Baffle Interface

A baffle interface physically represents one or more thin sheets of solid materials in a fluid. By default, baffles are impermeable to fluids, but they can be made selectively permeable to components of gas mixtures. You can also take into account heat conduction through a baffle by specifying a thermal resistance.

A baffle can be placed between regions of the same continuum or of different continua. The thickness of a baffle is infinitesimal. The fluid next to a baffle treats the baffle as a wall. It applies the non-slip boundary condition in viscous flow, and the component of the velocity normal to the baffle is zero.

Membrane Modeling

For flows of multicomponent gas mixtures, the baffle interface can be used to model a membrane that is selectively permeable to individual components of the gas mixture.

The mass flux

m_{i}

of gas mixture component

i

from side 0 to side 1 of the baffle is computed as:

图 1. EQUATION_DISPLAY

{\dot{m}}_{i} = L_{i} \cdot Δ f_{i}

(80)

where:

$L_{i}$ is the permeance of gas mixture component $i$ in kg/(m² s Pa).
$Δ f_{i} = {f_{i} |}_{0} - {f_{i} |}_{1}$ is the fugacity difference of gas mixture component $i$ across the membrane in Pa.

Fugacity is the partial pressure of the gas mixture component $i$ , and given by:

图 2. EQUATION_DISPLAY

f_{i} = ϕ_{i} \cdot X_{i} \cdot P

(81)

where:

$ϕ_{i}$ is the fugacity coefficient.
$X_{i}$ is the mole fraction.
$P$ is the absolute pressure.

For ideal gases, the fugacity coefficient equals 1. For real gases, the fugacity coefficient depends on the composition of the gas mixture.

Thermal Modeling

A thermal resistance per unit area $R$ for conjugate heat transfer can be specified, either as effective resistance or with multiple layers. The relation between the heat flux across the contact interface, $\ddot{\dot{q}}$ , and the temperature difference, $Δ T$ , is given by Eqn. (79). To calculate the thermal resistance of the baffle, the following formula can be used:
图 3. EQUATION_DISPLAY

$\frac{1}{R} = \sum_{j}^{n} \frac{k_{j}}{Δ x_{j}}$

(82)

where $k_{j}$ and $Δ x_{j}$ are the conductivity and thickness, respectively, of each of the $n$ layers comprising the baffle.
If it is not required that heat transfer through the baffle is modeled, do not create a baffle interface. The same functionality could be achieved by assigning wall boundary types (with adiabatic thermal conditions) to the boundaries in question.

Baffle Properties

You can use the properties that are listed below to adjust the specifications of a Baffle interface node.

Geometry

Specifies the geometry source option:

Boundaries: The interface is a boundary-mode interface, which is created by selecting two boundaries.
Contacts: The interface is a contact-mode interface. which is defined directly from part contacts.

Boundary-0

Indicates the "fixed" side of the interface (Read Only).

Boundary-1

Indicates the "adapted" side of the interface (Read Only).

Vertices from boundary-1 are projected onto boundary-0. The orientation can be swapped through the right-click action Reverse Orientation.

Contacts

Displays the part surface contacts. When the Geometry property is Contacts, it shows the part surface contacts. Geometry property is Boundaries, it shows no value.

Type

Defines the type of interface. Must be set to Baffle Interface.

Topology

Defines the connection type between the interfaces:

In-place—uses the in-place topology.
Periodic—uses the periodic topology.
Repeating—uses the repeating topology.

Connectivity

Defines how the boundaries on the two sides of the interface are connected. Baffle interfaces have Imprinted connectivity type. The imprint connectivity type indicates the interface is within regions that are discretized using the finite volume method. The imprint procedure creates intersected faces.

Allow Per-Contact Values

Allows you to define the interface tolerance individually for each contact. Activates the child property Specify by Part Subgroup.

注	This property is only valid for contact-mode boundary interfaces. See also: Contact-Mode Boundary Interfaces.

Close Adjacent Cells

Creates a watertight intersection by fixing the cell connectivity between the interface faces and side faces along common edges.

With this option, the topology-based intersector adds extra edges to eliminate the gap between the sides, which reduces spurious oscillations in physical quantities.

This property is only available when the Direct Intersector of the Interface Manager node is set to Topology-Based and the Connectivity of the interface is Imprinted.

注	Close Adjacent Cells is not compatible with DFBI Motion.

Reset on Relative Motion

When activated, the interface is reset when there is any relative motion between the two sides.
When deactivated, the interface is reset when the relative motion between the two sides exceeds a relative tolerance based upon minimum edge length.

注	This property is only available when the Connectivity of the interface is Imprinted.

Baffle Conditions

You can use the properties that are listed below to adjust the specifications of a Physics Condition interface node.

Baffle Species Option

Specifies whether the baffle is impermeable or selectively permeable to certain components of a multi-component gas mixture. Available only if Multi-Component Gas is selected in the physics continuum and the same physics continuum is used on both sides of the baffle.

