Dear Kratos users:

We are currently considering a reorganization of the FluidDynamics application. Since we consider it a core component of Kratos Multiphysics, we should be particularly careful in ensuring that it is stable and robust, but we find that it has been growing out of control in recent times. To manage it, we are considering the possibility of dividing it into a stable, tested and documented core and a more experimental derived application, containing extensions, innovations and problem-specific solutions.

Before we go forward with this proposal, we would like to hear the opinion of the community. In particular, we are interested in the following:

1. Would this approach cause problems for your particular situation?

2. Are there backwards compatibility issues that should be addressed? That is: do you rely on the particular implementations of any of the current components and would moving them around (and maybe deprecating some, replacing them by newer implementations) cause trouble for you?

3. What should be considered "core" and what is "extra"? In this sense, we are proposing to consider the components at the end of this post (exclusively) as core.

4. Should turbulence models be part of the FluidDynamics application or should they be moved to a specific (derived) application?

What follows is the proposal for the new core of the FluidDynamicsApplication

Solver | Geometries | Embedded | Two-phase | Time scheme | Turbulence | Non-Newtonian |

Monolithic Navier-Stokes | triange, tetrahedra, quadrilateral, hexahedra | No | No | Bossak, BDF2 | Yes | No |

Embedded Monolithic Navier-Stokes | triange, tetrahedra | Yes | No | BDF2 | No | No |

Two-phase Monolithic Navier-Stokes | triange, tetrahedra | No | Yes | BDF2 | No | Yes |

Fractional step Navier-Stokes | triange, tetrahedra, quadrilateral, hexahedra | No | No | BDF2 | Yes | No |

Embedded FS Navier-Stokes | triange, tetrahedra | Yes | No | BDF2 | Yes | No |

Monolithic Stokes | triange, tetrahedra | No | No | BDF2 | No | Yes |

Two-phase Monolithic Stokes | triange, tetrahedra | No | Yes | BDF2 | No | Yes |

Monolithic Navier-Stokes Solvers:

- Monolithic solver: New implementation, using the same formulation (ASGS/OSS) as the current one but with support for quadrilaterals/hexahedra.

Supported geometries: triangles, quadrilaterals, tetrahedra, hexahedra.

Time scheme: Velocity Bossak (the current default) or BDF2.

Support for turbulence: Any model based on an eddy viscosity.

No support for non-Newtonian constitutive laws.

- Embedded monolithic solver (new implementation)

Supported geometries: triangles, tetrahedra.

Time scheme: BDF2 only

Support for turbulence: Not planned.

Support for non-Newtonian constitutive laws.

- Two-phase Monolithic incompressible Navier-Stokes (New implementaiton)

Supported geometries: triangles, tetrahedra.

Time scheme: BDF2 only

Support for turbulence: No

Support for non-Newtonian constitutive laws.

Segregated (fractional step) incompressible Navier-Stokes solvers

- Fractional Step solver (body-fitted geometries only)

The current segregated incompressible solver implementation, extending support to quadrilaterals/hexahedra

Supported geometries: triangles, quadrilaterals, tetrahedra, hexahedra.

Time scheme: BDF2

Support for turbulence: Any model based on an eddy viscosity.

No support for non-Newtonian constitutive laws.

- Embedded fractional step (non-body-fitted meshes): current implementation.

Supported geometries: triangles, tetrahedra.

Time scheme: BDF2

Support for turbulence: Any model based on an eddy viscosity.

No support for non-Newtonian constitutive laws.

Stokes flow solvers

- Stokes flow (body-fitted geometries): New implementation

Supported geometries: triangles, tetrahedra.

Time scheme: BDF2 only

Support for turbulence: No.

Support for non-Newtonian constitutive laws.

- Two-phase Stokes flow (new implementation)

Supported geometries: triangles, tetrahedra.

Time scheme: BDF2 only

Support for turbulence: No

Support for non-Newtonian constitutive laws.

Anything not on the list would go to a new "experimental" CFD application. Solvers that support turbulence will also support wall law boundary conditions. Otherwise, only inlet, no-slip or no-penetration boundary conditions should be available.