Setting Up the Relative Velocity Field for the Mushy Zone Permeability Model

Generally, the Mushy Zone Permeability model applies a momentum source term to stop the flow of the solidified liquid. The flow is stopped by reducing the convective velocity to zero with respect to the laboratory coordinate system.

For some applications, it can be useful to specify a non-zero velocity field for the solidified liquid. For example:

  • Centrifugal casting

    Liquid melt is injected through a nozzle splashing onto the inner wall of a rotating cylinder. When solidification takes place, the solidified liquid must rotate at the same angular velocity as the rotating cylinder so the solidified liquid has zero velocity relative to the rotating wall.

  • Continuous/Strand casting

    Liquid melt is injected at the top of an open-base mold. In the mold, a thin sheet of metal next to the mold wall solidifies. The solidified liquid has to move at the same velocity as the strand is pulled away. The velocity with which the mold wall and the solidified liquid move (with zero relative velocity between them) is called the pull velocity.

To set up a relative velocity field for the Mushy Zone Permeability model:

  1. Set up the appropriate stationary moving reference frame motion or rigid body motion model.

    You can specify any motion except motions that affect the cell volume (such as the morpher).

    See Working with Motions.

  2. In the appropriate region, select the Physics Conditions > Mushy Zone Reference Frame Specification node.


  3. In the Mushy Zone Reference Frame Specification - Properties window, select the appropriate reference frame option:
    • Region Reference Frame

      The relative velocity is specified with respect to the region reference frame. The region reference frame is the motion reference frame, which is selected in Physics Values > Motion Specification > Reference Frame.

    • Lab Frame

      The relative velocity is specified with respect to the laboratory reference frame.

    • Local Reference Frame

      The relative velocity is specified with respect to a local reference frame with which the region is associated.

    The corresponding nodes are added to the Physics Values node of the region.

  4. Specify the relative velocity field with respect to your selected reference frame:
    • For a region reference frame:

      Select the Physics Values > Mushy Zone Relative Velocity node and set its scalar profile method and value.



    • For the laboratory reference frame:

      Select the Physics Values > Mushy Zone Velocity node and set its scalar profile method and value.



    • For the local reference frame:
      1. Select the Physics Values > Mushy Zone Local Reference Frame Specification node.
      2. In the Properties window, select the local reference frame that resides in Tools > Reference Frames to describe the motion.
      3. Select the Physics Values > Mushy Zone Relative Velocity node and set its scalar profile method and value.


When you specify the relative velocity value, observe the following difference between a stationary moving reference motion and a rigid body motion:

  • For a rigid body motion, the mesh actually moves in the Reference Frame for Rotation. Therefore, you specify a relative velocity value of zero with respect to the Coordinate System in the Mushy Zone Relative Velocity - Properties window. The solidified liquid moves with the velocity specified for the rigid body motion.
  • For a moving reference frame motion, the simulation is stationary and the mesh does not actually move. Therefore, you specify a non-zero relative velocity value with respect to the Coordinate System in the Mushy Zone Relative Velocity - Properties window. The solidified liquid moves with the velocity specified for the moving reference frame motion.