LENT - a hybrid LEvel-set / froNT tracking (LENT) method in OpenFOAM

The LENT OpenFOAM module implements the LENT hybrid unstructured Level Set / Front Tracking method for DNS simulations of two-phase flows using a collocated unstructured FVM equation discretization.

IMPORTANT: this is an actively developed research code. Report bugs here, contact us directly regarding possible features or applications.

Developers

Tomislav Maric maric{a}mma[dot]tu-darmstadt[dot]de

Tobias Tolle tolle{a}mma[dot]tu-darmstadt[dot]de

Jun Liu liu{a}mma[dot]tu-darmstadt[dot]de

Mathematical Modeling and Analysis Institute,Mathematics Department, TU Darmstadt

Publications

Liu, Jun, Tobias Tolle, Dieter Bothe, and Tomislav Maric. "A collocated unstructured finite volume Level Set/Front Tracking method for two-phase flows with large density-ratios." arXiv preprint arXiv:2109.01595 (2021). arXiv:2109.01595

Tolle, Tobias, Dieter Bothe, and Tomislav Marić. "SAAMPLE: A segregated accuracy-driven algorithm for multiphase pressure-linked equations." Computers & Fluids 200 (2020): 104450. doi:10.1016/j.compfluid.2020.104450 arXiv:2001.09775

Marić, Tomislav, Holger Marschall, and Dieter Bothe. "lentFoam–A hybrid Level Set/Front Tracking method on unstructured meshes." Computers & Fluids 113 (2015): 20-31. doi: 10.1016/j.compfluid.2014.12.019

Installation

Prerequisites

• OpenFOAM versions: OpenFOAM v2112 (ESI)
• Compilers: gcc 10.3.0 and earlier
• Build system: CMake 3.14 or higher
• git for fetching dependencies
• gmsh or paraview for surface mesh generation
• admesh for normal consistency (only for some 2D test cases)

Compilation and installation

LENT is using the CMake build system. Make sure that you have sourced OpenFOAM's bashrc so that the OpenFOAM environment variables are set properly. Then execute the following commands inside the lent directory:

mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=./ -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=on ..
make && make install

This will configure, compile and install the lent library and its applications to $FOAM_USER_LIBBIN and $FOAM_USER_APPBIN, respectively. Valid build types are Release, Debug and RelWithDebInfo. The flag -DCMAKE_EXPORT_COMPILE_COMMANDS=on is optional.
Alternatively, you can run the install.sh script given that gcc-10 and g++-10 are available on your system.
Lent comes with some scripts, e.g. to setup and run parameter studies. To be able to use them, you need to add the scripts directory to your PATH variable by executing the following command in your shell:

echo 'export PATH=$HOME/OpenFOAM/openfoam/lent/scripts:$PATH' >> $HOME/.bashrc
. $HOME/.bashrc

This command assumes that Lent is located in ~/OpenFOAM/openfoam. If this is not the case, change the path accordingly.

Installing PyFoam

PyFoam scripts are used directly by some LENT utilities, so PyFoam needs to be installed on the system. Information on PyFoam installation can be found on the OpenFOAM Wiki.

Usage

There are two important utilities that are distributed with the LENT repository which are used to prepare the simulation case:

• lentClearCasesRecursive - pyFoam based script that cleans the LENT cases recursively
• lentSetFields - pre-processing application that sets the signed distance and cell search fields required by the LENT method
• lentCreateFront - create a surface STL file based on an analytical surface description.

for the lent solvers:

• lentReconstruct - solver application used to reconstruct the LENT front
• lentAdvect - solver application used to advect the LENT front with a prescribed velocity field
• lentFoam - solver application used to execute two-phase Direct Numerical Simulations with the LENT method

Other testing and utility applications are available in the applications folder with the appropriate descriptions placed in the implementation file headers.
In cases/flow-solution/translating-droplet/three-dimensional there are several run scripts providing examples on the usage of scripts and solvers.

Utilities information

lentClearCasesRecursive

• Expects to find 0.org directory with the original fields in the simulation case directory. The LENT method modifies the initial 0 time-step directory, as it requires the signed and search distance fields to be computed before the start of the simulation.
• Is used mostly for validation cases of the lent-validation-cases repository.
• Even if 0.org doesn't exist, it will clean up the front/front-000*.vtk files written from the last run.

lentSetFields

• Requires a file named front.stl in the folder front of the LENT simulation case.
• It uses the surface mesh stored in the front.stl file to pre-process the signed and search distance fields.

lentCreateFront

• Requires a dictionary named frontSurface in system/lentSolution specifying the surface.
• It uses the reconstruction procedure to generate a triangular surface mesh for the given surface and saves it as constant/front.stl.

Running cases

This is the standard workflow:

lentClearCasesRecursive
lentSetFields
lentFoam 

lentFoam can be replaced by another solver application (lentReconstruct or lentAdvect).