Fast and accurate simulations of air-cooled structures

There are fields of engineering for which the CAD-based Navier-Stokes solvers are too expensive; architecture and medicine for blood flows are two such examples. Mesh generation and adaptation is also a bottleneck because the users are not expected to have the know-how. We report here on a Navier-Stokes solver for incompressible temperature and time dependent flows dedicated to architectural applications. The building blocks are not new: a finite element method with time implicit pressure projection steps and mesh adaptativity; but putting them together in an easy to use and efficient 3D code is the challenge which motivates this paper. For non-engineering applications the user interface is a big problem. In an earlier attempt we designed freefem3D based on a fictitious domain discretization, thus avoiding boundary fitted mesh. However it turned out that the display of the solutions requires a boundary fitted mesh; it is possible to generate a feasible surface mesh for graphics but it is much more difficult to generate a feasible surface mesh for FEM. In this project the user interface is taken from freefem3d; then, with a marching cube algorithm we produce a graphic only feasible mesh; finally a surface mesh, adapted to a FEM computation is constructed with an adaptation module and the result is used as input to a Delaunay volumic mesh generator. The solver is optimized and parallelized, all modules are the authors' work. Three applications are presented, for which the data preparation takes less than a day and results are obtained overnight on a PC cluster. One of the application is presented in details; it is an air cooling system for a canister containing radio-nucleides. (c) 2005 Elsevier B.V.. All rights reserved.