Setting Boundary Conditions

You can specify inflow and wall boundary conditions for an SPH Flow simulation.

The following options are available:
  • Wall—represents an impermeable surface that confines the fluid region. The fluid can stick to the wall (no-slip wall) or slide along it (slip wall).
  • Velocity Inlet—introduces fluid into the computational domain with a prescribed velocity.
  • Mass Flow Inlet—introduces fluid into the computational domain with a prescribed mass flow rate or the mass flux (mass flow rate per unit area).

    You are advised to avoid using geometries with complex curvature for inlet boundaries to prevent instabilities in the simulation.

To set boundary conditions:

  1. For a wall boundary, select the Regions > [surface region] > Boundaries > [boundary] node and set boundary condition Type to Wall.
    1. To specify which shear stress condition you want to impose, select [wall boundary] > Physics Conditions > Shear Stress Specification node and set Method to one of the following:
      • No-slip wall—the fluid sticks to the wall and moves with the same velocity as the wall. This option is only valid for viscous fluids.
      • Slip wall—the fluid does not stick to the wall. No wall-induced shear stress is considered for the fluid.
    2. If you want to disable the attractive forces between particles and the walls, select [wall boundary] > Physics Conditions > No-Stick Processing Option node and activate Enable No-Stick Processing Option.
  2. For an inlet boundary, select the Regions > [surface region] > Boundaries > [boundary] node and set boundary condition Type to one of the following:
    Boundary Condition Type Setting
    Velocity Inlet

    Use this option to specify an inflow velocity
    1. Select the [velocity inlet boundary] > Physics Values node and specify the Relative Velocity Magnitude values.
    Mass Flow Inlet

    Use this option to specify an inlet mass flow rate or mass flux.
    1. Select the [mass flow inlet boundary] > Physics Conditions > Mass Flow Option node and set Specification Option to one of the following:
      Specification Option Setting
      Mass Flow Rate Select the [mass flow inlet boundary] > Physics Values node and specify the Relative Mass Flow Rate. values.
      Mass Flux Select the [mass flow inlet boundary] > Physics Values node and specify the Relative Mass Flux values.
    For further information, see Boundary Settings.
In SPH flow, fluid particles consider boundary conditions only on the positive side of a boundary. Examine the normal directions to determine the accuracy of boundaries representation, and to ensure that inlets inject fluid particles in the desired boundary-normal direction. See Orienting Boundary Normals.