One example of where passive cells can occur is in the background mesh where the overset mesh cells are used in the assembled mesh. Cells where the flow equations are not solved are called “passive”. When a cell is receiving data it is named “acceptor” and when it is providing data it is called “donor”. Acceptor cells are present in both meshes. These cells are transferring data between the background and overset mesh. Active cells are present in both the background and overset mesh. It is in these cells which the flow equations are solved. There is a colour coding in the picture to describe which cells transferring flow field information: In the picutre above you can see the regions descretized by the background mesh, overset mesh and also the mesh which will be used by the simulation – the assembled mesh (displayed with light blue colour in the picture). One example where overset mesh comes in handy is when simulating a football moving through air, as in the picture below. The background mesh is usually quite coarse while the overset mesh is refined, since the moving object may need a customized refined mesh to predict the more complex flow field around it. Usually one mesh is describing the whole computational domain (background mesh), and the other mesh is describing the mesh for a smaller part of the domain which is moving with an moving object (overset mesh). Overset mesh is a method using (at least) two different computational grids, and allowing the grids to overlap and transfer flow field information between the grids. This week at the Volupe blog we will look into the exciting area of overset meshes.
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