Flow Boundary Condition

Use a Flow Boundary Condition simulation object to:

• Model devices that move the fluid, such as fans or pumps.

• Model the known movement of the entire model through a stationary fluid, as when analyzing the air flow around a moving object.

• Model openings in the boundary of the fluid domain through which fluid enters or leaves at a specified pressure, such as a vent or other passive opening.

• Model bursting membranes or opening and closing of flaps on flow surfaces inside a fluid domain.

You can select different ways to model fluid flow into, out of, or within the fluid model. See Flow Boundary Condition types for more information.

Flow Boundary Condition requirements

You define a Flow Boundary Condition on one or more faces adjacent and related to the 3D fluid elements:

• The faces must lie on the boundary of the fluid domain for all types.

• The matching faces of embedded flow surfaces must have matching non-duplicate nodes. You can ensure node matching using mesh mating conditions. For more information, see Mesh mating conditions.

• The faces do not need to be meshed. However, they can be meshed with 2D elements.

• The density of the 3D flow mesh adjoining a Flow Boundary Condition is important. The solver needs at least two fluid elements across any opening for accurate modeling.

Supported variables

The following table lists the independent variables for the Flow Boundary Condition quantities that you can define using fields and expressions.

Flow Boundary Condition type	Quantity	Variables
Inlet FlowOutlet FlowInternal Fan****Recirculation Loop	Velocity****Pressure RiseNOTE	TimeSpatial variablesTime, spatial variables
Mass Flow****Volume Flow	TimeSpatial variablesTime, spatial variables
Velocity Vector	Time, spatial variables
Fan Curve	Volume flow rate
Opening****Static Pressure	Pressure	TimeSpatial variablesTime, spatial variables

In expressions, you can use all built-in functions that are listed in Mathematical functions in expressions.

Tip:

To revert back to the software behavior from previous releases, where magnitude was defined using time-varying field multiplied by a spatial distribution field, you can use the following symbolic expressions to define the Mass Flow, Volume Flow, or Fan Curve magnitude.

c*fd(“field1”)*fd(“field2”)				where:c is a constant scale factor.field1 is the name of the time-varying mass flow, volume flow, or fan curve field.field2 is the name of the dimensionless spatial distribution field. It is optional.

Where do I find it?

Application	Pre/Post
Command Finder	Flow Boundary Condition
Simulation Navigator	Right-click Simulation Object node→New Simulation Object→Flow Boundary Condition

How do I

Create a Flow Boundary Condition

Learn more

Flow Boundary Condition types

Modeling fan swirl

Working with fan curves

Modeling heat loss or gain in a recirculation loop

Flow boundary condition modeling

External Conditions

Fan Speed Controller

Inputs to expressions

Look up more details

Auto-generated expressions

Quick links

Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal boundary conditions

Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal

Command reference

Pre/Post video examples

Bulk Entry Descriptions

Simcenter 3D tutorials

Browse Simcenter 3D help by product area

Flow Boundary Condition, Simcenter 3D 2021.1 Series

© 2020 Siemens

N/A for internal fan and recirculation loop.

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