To generate any CFD mesh, object-defining nodes are first created, then a surface mesh is generated from the nodes, then finally a volume mesh is generated from the surface. Mesh-generation software developed by the T*AFSM was used in this project to accomplish each of these three steps. In particular, ModelG, Surface95, and DimensionMG were used.
An additional problem in generating the CFD mesh for this project was that the desired geometry for the parachute had been generated already, during the SD simulation. The SD simulation had been conducted using a nine-noded surface mesh, not a three-noded surface mesh as would be generated by Surface95 and as we would want to use for the CFD simulation.
The procedure used to convert the nine-noded surface mesh to a three-noded mesh was to create a three-noded flat mesh of the cross parachute with geometry identical to that of the undeformed nine-noded mesh, then to project, using shape functions, the nodes of the three-noded mesh onto the deformed geometry of the nine-noded mesh. This was accomplished using a MATLAB script developed by Tim Bretl.
An example of a resulting mesh is shown below. This mesh contains 82142 nodes and 488425 elements. It was the mesh most often used in simulations, having enough refinement to give good results while being coarse enough to limit required computing time. Only the surfaces of the mesh (including the refinement surface, which is the irregularly shaped box appearing directly behind the cross-parachute) are shown, since the volume mesh elements are difficult to visualize in three dimensions due to their huge number.
Important in ensuring the accuracy of the simulation is that the surface of the cross parachute is duplicately defined in the CFD mesh. In other words, tetrahedral elements exist both "above" and "below" the cross parachute, matching triangular faces on the surface. This allows the flow conditions to differ from one side of the parachute to the other, as one would expect.
Also shown is a cross section of the interior volume mesh . The refinement regions included in the surface mesh definition result in a much greater volume mesh refinement on the surface of and in the wake area of the parachute, where the greatest flow detail will be present.
Resulting CFD Mesh, Surfaces Only
Resulting CFD Mesh, Cross Section of Interior Volume