The approach is to compute or for boundary cells on the specified viscous wall zones, define the minimum and maximum allowable or , and mark and/or adapt the appropriate cells. Cells with or values below the minimum allowable threshold will be marked for coarsening and cells with or values above the maximum allowable threshold will be marked for refinement (unless coarsening or refinement has been disabled).
Figure 26.9.1 shows the mesh for a duct flow, where the top boundary is the wall and the bottom boundary is the symmetry plane. After an initial solution, it was determined that values of the cells on the wall boundary were too large, and adaption was used to refine them. The resulting mesh is shown in Figure 26.9.2. This figure shows that the height of the cells along the wall boundary has been reduced during the refinement process. However, the cell-size distribution on the wall after refinement is much less uniform than in the original mesh, which is an adverse effect of adaption.
See Section 12.11 for guidelines on recommended values of or for different near-wall treatments.