Impermeable: The baffle is impermeable to fluids. This is the default.
Permeable: The baffle is permeable to components of a gas mixture. This option adds the Species Permeance node to Physics Values on this baffle interface. Removes the Wall Species Option node from both corresponding baffle boundaries in the region.

Baffle Thermal Option

Specifies whether the baffle conducts energy.

Conducting: Thermal conduction occurs through the baffle. You would typically select this option when you use an energy model and a baffle or porous baffle interface. A Thermal Resistance interface value is added.
Non-conducting: No thermal conduction occurs through the baffle.

Energy Source Option

Provides energy source options for the interface. It is activated when the Baffle Thermal Option is set to Conducting.

None: Do not specify an energy source.
Heat Flux: Specifies a user-defined heat flux in W/m².
Heat Source: Specifies a user-defined heat source in W.

Baffle Values

You can use the properties that are listed below to adjust the specifications of a Physics Values interface node.

Intersection

Available for all direct interfaces to control the intersection tolerance. The available properties for baffle interfaces are:

Specify by Part Subgroup: Specifies sub-grouping for contact-mode boundary interfaces to set up independent intersection properties. See also Contact-Mode Boundary Interfaces and 调整交界面相交容差（基于几何的方法）.

The remaining properties depend on the setting for the Direct Intersector property. This property is set on the Interfaces node (see Interfaces Properties):

Geometry-Based (Legacy)

This Direct Intersector option activates:

Geometric Tolerance: Specifies the maximum projection distance of adapted vertices onto the fixed side in terms of a fraction of minimum local edge length around each vertex. For more details, refer to 调整交界面相交容差（基于几何的方法）.

Topology-Based with Connectivity Imprinted

Match Outer Boundary: when activated, indicates that the interface boundaries are expected to fully overlap on large-scale topological features. Activate this option only when you expect a complete match of the two boundaries of an interface.
By default, this property is deactivated.
Projection Tolerance: maximum orthogonal projection distance in terms of a fraction of local element diameter. Places a limit on how the vertices of the adapted side get projected onto the fixed side. In cases where the two interface boundaries are separated by greater distances, you can increase the Projection Tolerance value to get fewer remainder faces.
By default, the tolerance is set to 0.2.
Angle Threshold: maximum angle (deg) by which the intersector identifies large-scale features that are mapped from the adapted side onto the fixed side. To preserve sharper features, specify a smaller Angle Threshold value. If the boundary meshes have spurious defects, you can specify a larger value.
By default, the value is set to 45 deg.

Thermal Resistance

The value of the resistance to conduction through the baffle. It is activated when the Baffle Thermal Option is set to Conducting.

A Thermal Resistance boundary value is added to the object tree when the Thermal Specification boundary condition is set to Environment. Properties:

Dimensions—Specify the resistance in units of $m^{2} \cdot K / W$ or similar. (Read Only)
Method—Specify the input method type from Constant, Field Function, Table, User Code, or Multi-Layer Resistance.

Heat Flux

Specify the heat transferred per unit area. It is activated when the Energy Source Option is set to Heat Flux. Properties:

Dimensions—Specify the heat flux in units of $W / m^{2}$ or similar. (Read Only)
Method—Specify the input method type from Constant, Field Function, Table, or User Code.

Heat Source

Specify the heat transferred. It is activated when the Energy Source Option is set to Heat Source. Properties:

Dimensions—Specify the heat source in units of $W$ or similar. (Read Only)
Method—Specify the input method type from Constant, Field Function, Table, or User Code.

Species Permeance

Specifies the permeance of gas mixture component

i

diffusing through a permeable baffle.

L_{i}

in Eqn. (80). Available if Baffle Species Option under the Physics > Conditions > Baffle Species Option node is set to Permeable.

Method	Corresponding Physics Value Nodes
Constant Uses a single value for all gas mixture components. Can be used for non-component-selective membranes.	None
Composite Can be used for component-selective membranes. Each component can use a different specification method. Non-constant field functions can be used to model spatial membrane thickness changes that are all combined in the permeance value. A permeance of 0 is the same as an impermeable membrane for the respective component.	Composite > [component 1], [component 2], ...

Baffle Values: Multi-Layer Resistance

This Thermal Resistance value is useful when, for example, you are simulating conduction through multiple materials that vary in conductivity. It is calculated using Eqn. (82).

This object is also available in the Thermal Resistance boundary value, which is added to the object tree when the Thermal Specification boundary condition is set to Environment.

Multi-Layer Resistance Properties

Number of layers

Specifies the number of layers within the baffle.

Thickness of each layer

Sets a thickness for each of the layers. The number of comma-separated entries must match the number of layers. If the number of layers is decreased, the last value is dropped. If a layer is added, a zero value is appended by default.

Conductivity of each layer

Specifies the conductivity through a series of comma-separated values equal to the number of layers.

Simcenter STAR-CCM+ works with discrepancies between these specifications as follows:

If you make more conductivity value entries than layers, for example seven values and five layers, then Simcenter STAR-CCM+ works with the first five values.
If you make fewer conductivity value entries than layers, for example three values and five layers, Simcenter STAR-CCM+ interprets values for the remaining layers as zero conductivity.