DLR-Project Digital-X: Next generation CFD solver 'Flucs'

Abstract

The development of DLR’s ‘next-generation’ flow solver was initiated as part of the project Digital-X to provide a basis for a consolidated flow solver using modern software techniques with high flexibility and high degree of innovation for a wide range of multidisciplinary applications. An overview of the design and development of the resulting flow solver Flucs (FLexible Unstructured CFD Software) is presented, its current status is described, and first results for internal and external flows are shown. The development followed a top-down approach identifying significant drivers in terms of application range and software design and was evaluated during the project to identify possible drawbacks in early stages and is continuously monitored to keep maintainability and expandability. The development is supported by modern software tools, such as distributed version control, web-based code reviews, and continuous integration. The kernel of the resulting design is a framework whose data structures and methods serve as a basis for implementing lean modules, for example equations, discretizations and time-integration methods. The framework provides basic functionalities like efficient implementation of loops, parallelization, or the provision of required data. Based on the framework, two discretizations are implemented: a second-order finite-volume discretization and a discontinuous Galerkin discretization with variable order, both of them using the same sets of implemented equations like the Euler-equations, the Navier-Stokes equations, or the RANS equations. A focus of the next-generation solver is its efficient use on current and future parallel HPC systems. The framework currently provides a two-level parallelization consisting of a domain decomposition that features communication/computation overlap, and shared-memory parallel processing of a domain. The simulation-setup layer of Flucs is designed as compatible Python API for the simulation environment FlowSimulator which provides a flexible interface to a wide range of multidisciplinary simulation-scenarios.