Tetra meshing is not efficient for capturing shear or boundary layer physics. Using inflation elements (prism, penta-6 or hexa) along surfaces efficiently increases boundary layer resolution perpendicular to the wall, allowing you to capture these effects. With Ansys ICEM CFD, mixed prism and tetra generation is automatic and intelligent, creating prism layers near the surface while maintaining the ease and automation of Tetra mesh. Prism has always been necessary for CFD customers, but now that the feature is more widely available, many other branches of CAE have started using prisms to better resolve the physics perpendicular to the surfaces of their models.

To capture the Y+ for a Navier-Stokes mesh, the spacing of the prism layers is the primary concern, with the rate of volume change between cells also important. Calculations are done between nodes or elements, and a Prism mesh gives you more elements perpendicular to the surface. This is an efficient way to achieve better resolution (more calculations per unit distance) of the solution normal to the surface, without increasing the number of elements along the surface. This gives you a quicker and more accurate solution than can be achieved with a very fine tetra mesh.