Meshing techniques
Grid generation is a crucial problem for the computation of complex aircraft configurations using a body fitted structured code. Furthermore, due to the data management of structured grids, a local refinement will be propagated through the whole grid even in zones where gradients are expected to be low. This can lead to very large grids, especially for complex geometries. Two approaches permit to reduce this drawback: i) conservative patched grid, ii) automatic mesh refinement.
Conservative Patched Grid (CPG)
The purpose is to develop an efficient way to simplify the grid generation and to deal complex configurations using moderately sized grids. The approach which has been chosen to use NSMB on meshes having no coincident interfaces. For this kind of meshes, blocks must have common interfaces but do not need the same location of grid nodes. This approach avoids the mesh propagation from a block to another block The flexibility of this kind of mesh allows mesh refinement and makes it easier to cluster grid points. A 3-D conservative patched grid algorithm using Jameson centered scheme has been implemented in NSMB. Various test cases have been run to check the conservativity of the algorithm. The efficiency of the method has been demonstrated on complex geometries such as AS28G and a fighter forebody including optronic systems and the feeder (see Fig).
Flow simulation around a fighter perturbed by the optronic system and the feeder.
Application of the conservative patched-grid technique.
Automatic Mesh Refinement (AMR)
Another approach is to use the Automatic Mesh Refinement concept. It consists in splitting a cluster of grid cells in a zone of high gradients and to automatically join these cells in new blocks. The activity on AMR has increased in 1999. A verification on the previously coded AMR by AM-Airbus is underway. In the next phase, extension to other schemes than central is planned.
