If you need to simulate an accurate transient including a rotating device (like a fan or a propeller), the Sliding Interface approach offers a simple and very effective option to handle Mesh Motion. The following guidelines will help you to get the maximum accuracy across the Interface, reducing to the minimum the pressure disturbances associated with the discontinuity of the mesh.

Please ensure to follow thoroughly all the points below in particular if you see remainder faces out of the interface, or high pressure disturbances at the Interface as in picture below:
 

In the following, we will consider as target application a classical fan or propeller Simulation, in which Rigid Body Motion is used to impose the rotation of the device, together with the cylindrical Region surrounding it.
 

1 – Set the Direct Intersector to Topology-Based Interfaces

The choice of the Direct Intersector option to Topology-Based is important to get maximum accuracy and parallel performance. The method is set for all the Interfaces of the model in the parent node “Interfaces”.
 

 

2 – Activate the option “Close Adjacent Cells”

The default setup may leave some open cells during the intersection process, which are usually not problematic for basic resolution of the fluid-dynamics across the Interface. However, when looking for accurate transient solutions, it is fundamental to activate the option “Close Adjacent Cells” in the properties of the Sliding Interface:
 

3 – Use a single Boundary and take advantage of the “Match Outer Perimeter” option

Former best practices may have suggested you to split the cylindrical surface of the rotating Region into three different Boundaries (the two flat circular bases and the lateral surface). With Topology-Based Interfaces this is no longer needed, nor recommended.
You are suggested to use just one single Boundary for the whole sliding interface, containing all the surfaces of the cylinder, and then use the option “Match Outer Perimeter” in the properties of the Intersection node of the Interface:
 

The above step is expected to ensure that 100% of the original Boundary faces will be properly transferred to the Interface. With this setup featuring Topology-Based Interfaces with Match Outer Perimeter, you are no longer required to check the percentage of intersected faces during the rotation of the inner Region, as it is expected to be always 100%.
 

4 – Ensure the same surface is used on both sides of the Interface

For the Sliding Interface to work properly, the faces must slide on the very same surface, namely a cylindrical one with a specified radius. You must ensure to be using the same radius (preferably exactly the same surface) on both sides of the Interface. This means that your meshing Pipeline should feature some Boolean operations defining the fixed and rotating domains starting from the same cylindrical surface.
 

5 – Use a CAD surface for the cylinder and ensure to mesh both sides with the same (uniform) size

Using a CAD is the most convenient way to ensure that the vertices of the Surface Mesh lay exactly on the cylindrical surface. To get accurate results, you are recommended to use the same mesh size on both sides of the Interface, and that such size is uniform over all the interface:
 

You are advised to check the outcome of Surface Remesher, since the mesh size you prescribed may be accidentally changed by other Custom Controls or by the action of Surface Proximity refinements.
Aligned Meshing is recommended, as it generates a very regular surface mesh pattern on the lateral surface of the cylinder:
 

6 – Prescribe a single (thick) prismatic layer on each side of the Interface

The Sliding Interface is an Internal interface, thus there is no need to generate a Prism Layer to capture any fluid-dynamic boundary layer. However, to get higher mesh quality in association with the Interface intersection, you are advised to prescribe 1 layer of prisms on each side of the Interface, the thickness being about half the local surface mesh size. The outcome should look like:
 

7 – Use a Time Step consistent with the mesh size on the Interface

The choice of the Time Step is dictated by several factors. Among these factors, you must also consider the mesh size at the Sliding Interface. Depending on the rotation rate, you can evaluate a “Courant Number” associated with the Sliding Interface Mesh Motion, which should be less than one (probably best less than 0.5). This means that in a Time Step, the mesh should slide of less than the size of a face.

Finally, in case you are using a constant value for the Time Step, you are advised to choose it such that it divides in an integer way the period of revolution of the fan/propeller. This way, after N Time Step, the 360 deg revolution is completed and the mesh will be again in the original position.

8 – ONLY FOR OLDER VERSIONS (prior to v19.02) – Set the Interface Orientation such that Boundary-0 corresponds to the Boundary of the rotating Region

To get the most accurate solution across the Sliding Interface, you are advised to use versions of Simcenter STAR-CCM+ v19.02 or higher. Up to v18.06, the Sliding Interface turned out not to be symmetric with respect to the involved Boundaries. In case you are forced to work with an older release, you are advised to set Boundary-0 to the Boundary belonging to the rotating Region:
 

Note that in most circumstances the Interface is generated automatically during the “Assign Parts to Regions” step. To revert the orientation of the Interface, right click on it and select “Reverse Orientation”.