The Flexi framework is engineered to efficiently solve the unsteady compressible Navier-Stokes equations and more. Its primary focus lies in applications such as DNS and LES of both internal and external compressible flows. Thanks to its open-source nature under GPL V3.0, Flexi and its tools are freely accessible to all users. Furthermore, its intuitive algorithmic design, combined with a vibrant community and comprehensive documentation, guarantees a seamless process for customizing or expanding Flexi to meet specific requirements. This comprehensive CFD solution comprises several components, including the high-order mesh generator and preprocessor HOPR, the solver Flexi itself, and a converter to the Paraview format for visualization and postprocessing tasks. Flexi's support for fully unstructured curved hexahedral meshes with non-conforming element interfaces enables users to handle complex geometries with ease. Moreover, its preprocessor HOPR facilitates the generation of curved meshes from various linear meshes obtained from both open-source and commercial grid generators.

Flexi's foundation on the highly efficient Discontinuous Galerkin Spectral Element Method enables users to achieve remarkable levels of accuracy, with simulations reaching orders as high as O(20) and beyond. Furthermore, the framework is designed to leverage modern parallel architectures to their fullest potential, allowing for production runs spanning over 100,000 cores. The solver, along with its input/output functionalities, scales efficiently to accommodate multiple hundred thousand cores. Additionally, the integrated toolchain supports parallel post-processing and visualization, ensuring seamless handling of large datasets. In summary, Flexi emerges as a versatile and user-friendly framework, capable of addressing a wide range of challenges in the realm of compressible flows while maintaining efficiency and scalability.