openCFS: Open Source Finite Element Software for Coupled Field Simulation -- Part Acoustics
Stefan Schoder, Klaus Roppert
TL;DR
openCFS provides an open-source finite element framework for coupled-field simulations with a focus on acoustics, offering standard and variant wave equations, flexible FE formulations, and a Python API for rapid experimentation. The paper details the mathematical formulations (standard, frequency-dependent, spatially varying, and convective wave equations), FE assembly, and simulation runtime lifecycle, including an XML-driven workflow and non-conforming/mortar interfaces. It also showcases acoustic postprocessing, viscous acoustics, and aeroacoustic applications, highlighting the software’s capability to couple acoustics with mechanics and flow sources. The work emphasizes open, extensible design, modular workflows, and concrete future directions such as time-domain dispersive materials, PML automation, and mortar-method enhancements, underscoring its practical impact for industrial and research aeroacoustic problems.
Abstract
The finite element method offers attractive methods for the numerical solution of coupled field problems arising in sensors and actuator simulations of various physical domains, like electrodynamics, mechanics, and thermodynamics. With this application perspective and being open, accessible, and fast implementations are possible, openCFS was launched in 2020. It provides an open-source framework for implementing partial differential equations using the finite element method. In particular, the acoustic module is part of active development, including several key methods. These methods include the perfectly-matched layer technique, non-confirming interface formulations, Lagrangian basis function, Legendre basis functions, spectral element formulations, a nodal element type, edge-based element type (aeroacoustic post-processing), absorbing boundary conditions, frequency dependent-material for time-harmonic and time-dependent simulations. Time-dependent simulations, time-harmonic simulations, and eigenvalue simulations are supported. Several variants of acoustic equations are implemented, including the relevant source terms and wave operators for aeroacoustics. The package includes rotating domains and non-conforming interfaces for fan noise simulations. It also contains an API to the Python3 package pyCFS. This paper presents openCFS with a focus on the acoustic module.