Stopping the Flow

You can use the melting-solidification flow stop functionality when you want to prevent all flow (not allowing slow creeping flow) or when the solid needs to withstand high pressure gradients.

Flow stopped cells have zero velocity (relative to the cell center velocity) and a pressure equal to the face-weighted average pressure of all adjacent non-stopped cells. However, if a flow stopped cell is only next to other flow stopped cells, the static pressure is equal to the reference pressure, as this model does not calculate stresses in the solid.

When you use the flow stop functionality, the following limitations apply:

  • The flow stop solid fraction does not apply to regions that are subject to motion that affects the mesh volume (for example, Morpher or User-Defined Vertex Motion).

    In morphed regions, the flow stop flag is set to zero for every cell (that is, there are no flow-stopped cells at any time).

  • The face between a stopped and a non-stopped cell is not a wall.

    No wall boundary conditions for flow (such as slip/no-slip, or wall function) or turbulence are applied to faces between stopped cells and non-stopped cells.

To stop the flow:

  1. In the physics continuum, open the Physics Model Selection dialog and select Melting-Solidification Flow Stop from the Optional Models group box.

    This model stops the fluid flow in a cell at a specified solid volume fraction.

  2. For each relevant phase, select the Material Properties > Flowability Threshold node and specify the limit for the relative solid volume fraction at which the particular phase loses its ability to flow.

    The value that you specify depends on the properties of the material. Valid values are from 0 through 1.

  3. Select the Regions > [Region] > Physics Values > Flow Stop Solid Fraction node and specify the limit for the accumulated volume fraction of non-flowable phases (that is, those phases where the Flow Stop Flag = 1) at which the fluid flow is stopped in a cell.

    This setting is a property of the continuum, so it depends on all of the phases that are present. The fluid velocity is set to zero for cells that have a solid volume fraction above the specified flow stop value. Valid values are from 0 through 1.

  4. If you want to deactivate the Melting-Solidification Flow Stop model for a particular region, select the Regions > [Region] > Physics Conditions > Flow Stop Option node and deselect Flow Stop Option.

If your simulation uses a compressible equation of state (Polynomial Density or User Defined EOS), activate the Flow Stop Mass Compensation model.

  1. In the physics continuum, open the Physics Model Selection dialog and select Flow Stop Mass Compensation from the Optional Models group box.

    When this option is activated, the density of all VOF phases in stopped cells is kept constant at the value that it had at the time when the cell was stopped. This value is maintained independently of what the equation of state returns for the VOF phase. The constant density is required to keep the mass in the stopped cells constant when cell volume is kept constant and the dependency of density on stresses is omitted. The density in not-stopped cells is not modified. Also, the separate material properties Density Temperature Derivative and Density Pressure Derivative are not adjusted accordingly.