Create an Opening Condition

• On the ribbon, click Flow Simulation > Insert > Conditions > Boundary Condition.

• On the toolbars, click Boundary Condition on the Flow Simulation Features toolbar.

• In the menu, select Tools > Flow Simulation > Insert > Boundary Condition.

• In the Flow Simulation Analysis tree, right-click the Boundary Conditions item and select Insert Boundary Condition.

• Right-click a model face in the graphics area and select Insert Boundary Condition to create a boundary condition on the selected face.

The selected faces and components appear in the Faces to Apply the Boundary Condition  list.

In case of several fluid subdomains, the Fluid Subdomain  list is available for selecting the desired fluid region. If the CAD Boolean or Preprocessor Boolean geometry recognition is specified, this list is for information only (see “Specify an Analysis Type and Physical Features” for details).

You can also select a reference coordinate system, if you intend to specify either a fluid swirl or 3D velocity vectors, or non-uniform flow parameter distribution over the selected faces:

• The reference Coordinate System  selected by default can be:

  • Face Coordinate System (for single planar faces). The origin of face coordinate system is located at the center of the face and its X axis is oriented normally to the face.

  • Global Coordinate System (for non-planar faces or if more than one planar face is selected). See “Global Coordinate System” for details.

  Tip

  You can replace the default coordinate system by selecting your coordinate system in the flyout FeatureManager design tree.

  To create a coordinate system, click Insert > Reference Geometry > Coordinate System.

• If you want to use a cylindrical Coordinate System, select the axis of the specified Coordinate System as the Reference axis. The selected Coordinate System and Reference axis also define a local spherical coordinate system.

• Flow Openings .

  The Velocity, Mach Number (only for gases), Mass Flux (only for Inlet), Mass Flow rate or Volume Flow rate can be specified for a fluid that flows through an opening.

  By specifying an Inlet or Outlet parameter, you define the flow direction with respect to the model.

  Additionally, for Inlet conditions you can specify fluid temperature, concentrations (for multiple fluids), turbulence parameters, the relative humidity parameters (for gases), and boundary layer parameters (see below).

• Pressure Openings .

  Allows you to specify Static Pressure, Total Pressure or Environment Pressure on the selected faces. The Environment Pressure condition is interpreted by Flow Simulation as a total pressure for inlet flows and as a static pressure for outlet flows. If in the course of calculation a vortex crosses an opening with the Environment pressure condition specified, this pressure is considered as the total pressure for the part of opening through which the flow enters the model and as the static pressure for the part of opening through which the flow leaves the model. Additionally, you can specify fluid temperature (and concentrations for multiple fluids), turbulence parameters and boundary layer parameters. These settings define the fluid entering the model through the opening.

• Walls 

  Allows you to specify wall conditions on the selected faces (see“Create a Wall Condition” for details).

If you want to specify a coordinate-dependent value, Dependency  to the right of the parameter value input box (see “Dependency” for details).

• For Flow Openings, under Flow Parameters, depending on the selected boundary condition type, you can specify velocity, Mach number (only for gases), mass flow rate or volume flow rate, as well as flow velocity or direction vector for both inlet and outlet openings (see “Specify Flow Parameters” for details).

• For Inlet Flow Openings and Pressure Openings, under Thermodynamic Parameters, the pressure and temperature can be specified for Pressure Openings or inlet Flow Openings (see“Specify Thermodynamic Parameters” for details).

• If the relative humidity of gas or mixture of gases is calculated in the project (if the Humidity option is enabled on the Fluids tab in the Wizard or General Settings dialog), for Inlet Flow Openings and under Humidity Parameters you can specify the following parameters:

  • Relative Humidity  value (for inlet flow and pressure openings),

  • Humidity Reference Pressure  value (for inlet flow openings only),

  • Humidity Reference Temperature  value, under which the relative humidity has been determined (for inlet flow openings only).

  See “Relative Humidity” for details.

• For Inlet Flow Openings and Pressure Openings, under Substance Concentrations (if the number of fluids selected as default fluids on the Fluids tab of the Wizard or General Settings dialog is greater than one) the relative concentrations can be specified either by Mass fractions or Volume fractions.

  Note:

  Concentration values specified for Pressure Openings are only used if the flow calculation determines that the opening is an inlet.

  Concentrations of Immiscible Mixture  with a Free Surface are defined by fluid volume fractions (see “Free Surface” for details). You can specify the Initial fluid distribution as a constant or as a tabular dependency on the height. The height is measured from the origin of the Coordinate System specified under Selection (see “Selection List” for details).

• For Inlet Flow Openings and Pressure Openings, under Turbulence Parameters you can specify parameters of turbulence in the inlet flow in terms of:

  • Turbulence Intensity and Length . Specify the values of Turbulence Intensity  and Turbulence Length .

  • Turbulence Energy and Dissipation . Specify the values of Turbulence Energy  and Turbulence Dissipation .

  Note:

  Please note that turbulence parameters specified for Pressure Openings are used only if the flow calculation determines that the opening is an inlet.

• For Inlet Flow Openings and Pressure Openings, under Boundary Layer you can specify parameters of the boundary layer in the inlet flow:

  • You can define the Boundary Layer Type, either Turbulent (default) or Laminar.

    Note:

    If the Laminar Only flow type is selected on the Fluids tab of the Wizard or General Settings dialog, the entire flow field, including the boundary layer, is considered laminar.

  • If Inlet Velocity is selected as the boundary condition type, you can select Set parameters and specify additional boundary layer parameters: Dynamic Boundary Layer Thickness  and Heat Boundary Layer Thickness  and the external (with respect to the boundary layer) flow velocity and temperature (Core Velocity  and Core Temperature ).

  • If Inlet Mass Flow or Inlet Volume Flow is selected as the boundary condition type, the boundary layer thickness is considered equal to zero.

  Note:

  Boundary layer parameters specified for the Pressure Openings are used only if the flow calculation determines that the opening is an inlet.

It is often convenient to specify an appropriate goal along with the boundary condition. For example, if you specify a pressure opening, it makes sense to define a mass flow rate surface goal for this opening.

The default template is <Type> and <Number>, where <Type> is the boundary condition type and <Number> is the sequential number of the boundary condition in the Flow Simulation Analysis tree. When boundary condition is created, <Type> is replaced by the boundary condition type (for instance, “Inlet Mass Flow”) and <Number> is replaced by the sequential number of the boundary condition (for example, if the boundary condition named “Inlet Mass Flow 1” already exists, the new boundary condition will be named “Inlet Mass Flow 2” and so on). You can combine these standard elements in any order and add any appropriate characters to the template. To add a new standard element to the template, click the Type  or Number  button.

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Click Keep Visible  before clicking OK  to keep the dialog open and define more boundary conditions.