Boundary Layer Exposed Ratio Flag

Boundary layer exposed ratio flag sets the height-to-length exposed aspect ratio for boundary layer elements.

When this flag is enabled, a default value of 0.2 is set for the Boundary layer exposed ratio.

If the boundary layer does not conform to the model boundary, such as in the case of a free edge of a non-manifold model face or if the dihedral angle between a BL face/non-BL face interface exceeds the conformity angle, then the side of the boundary layer mesh is exposed to the volume mesher. In typical Reynolds-Averaged Navier-Stokes (RANS) meshes, the aspect ratio of side mesh faces of the boundary layer can be extremely high. In these situations, the exposed mesh faces result in poor local mesh quality of the surrounding isotropic mesh. Thus it is desirable to prune the exposed mesh and essentially "hide" the boundary layer anisotropy. Setting the Boundary layer exposed ratio to zero effectively disables the control since all valid face elements have a boundary layer exposed ratio > 0. The performance of the isotropic volume mesher may become quite poor if the boundary layer exposed ratio is set < 0.2 where many highly-anisotropic faces are exposed to the volume mesher.