Multiphase solvers handle flows with two or more distinct fluid phases (water + air, oil + water, gas-liquid systems) and the interfaces between them. They capture gas-liquid phase transformation such as boiling, evaporation, and condensation, and use the Volume of Fluid (VOF) method to track interface positions over time.
These solvers are defined in the system but are currently reserved for a later phase of the platform. The agent detects multiphase scenarios (boiling, cavitation, evaporation, condensation) and warns when a multiphase solver would be needed.
How the agent detects multiphase cases
The solver selector identifies multiphase scenarios by looking for:
- Multiple fluid phases (water + air, oil + water)
- Phase change keywords: boiling, cavitation, evaporation, condensation, flashing
- Moving fluid-front scenarios (dam break, wave, filling)
- Gas-liquid phase transformation (boiling, condensation, evaporation)
- Cryogenic liquid heated above its boiling point (e.g., LN₂ at 77.4 K heated past 87 K)
When detected, the agent warns the user and attempts a best-effort heuristic rather than silently picking an incompatible single-phase solver.
Solver reference
interFoam2-phase VOF, incompressibleThe standard two-phase Volume of Fluid solver for incompressible flows. Uses algebraic interface compression (MULES) to track the interface between two immiscible fluids like water and air. Pressure field is p_rgh (kinematic, modified for hydrostatic head). Requires constant/g. No energy equation.
Use cases: Dam breaks, wave tanks, sloshing, oil-water separation, spillway flows
interIsoFoam2-phase VOF, incompressible, geometric interfaceSame physics as interFoam but uses geometric interface reconstruction (isoAdvector) instead of algebraic MULES compression. Produces sharper interfaces with less numerical diffusion, especially useful for thin films and fast impacts.
Use cases: Droplet impacts, thin film flows, precise interface tracking where MULES smears
compressibleInterFoam2-phase VOF, compressible, non-isothermalExtends interFoam to compressible, non-isothermal two-phase flows. Requires both p_rgh and p pressure fields, temperature field, and per-phase thermophysical properties. Supports cryogenic fluids with icoPolynomial EOS for density-temperature coupling.
Use cases: LN₂ boiloff, steam-water systems, cryogenic tank sloshing, compressible two-phase with heat transfer
compressibleInterIsoFoam2-phase VOF, compressible, geometric interfaceCombines compressibleInterFoam physics with geometric interface reconstruction. Same requirements as compressibleInterFoam but with sharper interfaces.
Use cases: Same as compressibleInterFoam where interface sharpness is critical
compressibleMultiphaseInterFoamN-phase VOF (N ≥ 3), compressibleHandles three or more phases simultaneously. Requires a composite alpha field (alphas) plus individual alpha fields per phase. Each phase has its own thermophysicalProperties file. Surface tension is defined for each pair of phases.
Use cases: Oil-water-air systems, liquid-vapor-gas mixtures, multi-fluid stratification
Common configuration rules
All multiphase solvers share these requirements:
constant/gis always required (gravity drives hydrostatic pressure splitting)- Compressible variants require both
0/p_rghand0/p - PIMPLE
nOuterCorrectors ≥ 2is mandatory for compressible variants maxCo 0.5(not 1.0) for numerical stability- GAMG smoother must be
GaussSeidel - Never generate
system/fvOptionsfor multiphase solvers (causes fatal error)
Cryogenic fluid handling
The agent auto-detects cryogenic fluids by name or by inlet temperature below 130 K. Known boiling points:
| Fluid | Boiling point |
|---|---|
| LHe | 4.2 K |
| LH₂ | 20.3 K |
| LN₂ | 77.4 K |
| LAr | 87.3 K |
| LOX | 90.2 K |
| LNG | 111.7 K |
If the maximum boundary condition temperature exceeds the boiling point by more than 10 K, the agent flags a phase-change scenario. See Custom Fluid Properties for how the agent configures thermophysical properties for fluids not natively supported by OpenFOAM.