A Kuhl-model implementation of the mixture closure path is also being kept open for future improvement, as an alternative to the composition-weighted closure landed initially.

References

• Souers, P.C. et al., JWL++: A Simple Reactive Flow Code Package for Detonation, Propellants, Explosives, Pyrotechnics 25 (2000).
• Garno, J.M. et al. (2020), reactant energy offset for resolved ZND structure.

Related: #1384