The engineering of multiblock/multigrid software for Navier-Stokes flows on structured meshes

The paper describes EURANUS—a general software software system for the simulation of 3-D Reynolds-averaged Navier-Stokes flows about complex geometries, being developed for the European Space Agency for use as a major tool in its aerothermodynamic design work. The paper emphasizes the software engineering aspects of creating a general multiblock/multigrid solver. A geographically-distributed team of programmers are constructing the system with the idea that it should be a highly ordered and comprehensible platform upon which new formulations and methods can be incorporated in the future by people who did not participate in writing the original code. Presently, the software treats either perfect gases or air in chemical equilibrium. Closure of the Reynolds stresses is provided by either the Baldwin-Lomax turbulence model, or the κ-ϵ model. The key to a successful multiblock code, particularly if it is to serve as an evolving platform, lies in the design of a suitable data structure and a concept for the management of the data. With such a data structure we have designed a general framework of modular coding that incorporates various spatial discretization schemes based on either central or upwind differencing and either explicit of implicit time integration. Residual averaging and a multigrid technique accelerate the convergence to steady state. Two computed examples of viscous laminar hypersonic flow around the HERMES spaceplane provide an initial demonstration of the code.