Fluid models

Section Aims

This section aims to:

  • Describe the fluid models available within solids4foam;
  • Provide insight into the different solver types and their intended use cases.

What is a Fluid Model?

In solids4foam, fluid models are classes which solve the governing equations in a fluid domain, primarily to calculate the velocity and pressure fields. These fluid models (base class fluidModel) can be interpreted as modular solvers, packaged into a class structure so that they can be selected at runtime and combined with solid models in fluid-solid interaction analyses.

Each fluid model manages its own mesh, time-stepping and boundary conditions. The base class provides the velocity (U), pressure (p), volumetric flux (phi), and related fields that coupling interfaces use to transfer loads and displacements between the fluid and solid domains.

Fluid Models Available in solids4foam

Here, we list the fluid models currently available in solids4foam, and briefly summarise their characteristic features.

  • Incompressible single-phase models

    • pimpleFluid: transient incompressible Newtonian fluid solver based on the PIMPLE (merged PISO-SIMPLE) algorithm; the most commonly used fluid model in solids4foam FSI analyses.
    • newtonIcoFluid: incompressible laminar solver using a Jacobian-free Newton-Krylov approach via the PETSc SNES interface; suitable for cases where a fully implicit nonlinear solve is preferred.

  • Incompressible multi-phase models

    • interFluid: two-phase flow solver with volume-of-fluid (VOF) interface capturing, based on the interFoam family of solvers; supports dynamic meshes for FSI with a free surface.

  • Compressible models

    • sonicLiquidFluid: transient compressible solver for weakly compressible liquids (sonic liquid), based on the sonicLiquidFoam solver.

  • Specialised models

    • pimpleOversetFluid: a variant of pimpleFluid with dynamic mesh and overset (Chimera) mesh support; currently only available with foam-extend.
    • oneWayFsiFluid: a pseudo-fluid model that reads pre-computed velocity and pressure fields from a previously run fluid case; no fluid equations are solved. Used for one-way FSI where the fluid loading is known in advance.

Notes

  • All fluid models support dynamic meshes for use in FSI analyses, where the fluid domain deforms in response to solid motion.
  • The pimpleFluid model is available for all supported OpenFOAM variants (OpenFOAM.com, OpenFOAM.org, and foam-extend), whereas some models are variant-specific.
  • For one-way FSI (fluid drives solid, but solid does not affect fluid), use oneWayFsiFluid together with the oneWayCoupling fluid-solid interface.