Mesh Enhancement

Mesh Enhancement adds element layers along all fluid-wall and fluid-solid interfaces. It augments the original mesh to produce a smooth distribution along all walls, which is critical for accurate flow and temperature prediction. Mesh Enhancement ensures adequate mesh across small gaps, which can be very difficult manually.

Mesh Enhancement creates layers before the 3D mesh is constructed. Diagnostic algorithms detect and avoid element clashes in small gaps automatically. Element layer height across each surface is uniform, and is based on the smallest length scale on a surface. Gradual transitioning between surfaces ensures gradual variations in element height throughout the model.

Layer uniformity is important for accuracy in certain analyses. Examples include flows in which the turbulence is very sensitive to the flow near the walls and within long, narrow channels. In the latter case, meshes that have been enhanced have been shown to be significantly less disruptive than non-enhanced meshes to the flow near the walls, resulting in improved flow uniformity throughout the channel.

To open the Mesh Enhancement dialog, click Enhancement on either the Mesh Sizes quick edit dialog or in the Automatic Sizing context panel.

Enable mesh enhancement

Toggles Mesh Enhancement (on by default)

Automatic layer adaptation

Toggles automatic layer thickness adjustment that ensures proper layer height based on the turbulent law of the wall “y+” parameter. This is most useful for external aerodynamic studies.

Number of Layers

Controls the number of layers of prismatic elements. Up to five layers can be created. The default is three.

In some rotating-region analyses, reducing the number of layers to 1 improves solution stability.

Layer Factor

Controls the layer thickness. The layer height is determined by multiplying this factor by the local isotropic length scale for that surface. Reduce this factor for thinner layers and reduced total thickness.

Because Mesh Enhancement layers are constructed prior to the 3D mesh, changing certain analysis settings after the mesh has been generated will require the entire mesh to be regenerated. If the analysis is continued from a saved iteration or time-step, the results are mapped to the new mesh.

Changes to analysis settings that will cause the mesh to be regenerated include:

• Changing a material type. An example is changing a solid to a fluid. Changing a material but not its type (example: air to water) will not cause the model to re-mesh
• Adding or removing a flow boundary condition (such as velocity, pressure, volume flow rate, mass flow rate, external fan, slip, unknown, periodic, and external fan). Changing the value of an applied condition will not cause a re-mesh
• Adding or removing a motion assignment
• Modifying a boundary mesh enhancement parameter

An extension of Boundary Mesh Enhancement, Automatic Layer Adaptation is useful for high speed aerodynamic flows where the distance between the near-wall node and the wall-node is critical for accuracy. This is ideal for external flows such as vehicle aerodynamics and hydrodynamics, but is not so useful for slower speed internal flows.

To enable, check the Enhance Boundary Mesh and Automatic Layer Adaptation boxes.

After iteration 37, the Y+ values throughout the model are inspected at every iteration. The nodes nearest the walls are moved closer to drive the Y+ values within the optimum range for turbulent flow. There is only a slight time penalty for this adjustment scheme.

Automatic Layer Adaptation can be enabled any time during an analysis. Be sure to run the analysis for at least another 50 iterations after enabling it.