Meshing Around a Rotational Axis

When you mesh around an axis using a rotational sweep, the mesher creates high-valence vertices on the axis—that is, vertices on which a high number of edges meet. The resulting thin cells affect the convergence and robustness of the physics solvers that use the mesh. Rotational sweep mesh coarsening avoids these thin cells by successively merging cells in the radial direction as the mesh approaches the central axis. Merging occurs across transitions, which are defined as virtual interfaces in the azimuthal direction across which two or more cells are merged into a single cell. The transition distance is the radial distance of a transition from the rotational axis. The mesher can either make transitions automatically based on a target aspect ratio, or else apply transitions that you define manually.

Rotational sweep coarsening can be used for applications such as a diesel in-cylinder combustion simulation. The following image shows a geometry without and with the coarsening:

注	If both Internal Surfaces and Rotational sweep coarsening options are activated, then internal surfaces will not be generated.

To activate the rotational sweep coarsening feature:

Select the Directed Mesh node and activate Rotational sweep coarsening.
A new node Rotational Sweep Coarsening appears under the Directed Mesh operation.
Right-click the Rotational Sweep Coarsening node and choose New Mesh Coarsening.
Select the Rotational Sweep Coarsening > Mesh Coarsening node, set Transition Controls to one of the following options:
- Use Default
  The number of coarseness transitions and the distance from the rotational axis where the transitions occurs are determined automatically based on the Aspect Ratio.
- Specify Custom
  Allows you to create one or more transitions that define where coarsening occurs. The image below shows an example of three coarsening transitions:

To create one or more transitions when Specify Custom is selected:

Right-click Rotational Sweep Coarsening > Mesh Coarsening > Coarsening node and select New Transition.
This creates a new Transition node under Coarsening Transitions.
To specify the transition properties:
1. Select the Coarsening Transitions > Transition node.
2. In the Properties window, select Distance from Rotational axis option and set the distance at which the transition occurs.
3. Select the Merge ratio 1: to specify the number of cells to merge across the transition.

The following image shows the mesh quality of an engine geometry when the rotational sweep coarsening is activated using three coarsening transitions.