Complex Fluid Flows Simulated with New Open-Source Software on Any Grid Shape

Researchers are increasingly focused on accurately modelling multiphase flows, a significant challenge in many engineering applications. Ehsan Amani from Amirkabir University of Technology, alongside colleagues, have addressed a key limitation in current computational methods by developing cfdmfFTFoam, a new front-tracking solver implemented within the OpenFOAM computational fluid dynamics software. This work represents a substantial advance as it provides a pure front-tracking method applicable to general unstructured grids, overcoming the restrictions of existing open-source tools limited to structured or hybrid meshes. By integrating necessary communication and advection algorithms, and equipping the package with a variety of sub-algorithms, Amani et al. offer a versatile tool anticipated to accelerate future research and algorithm development within the field of front-tracking methodology.

This work introduces cfdmfFTFoam, a front-tracking solver designed to accurately model the interaction of multiple fluids on complex, unstructured grids.

Existing methods often rely on simplified grid structures or hybrid approaches, limiting their versatility and accuracy in simulating real-world phenomena. The newly created package integrates the Ftc3D front-tracking code with the widely used OpenFOAM computational fluid dynamics software, enabling simulations on general unstructured grids for both serial and parallel processing. cfdmfFTFoam employs the front-tracking method, a technique that explicitly tracks interfaces between different fluids using a Lagrangian surface mesh embedded within an Eulerian grid.
This approach offers advantages over other methods, including accurate representation of interface physics such as coalescence and breakup, precise calculation of interface normals and curvature, and reduced numerical dissipation during interface advection. The solver incorporates several key sub-algorithms, including front volume correction, remeshing techniques, tension computation, and indicator function construction, enhancing its robustness and capabilities.

Validation against standard multiphase flow benchmarks demonstrates the accuracy and reliability of cfdmfFTFoam. The development of this tool is anticipated to significantly facilitate future research into front-tracking methods and their application to a wide range of complex fluid flow problems. This advancement promises to improve the modelling of phenomena such as droplet collisions, spray breakup, and boiling processes.

The software is built upon OpenFOAM version 9, ensuring compatibility with a robust and actively maintained CFD platform. The implementation of necessary front mesh to Eulerian grid communication and front nodes advection algorithms allows for accurate tracking of interfaces even in complex geometries.

This capability is crucial for simulating realistic scenarios encountered in various engineering applications. By providing a pure front-tracking solver on general unstructured grids, cfdmfFTFoam removes limitations previously imposed by grid constraints and opens new avenues for investigating multiphase flow dynamics. The source code is publicly available, fostering collaboration and further development within the scientific community.

Implementation of a fully resolved front-tracking method within OpenFOAM nine

A triangulated front mesh forms the core of the cfdmfFTFoam package, enabling a fully resolved simulation of multiphase flows on general unstructured grids. This innovative approach circumvents the limitations of existing open-source front-tracking methods, which are typically restricted to structured Cartesian grids or hybrid mesh configurations.

The work began with integrating the Ftc3D front-tracking code into the OpenFOAM computational fluid dynamics software, specifically utilising OpenFOAM version 9. This integration necessitated the development of algorithms for communication between the front mesh and the Eulerian grid, alongside methods for advecting front nodes, ensuring accurate tracking of interface movement.

Crucially, the research team implemented a suite of sub-algorithms to enhance the functionality of cfdmfFTFoam. These included a front volume correction method to maintain accurate representation of interfacial volumes, a remeshing procedure to adapt the front mesh to complex flow conditions, and a tension computation algorithm to model surface tension effects.

Indicator function construction was also incorporated, allowing for clear identification of different phases within the flow field. Validations were performed against established multiphase flow benchmarks to confirm the solver’s accuracy and robustness. The methodology prioritised a pure front-tracking implementation, avoiding hybrid approaches to maintain computational efficiency and clarity.

Front mesh to Eulerian grid communication was achieved through a carefully designed interpolation scheme, ensuring minimal numerical diffusion. Front nodes were advected using a robust algorithm that accounts for mesh deformation and maintains mesh quality. The resulting cfdmfFTFoam package provides a versatile tool for investigating complex multiphase phenomena, offering a significant advancement in open-source interface tracking capabilities and facilitating future research in the field.

Implementation and validation of cfdmfFTFoam for multiphase flow simulations on unstructured meshes

Researchers have developed a new Front-Tracking Method (FTM) package, cfdmfFTFoam, integrated within the OpenFOAM computational fluid dynamics (CFD) software suite. This implementation facilitates simulations of multiphase flows on general unstructured grids, overcoming limitations found in existing open-source FTM solvers.

The work details a complete FTM solver, encompassing front volume correction, remeshing, tension computation, and indicator function construction, all designed for both serial and parallel computation. The cfdmfFTFoam package is built upon OpenFOAM version 9, ensuring compatibility with a widely used and actively developed CFD platform.

Assessments and validations were performed using standard multiphase flow benchmarks to confirm the solver’s accuracy and robustness. The solver’s structure centers around a PISO-SIMPLE or PIMPLE algorithm, coupled with six consecutive steps for front tracking at each time step: front volume correction, front remeshing, surface tension computation, front-to-field communication, indicator function construction, and front advection.

The core of the implementation resides within the “frontTrackingCloud” object, encapsulating Lagrangian surface mesh data and FTM procedures. The “evolve()” method directs all FTM sub-algorithms, updating mixture density, viscosity, and surface tension fields to solve the governing one-fluid Navier-Stokes equations.

A conservative smoothing filter, though not utilized in the validation examples, is included to enhance stability at the potential cost of reduced accuracy. The code structure closely mirrors the standard “interFoam” solver within OpenFOAM version 9, providing a familiar framework for users.

Implementation and validation of cfdmfFTFoam for unstructured grid multiphase flow simulations

A new computational framework, cfdmfFTFoam, facilitates detailed simulation of multiphase flows using the Front-Tracking Method on general unstructured grids. This advancement addresses a significant gap in open-source software availability for this technique, which previously was limited to simpler grid structures or hybrid approaches.

The implementation integrates the Ftc3D Front-Tracking Method into the OpenFOAM computational fluid dynamics software, enabling robust and versatile modelling of complex fluid interactions. The cfdmfFTFoam package incorporates essential algorithms for accurate front mesh management and communication with the Eulerian grid, crucial for simulating fluid behaviour across interfaces.

Features such as front volume correction, remeshing, tension computation, and indicator function construction enhance the solver’s capabilities and reliability. Validations against standard multiphase flow benchmarks demonstrate the solver’s accuracy and potential for application in a range of engineering and scientific problems.

The development is built upon OpenFOAM version 9, ensuring compatibility with a widely used and actively maintained platform. While the authors acknowledge the computational complexity inherent in Front-Tracking Methods, this new package provides a valuable tool for researchers seeking to improve algorithms and explore new applications. Future work may focus on optimising performance and extending the solver’s capabilities to handle more complex physical phenomena, but the current implementation represents a substantial step forward in accessible and versatile multiphase flow modelling.