The conformal adaption process does not create hanging nodes. Instead, all the cells sharing an edge or face include all the nodes on those entities. The conformal refinement process adds nodes on edges and the conformal coarsening removes nodes and retriangulates the resulting cavity.
To refine the cell, split the boundary or internal faces (including periodic boundary faces). This technique has two primary advantages:
Figure 26.2.4 shows how the triangle labeled would be split for refinement. The cells are refined by splitting the longest edge of the triangle or tetrahedron.
The process is to find the longest edge of any cell marked for refinement search for a longer edge. If any of the neighbor cells has a longer edge, the scheme spins around that new edge searching for a longer edge. When the longest edge is identified, it is split. Although this process maintains the quality of the triangulation with repeated application, it splits many cells that are not marked for refinement.
For example, Figure 26.2.5 shows the original cell marked for refinement (marked with an X), and Figure 26.2.6 shows the final mesh created by the conformal refinement process.
The grid is coarsened by removing nodes that are shared by cells marked for coarsening. If all the cells attached to the node are marked for coarsening, the solver attempts to remove the node. Local retriangulation process is attempted for each of the nodes marked for removal, as follows:
Figure 26.2.7 illustrates the removal of node and the resulting retriangulation. In this example, and are the cells attached to the node. Faces and are the faces inside the cavity. Faces on the cavity includes and . The new faces of the triangulation are and , and the new cells are and .
Nodes introduced by refinement are called refinement nodes. Nodes that existed in the mesh before refinement are called original nodes. By default, only refinement nodes can be removed in the coarsening process, but you can remove any node by resetting the node flags. For information on node flags, see Section 26.12.
Presently, the grid-coarsening facility is available only in the 2D version of FLUENT.