About

FLEXI-PARTICLE is a high-order numerical Eulerian-Lagrangian framework for solving PDEs, with a special focus on Computational Fluid Dynamics. FLEXI is based on the Discontinuous Galerkin Spectral Element Method (DGSEM), which allows for high-order of accuracy and fully unstructured hexahedral meshes. The solver is parallelized very efficiently for large-scale applications and scales to 500,000+ cores. Moreover, FLEXI comes with a capable pre- and postprocessing suite that enables complex simulation setups up to the finished visualization.

For the main development branch, see flexi-framework/flexi. This repository contains an extension of FLEXI towards particle-laden flows. The particle tracking approach operates in physical space and is based on methods from ray-tracing to handle intersections with possibly curved boundaries. Particles are implemented with a Lagrangian point-particle ansatz and can either be one- or two-way coupled to the fluid phase. Particle-wall interactions are handled via a hard-sphere approach, where multiple models are available.

For details on the available models and implementation, see our paper in Computer Physics Communications or the manuscript on arxiv.

FLEXI has been developed by the Numerics Research Group (NRG) founded by Prof. Claus-Dieter Munz and currently lead by Prof. Andrea Beck at the Institute of Aerodynamics and Gasdynamics at the University of Stuttgart, Germany.

You can find detailed installation instructions, the extensive documentation and several tutorial cases for FLEXI here.

FLEXI is Copyright (C) 2016, Prof. Claus-Dieter Munz and is released under the GNU General Public License v3.0. For the full license terms see the included license file.

Numerous people have worked on and with FLEXI over the last years. We would like to thank all these contributors for their efforts they spent on building FLEXI.

In case you have questions regarding FLEXI or want to contribute yourself by either reporting bugs, requesting features or adding somthing different to the project, feel free to open an issue or pull request.

Cite

FLEXI is a scientific project. If you use FLEXI-PARTICLE for publications or presentations in science, please support the project by citing it. As general reference, please cite

Kopper, P., Schwarz, A., Copplestone, S. M., Ortwein, P., Staudacher, S., and Beck, A.
A framework for high-fidelity particle tracking on massively parallel systems
Computer Physics Communications, 289, (2023), 108762

or use the following Bibtex files

@article{flexi_particle,
 title     = {A framework for high-fidelity particle tracking on massively parallel systems},
 author    = {Kopper, Patrick and Schwarz, Anna and Copplestone, Stephen M. and Ortwein, Philip and Staudacher, Stephan and Beck, Andrea},
 journal   = {Computer Physics Communications},
 year      = {2023},
 month     = aug,
 pages     = {108762},
 doi       = {10.1016/j.cpc.2023.108762},
 publisher = {Elsevier},
}

To refer to specific applications and features, you can also cite the appropriate paper from this list.

Quick Start Guide

For a more detailed installation instructions, please see the documention here.

FLEXI is tested for various Linux distributions including Ubuntu, OpenSUSE, CentOS, or Arch. FLEXI also runs on macOS. For the installation, you need the following dependencies:

Package	Required	Installed by FLEXI
Git	x
CMake	x
C/C++ Compiler	x
Fortran Compiler	x
LAPACK/OpenBLAS	x	x
HDF5	x	x
MPI	(x)

The MPI library is only required for running parallel simulations on multiple ranks. The HDF5 and LAPACK libraries can are optionally built and locally installed during the FLEXI build process. The names of the packages and the package manager might differ depending on the specific distribution used.

Getting the code

Open a terminal, download FLEXI via git and optionally export the FLEXI directory:

git clone git@github.com:flexi-framework/flexi-particle.git
export FLEXI_DIR="$(pwd)/flexi"

Compiling the code

Enter the FLEXI directory, create a build directory and use CMake to configure and compile the code

cd $FLEXI_DIR
mkdir build; cd build
cmake ../
make

The executable flexi is now contained in the FLEXI directory in build/bin/. Custom configurations of the compiler options, dependencies, and code features can be set using

ccmake ../

Running the code

Navigate to the directory of the tutorial cavity and run FLEXI

cd $FLEXI_DIR/tutorials/cavity
$FLEXI_DIR/build/bin/flexi parameter_flexi.ini

Used libraries

FLEXI uses several external libraries as well as auxiliary functions from open source projects, including:

• CMake
• FFTW
• HDF5
• LAPACK
• MPI
• OpenMP
• OpenBLAS
• PAPI
• Reggie2.0