tg05 - SEDAN GEOMETRYVIRTUAL CLEANUP 5. SEDAN...

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SEDAN GEOMETRY—VIRTUAL CLEANUP © Fluent Inc., Sep-04 5-1 5. SEDAN GEOMETRY—VIRTUAL CLEANUP In this tutorial you will import an IGES file containing the geometry for a sedan automo- bile, clean up the geometry, and mesh it with triangles and tetrahedra. In this tutorial you will learn how to: Import an IGES file Specify the way in which the geometry will be colored Connect edges, using a manual and an automatic method Merge faces Create a triangular surface mesh Mesh a volume with a tetrahedral mesh Prepare the mesh to be read into FLUENT 5/6 5.1 Prerequisites This tutorial assumes you have worked through Tutorial 1 and, therefore, that you are familiar with the GAMBIT GUI.
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Problem Description SEDAN GEOMETRY—VIRTUAL CLEANUP 5-2 © Fluent Inc., Sep-04 5.2 Problem Description The problem to be considered is shown schematically in Figure 5-1; it is the external body of a luxury sedan. You will generate a mesh on the outside of the car body; therefore, you will create a brick around the sedan to represent the flow domain. Figure 5-1: Sedan geometry
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SEDAN GEOMETRY—VIRTUAL CLEANUP Strategy © Fluent Inc., Sep-04 5-3 5.3 Strategy In this tutorial, you will create a fully unstructured tetrahedral mesh around a car-body geometry imported as an IGES file. This tutorial illustrates the steps you would typically follow to prepare an imported CAD geometry for meshing. The imported geometry is “dirty”—that is, there are gaps between some of the surfaces that make it unsuitable for creating a CFD mesh. After examining the raw imported geometry to identify its problems, such as unconnected edges, you will clean up the geometry using the tools available in GAMBIT. Most of the gaps can be fixed automatically either during mesh import or subsequently by means of the “connect edge” command. The original CAD geometry is not modified during the fixing process; the modifications required to eliminate the gaps are made using “virtual” geometry, which lies on top of the “real” geometry. Some edges in the original geometry are very short and will be eliminated using the “vertex connect” command. Other edges are not automatically connected, because they are farther apart than the speci- fied tolerance. You will connect such edges manually. The imported geometry includes a number of small surfaces, the edges of which may unnecessarily constrain the mesh generation process. Using the “merge faces” command, GAMBIT allows you to easily combine these surfaces prior to meshing. You can then have GAMBIT automatically create a triangular mesh on the car body. Since the imported geometry consists only of the car body, you need to create a suitable domain around the car in order to conduct a CFD analysis (this is loosely equivalent to placing the car in a wind tunnel). The remainder of the tutorial shows how to add a real box around the car body, use virtual geometry to create some missing faces, and finally stitch all faces together into a single volume. This volume can then be meshed (without any decomposition) using a tetrahedral meshing scheme.
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This note was uploaded on 01/13/2011 for the course MECHANICAL ME:5208 taught by Professor P.k.lele during the Spring '10 term at Jadavpur University.

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tg05 - SEDAN GEOMETRYVIRTUAL CLEANUP 5. SEDAN...

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