Preparing Geometry for Moving Reference Frame

The geometry of the model must be prepared in order to distinguish the moving portions of the geometry from the static portions.

Before completing this procedure, make sure that you have a geometry part that represents the fluid volume. If necessary, extract the fluid volume from any surrounding solids.

The following image shows an example of a geometry suitable use with a rotational moving reference frame:



Creating a region for the rotating part

In order to split the initial fluid volume into a static and rotating part, you first create an additional volume shape that encloses the rotating part. With this additional shape, you can split out the part to which you later assign the rotating reference frame.

  1. To create a cylinder shape part, for example:
    1. Right-click the Geometry > Parts node and select New Shape Part > Cylinder and place it around the rotating object.
  2. To ensure that the rotating region has separate upstream and downstream surfaces, you split the surfaces of the shape part:
    1. Right-click Geometry > Parts > Cylinder > Surfaces > Cylinder Surface and select Split by angle.
    2. Rename the surfaces of the cylinder to [upstream] and [downstream] depending on the direction of the flow. When you assign the parts to regions, these surfaces form interfaces between the static and rotating regions. See the following image:
Through a series of boolean operations, you can define and split a rotating part from the static part. Be sure to perform each operation in the sequence provided and execute them separately.
  1. To split out a rotating region from the existing fluid volume, carry out the following steps:
    1. Intersect Operations - creates a part from the common volume of the selected parts.
      • Right-click Geometry > Operations and select New > Boolean > Intersect.
      • Select the Fluid_Volume and Cylinder parts.
      • Activate Perform CAD Boolean.
      • Execute the operation and rename the output part to Fluid_Rotate.
    2. Subtract Operations - removes the rotating region from the fluid volume.
      • Right-click Geometry > Operations and select New > Boolean > Subtract.
      • Select the Fluid_Volume and Cylinder as the input parts.
      • Set the Fluid_Volume as the target part and activate Perform CAD Boolean.
      • Execute the operation and rename the output part to Fluid_Static.
    3. Imprint Operation - generates necessary contacts between adjacent part surfaces.
      • Right-click Geometry > Operations and select New > Boolean > Imprint.
      • Select the Fluid_Rotate and Fluid_Static for the input parts and activate Perform CAD Boolean.
      • Right-click Operations > Imprint and select Execute
      The following image shows the rotating and static parts of the geometry.

  2. Assign parts to regions as follows:
    1. Within Geometry > Parts, multi-select the Fluid_Rotate and Fluid_Static nodes.
    2. Right-click on the selected parts and click Assign Parts to Regions.
    3. In the Assign Parts to Regions dialog, select the following options to define the parts to their regions so that the boundary conditions can be assigned.
      • Create a Region for Each Part
      • Create a Boundary for Each Part Surfaces
    4. Click Apply and then Close.
    Two new regions are created within the Region node. The Interfaces node also appears in the tree.

Continue to define and apply the reference frame.