Setting Up Walls and Other Boundaries

After the setup of inflow and outflow boundaries, you specify the wall, symmetry plane, and axis boundaries to finalize the confinement of the fluid domain.

To set up a wall, symmetry plane, or axis boundary:
  1. Select the Regions > [region] > Boundaries > [boundary] node and set Type to one of the following:
    • Wall—this is the default boundary type. It represents an impermeable surface. You can apply slip, no-slip, or partial-slip conditions to a wall.
    • Symmetry Plane—set this boundary type along a plane of geometrical and flow symmetry to reduce the size of the solution domain. You can also use the symmetry plane boundary as a planar slip wall due to the shear stress being zero.
    • Axis (only available with the Axisymmetric space model)—set this boundary type to define an axis of rotation for two-dimensional axisymmetric flows. The axis must lie on the X-axis.

    For more information, see the specific topics in the Theory Guide under Boundary Conditions.

  2. Expand the [boundary] node and, depending on the selected boundary type, do one of the following:
    Boundary Types Steps
    Wall
    1. To define how the wall surface acts on the fluid passing across it, select the Physics Conditions > Shear Stress Specification node and set Method to one of the following:
      • No-Slip—with this method, the fluid sticks to the wall and moves with the same velocity as the wall. Thus, for a stationary wall, the fluid has zero velocity at the wall. Default method.
      • Slip—select this method when you want to represent an impenetrable but traction-free surface.
      • Specified-Shear (only for laminar flows)—set this method in situations where there is some degree of slippage between the fluid and the wall, such as for polymer/rubber flow simulations or hydrophobic/hydrophilic fluid flow simulations. You set the wall shear force using the Physcs Values > Wall Shear Force node.
    2. For simulations that use the Maxwell Slip model, select the Physics Conditions > Shear Stress Specification node and set Method to Partial-Slip. This applies the Maxwell Slip model to the selected wall boundary.

    For more information, see Viscous Regime Models Reference—Wall Boundary Settings and Partial Slip Models Reference.
    Symmetry Plane Select the Regions > [region] > Boundaries > [boundary] node and set Type to Symmetry Plane.
    Axis Select the Regions > [region] > Boundaries > [boundary] node and set Type to Axis.