Optigrid: from Qualitative to Quantitative CFD

Patrick LAGACÉ, Isik OZCER, Guido BARUZZI, Vincent SOUMOY, Wagdi HABASHI





Generating an appropriate mesh for a CFD calculation is tedious and is part guesswork part experience. The mesh must be fine where appropriate and coarser in other areas. It is, however, difficult or impossible to do so before knowing the final solution. Even a good mesh for a specific geometry, at given flow conditions, may be inappropriate at other flow conditions.
NTI has developed a unique automatic mesh adaptation tool: OptiGrid.
OptiGrid dramatically shortens the task of meshing-by-guessing, and, as a bonus, makes your CFD code converge faster. After partially converging the solution on the initial mesh, OptiGrid assesses its quality, edge by edge, via an a posteriori error estimator based on minimizing the truncation error. It then systematically modifies the mesh to reduce and equalize the error throughout the domain. There is no regridding: OptiGrid moves nodes, refines, coarsens and swaps edges.
OptiGrid does not refine blindly in the three directions, but yields stretched meshes that significantly reduce the number of grid points, and capture with high resolution unidirectional CFD features such as shock waves, boundary layers, wakes, vortices and slip lines.
All operations being edge-based, OptiGrid can be coupled to any finite volume or finite element flow code that uses hybrid unstructured meshes composed of hexahedral, tetrahedral, prismatic and pyramidal elements.
The total computational time needed for solver + adaptation can be lower than that of the solver on an initial much finer mesh.
An automatic “CAD reconstruction” component makes the process independent of format (or availability) of the original CAD file. All surface mesh adaptation operations performed by OptiGrid respect the reconstructed CAD, preserving or improving the curvature throughout the operations.
OptiGrid will be demonstrated for very complex situations.
It is time for you to move from qualitative CFD to truly quantitative CFD

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