The Interior Wall node adds a wall boundary condition on interior boundaries. It is similar to the Wall boundary condition available on exterior boundaries except that it applies on both sides of an interior boundary. It allows discontinuities of the dependent variables across the boundary. The Interior Wall node specifies no flux for the dispersed phase.

Select a Mixture boundary condition — No slip (the default) or Slip.

No slip is the default boundary condition for the mixture. A no slip wall is a wall where the mixture velocity relative to the wall velocity is zero. For a interior stationary wall, it sets the mixture velocity to zero at the wall:

For turbulent flows, the no slip condition may either be prescribed exactly or modeled using automatic wall treatment or wall functions depending on the Wall Treatment setting in the Turbulence section of the interface settings.

When Wall functions are selected, the Apply wall roughness option becomes available. Click to select the Apply wall roughness check box to apply the roughness correction. When the check box is selected, the default Roughness model is Sand roughness, which is derived from the experiments by Nikuradse. Select Generic roughness to specify more general roughness types.

Select Slip to set the velocity component normal to the wall to zero .

The Navier slip condition enforces no-penetration at the wall, , and adds a friction force of the form

where β is a slip length. For more information, see the Navier Slip option in the Wall feature.

The Translational velocity setting controls the translational wall velocity, utr. The list is per default set to Automatic from frame. The physics automatically detects if the spatial frame moves. This can for example happen if an ALE interface is present in the model component. If there is no movement utr = 0. If the frame moves, utr becomes equal to the frame movement. utr is accounted for in the actual boundary condition prescribed in the Boundary condition section.

Select Manual from Translational velocity selection list in order to manually prescribe Velocity of moving wall, utr. This can for example be used to model an oscillating wall where the magnitude of the oscillations are very small compared to the rest of the model. Specifying translational velocity manually does not automatically cause the associated wall to move. An additional Moving Mesh interface needs to be added to physically track the wall movement in the spatial reference frame.

This section is displayed by clicking the Show More Options button () and selecting Advanced Physics Options.