ICSFoam: An OpenFOAM library for implicit coupled simulations of high-speed flows

When a strong coupling between the equations of a specific physical problem exists, segregated solvers are likely to struggle or fail in finding the solution to the equation system. In this work, we propose an intuitive and physically-sound method that allows for block-coupled simulations in the OpenFOAM (OF) framework. First, we build and describe in detail the code structure for the assembly, storage, and solution of the system matrix for finite volume discretizations. This framework is the backbone for the implementation of the block-coupled solver we present after. Great attention is focused on the implementation of an implicit density-based solver, which represents a novelty in the OF context. A wide variety of test cases is proposed with the specific aim of assessing the performance of the new solver on different problems. Where possible, a comparison with other built-in OF solvers or other software is presented. It is shown that the new solver outperforms the current explicit density-based OF solver and shows similar, if not better, performances compared to other opensource and commercial softwares. In a fully opensource philosophy, the library files are freely accessible in the authors repository at the link: https://github.com/stefanoOliani/ICSFoam.