Dr. Gianluca Iaccarino

Stanford University

Automatic Grid Generation For Les In Complex Geometries

Orthogonal grids with local anisotropic adaptation are combined with an Immersed Boundary (IB) method and used to perform large eddy simulations. The approach used to generate meshes with desired normal and tangential resolution to three-dimensional surfaces is based on a ray tracing technique. Fast sorting algorithms, bounding-box intersection detection, alternating direction tree searches and grid-aligned ray casting are used to reduce the computational cost. In addition, an integer space mapping of the domain of interest is used to produce grids in any orthogonal coordinate systems, i.e. Cartesian and Cylindrical. Anisotropic refinement results in a considerable reduction in grid size while achieving user-specified resolution in any location within the domain. The resulting grid generation tool, has been developed in C++ and uses domain decomposition to achieve considerable parallel scalability.

The generated meshes consist of non-boundary-conformal hexahedrals with hanging nodes (orthogonal polyhedrals) and, therefore, require a fully unstructured discretization. The ASC Large Eddy Simulation solver CDP is applied to perform simulations of the cold flows in various combustor geometries. An IB treatment based on solution reconstruction is included to impose appropriate boundary conditions on the cell faces representing the actual boundaries; it has the property of ensuring local mass conservation and its accuracy is investigated for laminar and turbulent flows in channel not aligned with the grid. Mesh modifications that improve the grid quality for LES applications are also introduced.

Friday, April 28, 2006, at NOON
ETC 7.146

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