Setting up Overset Mesh with Fluid Film

For certain applications, it is useful to combine overset mesh with fluid film.

Examples of such applications are:

  • automotive window wipers
  • fuel flow on an engine cylinder with a moving piston

You can now model a fluid film shell region passing from one overset region to another or to a background region.

For the combination of overset mesh with liquid film, the following requirements apply:

  • The overset model must be set up in a sliding configuration, that is, a boundary of the overset region must coincide with a boundary of the background region.
  • You must create the shell regions on the sliding boundaries of the overset region and the background region.
  • Each overset interface for shell regions must have a corresponding three-dimensional overset interface.
Before you begin to set up overset mesh with fluid film, generate a suitable mesh considering these requirements. In addition, the size of volume cells adjacent to the fluid film must be consistent for the background and the overset region. The following diagram shows an example:

The small cube is modeled as the overset region (red) and slides along the side wall of the large cube, which is modeled as the background region (grey). The fluid forms over the entire side wall of the background region, which coincides with the sliding wall of the overset region. You create two shell regions for the fluid film: one on the sliding wall of the red cube and one on the side wall of the grey cube. By creating an overset interface between the two shell regions, the fluid film can pass from one shell region to the other.

To set up overset mesh with fluid film:

  1. Set up the fluid film model.

    See Setting Up a Fluid Film Simulation.

  2. Set up the shell regions for the fluid film model. You must create one shell region on a boundary of the background region and one shell region on a boundary of the overset region.
    Fluid-Film interfaces and edges of the imprinted sliding overset boundary are created automatically as part of this process.

  3. Set the boundary type of the imprinted sliding overset boundary edges to Overset:
    1. Select the Regions > [Overset Shell Region shell] > Boundaries > [Overset Boundary edges] node and set Type to Overset Mesh.

  4. Set up the overset mesh boundary on the overset region.

    See Setting up Overset Regions

  5. In the overset region, select the sliding boundary and set its Type to match that of the contacting boundary within the background region. Usually, this boundary is a wall boundary.

  6. Select the Regions > [Overset Shell Region shell] > Boundaries > [Overset Sliding Wall] > Physics Conditions > Reference Frame Specificiation node and set Option to Lab Frame.
  7. Create the overset mesh interface between the background and the overset regions.

    See Overset Hierarchy and Overset Interfaces.

Note Currently, overset mesh with fluid film is not compatible with zero gap interface creation.
  1. Create an overset interface between the fluid film shell regions of the background region and of the overset region.
    1. Multi-select the shell regions of the background region and of the overset region.
    2. Right-click on any of the highlighted items and select Create Overset Mesh Interface.

The fluid film can now pass from the shell region on the background region to the shell region on the overset region and vice versa.