Define the Fluid Model

Create the fluid domain, apply a material to it, and define the region where the flow occurs.

A fluid domain is a finite volume consisting of one or more fluid regions that are bounded by parts, exterior geometries, and openings. For external fluid flow simulations, you must define exterior geometry to cap the total space that you mesh. If your model is symmetric, you can use techniques while creating the fluid domain to reduce the amount of space that you need to mesh. This approach can significantly reduce the simulation's run time.

In this example, you create a fluid domain inside the duct part. You bound the fluid domain using the inlet and the outlet (both of which are openings). Then, you define the space inside the duct as the fluid region. The fluid region is where air flows through the duct.

  1. From the Assistant, click Model.
    The Finite Element Model dialog box appears.
  2. From the Model options, select Create to create a FEM.
  3. Name it DuctFlow_Mesh, and click OK.
    DuctFlow_Mesh A.1 appears in the tree.
    Tip: Press F3 to display the tree if it is not visible.
  4. From the Model section of the Assistant, click Model Setup .
  5. Apply the material definition for air to the fluid section associated with the fluid domain.
    1. Click to open the Material Palette.
    2. From the Material Palette, search for MynameEXAMPLE-Air.
      The Myname prefix is the duplication string you specified during Create the Fluid Simulation.
    3. Select MynameEXAMPLE-Air, and click OK.
      The app applies the material definition to the fluid section and closes the Material Palette.
  6. Expand the Fluid domain bounding parts section, and confirm that the duct part is selected.
  7. Select the region that contacts the fluid.
    1. Expand the Regions section.
    2. Select a surface inside the duct.
      A glyph of a blue cube with a stem appears on that surface.
    3. Select or clear Flip direction to ensure that the cubical portion of the glyph is immersed in what would be the fluid volume.
  8. Define the openings that allow fluid to flow through the duct.
    1. Click in the Openings section.
    2. From the context toolbar, select Edge Propagation .
    3. Select an edge on the inner side of the duct opening on the left.
    4. Enter 30deg in the pop-up window, and click Propagate.

      The app highlights all of the edges that comprise the duct's opening.
    5. Define the second duct opening in the same manner.
  9. Expand the Mesh section, and accept the default mesh density for the fluid interior and fluid walls.

    You customize these settings later in this example.

  10. Click OK.
    Three new items appear in the tree:
    • Physical Environment.1 appears underneath the Abstractions node.
    • Fluid Section.1 appears underneath the Properties node.
    • Hex Mesh.1 appears under the Nodes and Elements node.