Anisotropic Meshing for Lifting Surfaces

Anisotropic meshing allows you to generate a surface mesh that contains stretched quad elements aligned with features (anisotropic faces). By using stretched elements, you can reduce the number of faces in the mesh while retaining geometrical and solution accuracy.

When meshing aerospace geometries such as wings, propeller blades, or turbine blades, you are required to generate a fine mesh that adequately captures the curvature of the leading and trailing edges. In general, you want the mesh to be aligned to the leading and trailing edges and to be stretched in the spanwise direction (with short edges in the streamwise direction). To help reduce the cell count while maintaining solution accuracy, you can apply anisotropic meshing to these edges. It is computationally less expensive to use anisotropic mesh in comparison to isotropic.

The example below shows the difference between two meshes: isotropic and anisotropic. Both of them have the Surface Remesher, Polyhedral and Advancing Layer Mesher.

In order to use the anisotropic meshing option, your volume mesh must be based on an initial quadrilateral surface mesh. Before using anisotropic meshing, make sure that you have part curves along the leading and trailing edges of the wing, and that the starting geometry represents the fluid.

  1. Right-click the Geometry > Operations node and select New > Automated Mesh Operation.
  2. In the Create Automated Mesh Operation dialog:
    1. Set Parts to the part which represents the fluid volume.
    2. Select the Surface Mesher and choose one of the following core volume meshers:
      • Polyhedral Mesher
      • Tetrahedral Mesher
      NoteYou can only generate anisotropic quadrilateral surface meshes with the Advancing Layer Mesher and Directed Mesher.
    3. Click OK.
Anisotropic layers are created only on quad surfaces. In order to create anisotropic layers, you must make sure that the Meshing Method is set to Quad Dominant as otherwise Simcenter STAR-CCM+ cannot create the layers and a warning message is printed in the output window to inform you.
  1. Select the Meshers > Surface Remesher node and set Meshing Method to Quad Dominant.
  2. Expand the Automated Mesh > Default Controls node and set the parameters that you require for the overall fluid domain.
  3. Right-click the Automated Mesh > Custom Controls node and select New > Curve Control.
  4. Select the Curve Control node and in the Properties window:
    1. Ensure that Enable Control is activated.
    2. Specify the Part Curves on which the anisotropic meshing should be applied. For a wing or blade, these are typically the leading and trailing edges.
  5. Select the Custom Controls > Curve Control > Controls > Anisotropic Surface Size node and activate Specify anisotropic surface size settings.
  6. Under the Values node, set the Growth Ratio, Maximum Aspect Ratio, Number of Constant Layers, and First Layer Thickness to values that suit your scenario.
    For more information, see Curve Controls and Values.
  7. To generate a good quality mesh where two opposite part curves are connected together in a cusp:
    1. Select the Custom Controls > Curve Control > Controls > Anisotropic Surface Size node and activate Specify anisotropic mesh distribution between close Part Curves.
    2. Under the Values node, set the Minimum Layer Size in Narrow Regions of Thin Areas and the Minimum Number of Layers to values that suit your scenario.
    For more information, see Curve Controls and Values.
    The image below shows two examples with the same First Layer Thickness value. The first example on the left displays a mesh where the Specify anisotropic mesh distribution between close Part Curves option is deactivated. The second example on the right shows a mesh where the option is activated and the Minimum Number of Layers is set to 3 and the Minimum Layer Size in Narrow Regions of Thin Areas value is set to a small value.

Anisotropic boundary layers grow from the part curve as long as the first layer thickness is smaller than the target size of the surface in that specific location. The target size for the surface determines the width of cell faces along the length of the part curve. Hence, by choosing the target size and first layer thickness correctly, you can achieve the stretched faces along the spanwise direction. For cases where the target size is smaller than the anisotropic first layer thickness, the mesh does not generate any anisotropic boundary layer.

One of the best practices is to deactivate Perform Curvature Refinement and Perform Proximity Refinement. By disabling the curvature and proximity controls, the mesh is refined using only the anisotropic size control applied on the part curves, as shown in the image below.

When anisotropic meshing is enabled on a curve, the surface remesher generates a number of face layers (n) of fixed size, normal to the curve. Starting from n+1, the anisotropic layers grow in size with a ratio equal to the growth ratio until the anisotropic size of the layers are the same as the isotropic size (target size) of the surface in that position.

  1. Execute the Automated Mesh Operation.
  2. Create a scene to visualize the mesh. See Mesh Visualization.
The example below shows how anisotropic meshing works.
Suppose we have a uniform size surface with a Base Size of 0.05 m and a part curve CA that has First Layer Thickness of 0.005 m. For this example, the anisotropic layers are created on CA since the first layer thickness is smaller than the base size. The image below shows that anisotropic layers are created along the edge.

In another example, suppose we have a uniform size surface with a Base Size of 0.05 m and a part curve CB that has First Layer Thickness of 0.1 m. For this example, anisotropic layers are not created for CB since the base size is smaller than the first layer thickness. The image below shows that anisotropic layers are not created along the edge.