Rotational Sweep Coarsening And Volume Mesh Patterns In Simcenter STAR-CCM+

The Directed Mesher in Simcenter STAR-CCM+ can be a very useful and efficient tool for creating high-quality meshes on axisymmetric models. Typically though, there is a limitation in its use for models with large radial differences between inner and outer guide surfaces, or even non-hollow volumes where there is no guiding surface at all on the inner radius. In this week’s blog post we will show how you can make use of the Rotational Sweep Coarsening feature to overcome such hurdles. Moreover, we will show how you can use Volume Mesh Patterns to generate sweep meshes for fully cylindrical volumes.

Sweep meshing a quarter disc

Our example to showcase the Rotational Sweep Coarsening feature will be a quarter of a simple disc shaped model. The quarter disc is meshed with the Directed Mesher, sweeping from xz-plane to the yz-plane (i.e. clockwise direction). As the disc is continuous (i.e. non-hollow) and has no inner radius, the innermost cells will all coincide as we approach the center axis, creating infinitely thin needle cells (see picture below).

These cells will be of low quality and are deemed to cause problems in a simulation. This is where the Rotational Sweep Coarsening comes into play. The feature can be activated in the properties for the Directed Mesher (see below).

Once activated, additional options for the feature appear in a separate folder inside the Directed Mesher operation. The Default transition control determines the transition location based entirely on aspect ratio, but you can also specify a customized transition to explicitly determine where transition should occur.

Applying the settings shown above to the quarter disc generates a mesh like the one shown below. You can see that we have gotten rid of the needle cells close to the center axis.

Sweep meshing a complete disc

The Directed Mesher requires a source and a target surface for sweeping a mesh. This poses a limitation when it comes to sweeping a 360-degree body, since the source and target will be the same surface (which is not a viable option). There is however a workaround if you wish to use the Directed Mesher for a full 360-degree sweep – namely Volume Mesh Patterns. With this feature, you can use the Directed Mesher to sweep mesh parts of an axisymmetric body and then add copies of that mesh to complete the full revolution. We will now go through how to achieve this.

The starting point in our example is the quarter disc discussed above. The next step is to create a Circular Pattern. This is an operation found under the Surface Preparation category (see below).

In this case, our basis is a quarter disc, so we need four copies in total to create a full revolution. Moreover, the circular pattern should be distributed around the z-axis. These settings are given in the properties for the Circular Pattern operation (as shown below). You may note the Output Parts field, indicating that the operation will output three new parts. These parts will be copies of the original part, each with an angular offset of 90 degrees.

The next step is to create a Volume Mesh Pattern b ased on the newly created parts. This is to repeat also the volume mesh along with the defined pattern (rather than just the parts/surfaces). This operation can be found in the Mesh category of the geometry operations (see below).

As already mentioned, the input to this operation is simply the newly created parts from the Circular Pattern operation.

Finally, the new parts also need to be included in the region (as shown below).

Once all operations are executed, we will have a sweep mesh of a 360-degree revolution.

I hope this blog post has been informative. If you want to learn more about the directed mesher or rotational symmetry in STAR-CCM+, there are some previous blog posts on these topics as well: