Fluca

A computational fluid dynamics (CFD) framework for incompressible viscous flows on Cartesian grids, built on PETSc.

Overview

Fluca solves the incompressible Navier-Stokes equations using finite differences on collocated Cartesian grids with pressure stabilization. Time integration uses the Segregated Runge-Kutta (SRK) method, which decouples the velocity-pressure system into Helmholtz and Poisson solves at each stage.

Features

• Collocated grid: Cell-centered velocity and pressure with pressure stabilization
• FlucaFD operators: Composable finite difference operators (derivatives, compositions, scaling, sums, TVD schemes)
• Segregated Runge-Kutta: IMEX time integration with 12 selectable schemes (Bakhvalov, 2025)
• Physics models: Modular Phys abstraction with incompressible Navier-Stokes (PhysINS) subtype
• Parallel computing: MPI-based parallelization through PETSc
• CGNS I/O: Standard file format support for solution data

Build

Dependencies

• CMake: >= 3.20
• C Compiler: Compatible with PETSc
• PETSc: >= 3.23
• HDF5: Required by CGNS
• CGNS: Must be built with parallel I/O support enabled

Building

cmake -B build
cmake --build build

Running Tests

ctest --test-dir build -R tests_       # Unit tests (fast)
ctest --test-dir build -R tutorials_   # Tutorial tests (slow)

CMake Options

• PETSC_DIR: Path to PETSc
• HDF5_DIR: Path to HDF5
• CGNS_DIR: Path to CGNS
• FLUCA_USE_PETSC_CC: Use the C compiler that was used to build PETSc (default: ON); if OFF, Fluca uses the compiler defined in CMAKE_C_COMPILER

Getting Started

See QUICK_START.md for a step-by-step guide to building simulations with Fluca.

Theory Guide

See THEORY_GUIDE.md for the mathematical formulation and numerical methods.

Output

Fluca uses the CGNS format for output files. You can visualize results using standard CFD post-processing tools such as ParaView or Tecplot.

Development

Code Style

The project uses clang-format for code formatting. The configuration file .clang-format, adopted from PETSc, is provided in the repository.

For other style guidelines, such as naming conventions or formatting not covered by clang-format, refer to the PETSc Style and Usage Guide.

Pre-commit Hooks

Pre-commit hooks are configured in .pre-commit-config.yaml. Install them with:

pip install pre-commit
pre-commit install

License

This project is licensed under the BSD 3-Clause License. See the LICENSE file for details.

References

• PETSc: https://petsc.org/
• CGNS: https://cgns.github.io/
• S. Bakhvalov, Segregated Runge-Kutta methods for the incompressible Navier-Stokes equations, arXiv:2506.09519 (2025)