Defining a Fluid Domain

You can define a fluid domain to specify the physical fluid to be simulated in a flow simulation, fluid-structure interaction (FSI) simulation, or conjugate heat transfer (CHT) simulation. You can define a fluid domain to model fluid flow that is contained within the structural part/model, such as water flowing through a pipe. You can also use it to model fluid flow around the structural part/model, such as air flowing over a plane's wing.

This task shows you how to:

Before you begin: For an FSI or CHT simulation, open your structural model in the modeling app. This approach lets you define the geometry of the fluid by using the geometry of the structure.

If you already have your fluid model contained in a part, open the part directly in the modeling app. Orphan meshes are also supported for modeling a fluid.

If your model is entirely solid geometry with no shell sections, no surfaces defined on part faces, and no orphan meshes, you can use the Model Setup dialog box to create the fluid domain and several other modeling components. Using this dialog box can save time by enabling you to define several modeling components at the same time. For more information, see Setting up the Model for Simulation.

See Also
About Fluid Domains
In Other Guides
Editing Simulation Features

Define a Fluid Domain Using Part Geometry Only

You can define a fluid domain whose boundaries are defined entirely by the structural parts in your simulation.

  1. From the Setup section of the action bar, click Fluid Domain .
  2. Optional: Enter a descriptive Name.
  3. Select the structural parts that either contain the fluid or are surrounded by the fluid flow.
    1. From the Parts section, click to add a part.
    2. Select the geometry supports in the model.
    3. Click OK.

      You can select an orphan mesh structure that is contained in the current finite element model (FEM) representation. The structural orphan mesh must be part of the same FEM representation as the hex-dominant mesh of the fluid domain. Mesh Groups cannot be used for the structural geometry.

  4. Optional: Select the surfaces that contain (or partially contain) the fluid.
    1. From the Surface Selections section, click to add a surface definition.
    2. Select the surfaces you want to include in the definition.
    3. Specify Regions to narrow the extent of the selected surfaces to a fluid region.
    4. Click OK.
  5. Click OK.

Define a Fluid Domain Using Part Geometry, Exterior Boundaries, and Subregions of the Structural Parts

You can define a fluid domain based on a part's geometry and other factors, such as bounding boxes, planes, or subregions of your structural parts. This method also requires you to specify the openings that are part of the fluid domain.

  1. From the Setup section of the action bar, click Fluid Domain .
  2. Optional: Enter a descriptive Name.
  3. Select the structural parts that either contain the fluid or are surrounded by the fluid flow.
    1. From the Parts section, click to add a part.
    2. Select the geometry supports in the model.

      You can select an orphan mesh structure that is contained in the current FEM representation. The structural orphan mesh must be part of the same FEM representation as the hex-dominant mesh of the fluid domain. Mesh Groups cannot be used for the structural geometry.

    3. Select Mesh conformally with fluid domain to mesh the part with the fluid domain, such that the mesh interface between them is conformal.

      Each part of the fluid domain for which you enable this option must have exactly one solid part as a support. In addition, if you select this option for at least one part, the app will not create boundary layers at all for the entire fluid domain.

      If you clear this option, the app uses the part's geometry as a boundary.

    4. Optional: Select Allow boundary layers to be added to enable creation of boundary layers along the part boundary.
    5. Optional: Select Mesh with surface wrap to mesh the part with a surface wrap.
    6. Optional: If you selected Mesh with surface wrap, select Visualize surface wrap to display the part with its surface wrap in the 3D area.
    7. If you selected Mesh with surface wrap, enter values for the Minimum size and the Maximum size, which are the minimum and maximum mesh sizes used to refine the mesh of the part.

      Using a maximum mesh size that is larger than the mesh size specified in the volume mesh yields better results.

    8. Click OK.
  4. Optional: Create exterior boundaries for the flow.

    Boundaries can restrict the fluid domain to a smaller subset of the interior of the structural model. They can also define the outer boundaries of the fluid. In the latter case, the bounding region contains the fluid that surrounds the structural model.

    1. From the Exterior Boundaries section, click to add an exterior boundary.
    2. From the Boundary type options, select one of the following:

      Option Description
      Bounding box Creates a bounding box by using the Cartesian coordinates that you specify. You can resize the bounding box by dragging its handles.
      Geometry Creates a 3D boundary by using existing surfaces in your model that you select.
      Planes Creates a bounding plane by using the Cartesian coordinates that you specify. You can define the bounding plane using the global coordinate system or a local coordinate system.

  5. Specify where the fluid flows.
    1. From the Regions section, click to add a region.
    2. Select one or more surfaces in the model as the geometry support.

      For internal flow simulations, you must select the surface of the cavity that contacts the fluid (for example, the inner wall of a pipe). In some simulations, this surface is where you later apply a wall boundary condition (for FSI simulations, you later apply a co-simulation.)

      For external flow simulations, you must select a surface around which the fluid flows. You can select a surface group to define this support.

      A glyph appears in the model to indicate the location of the fluid.
    3. Optional: Click Flip direction to switch the side of the surface that the fluid contacts.

      For example, the glyph in the image below indicates that the fluid is located inside the pipe.

  6. For flow through the interior of a model, select the openings through which the fluid flows.

    Specify the location of all openings, but do not differentiate between inlets and outlets. You add this information later when you define flow conditions as part of the scenario.

    1. From the Openings section, click to add an opening.
    2. Select a closed loop in the model as the geometry support.

      The image below shows an example of a closed loop.

      You can also select an edge group as this support.

      A circular disc glyph shows the location of the inlet or outlet opening.
    3. Repeat the previous steps to define the remaining openings in the model.

      For example, a car's exhaust manifold might have five openings (four inlets and one outlet).

  7. Optional: Select the surfaces that contain (or partially contain) the fluid.
    1. From the Surface Selections section, click to add a surface definition.
    2. Select the surfaces you want to include in the definition.
    3. Specify Regions to narrow the extent of the selected surface to a fluid region.
    4. Click OK.
  8. Click OK.