Pre Boundary Conditions

CFX-Pre Master Master Help On
Contents Index Help
CFX-Pre

Boundary Conditions

• Introduction to Boundary Conditions p. 260

• Default Boundary Conditions p. 263

• Interface Boundary Conditions p. 264

• Basic Settings p. 265

• Boundary Details p. 271

• Fluid Values p. 289

• Mesh Motion p. 297

• Plot Options p. 298

Page 259 CFX-5.7.1

CFX-PreBoundary Conditions

Master Master Help On
Contents Index Help
Introduction to Boundary Conditions

Boundary Conditions must be applied to all regions at the outer extremities of your domain(s). Boundary Conditions can be inlets, outlets, openings, walls and symmetry planes (periodic interfaces are specified on the Domain Interfaces form: see Periodic Interfaces (p. 304)). Unspecified external regions are automatically assigned a no-slip, adiabatic wall boundary condition. Such regions assume the name <Domain> Default, where <Domain> corresponds to the name of the domain. Unspecified internal boundaries are ignored.

Boundary conditions can be applied to any bounding surface of a 3D primitive that is included in a domain (i.e. including internal surfaces). If you choose to specify a boundary condition on an internal surface (e.g. to create a thin surface), then a boundary condition must be applied to both sides of the surface.

Boundary Condition ActionsRight-clicking on a boundary condition in the Object Selector tree (Physics Selector (p. 12)) gives a list of options, which are described below.

The New feature is not employed for Boundary Conditions.

Edit the boundary condition using the GUI forms

Use the copy and paste features to replicate boundaries. Boundaries should be pasted onto Domain objects.

Open the Command Editor to view/edit the CCL definition of objects.

If physics errors exist (the boundary is coloured red), you can attempt to automatically correct the physics. See Physics Checking (p. 16).

This option is available when you have created a plot on a boundary condition, and is enabled when right-clicking on the Boundary Contour object within a boundary. See Plot Options (p. 298).

Delete a boundary.

Page 260 Introduction to Boundary Conditions CFX-5.7.1


Contents Index Help
Displaying Boundary ConditionsWhen you create a boundary condition in CFX-Pre, the regions comprising the boundary condition are highlighted according to the highlight settings you have specified on the Edit > Options form (see Highlighting (p. 76)). Symbols for certain boundary conditions are also displayed in the viewer. The boundary condition symbols are shown at surface display line intersections.

Inlets use arrows pointing into the Fluid Domain (denoting inflow), while Outlets use arrows pointing out of the Fluid Domain (denoting outflow).

The boundary condition symbols and default colour schemes are:

• Inlet - White arrows

• Outlet - Yellow arrows

• Opening - Blue bi-directional arrows

• Symmetry - Red arrows on each side of the surface

• Interface:

• Fluid-Fluid, Fluid-Solid and Solid-Solid - Green octahedra• Periodic - Purple semi-circular arrows

Considerations For VisualisationWhen you create boundary conditions, the boundary names appear under the Domain object in CFX-Post. Plots can still be created, however, on any primitive region, as all regions are written to the definition and results files.

Creating or Editing a Boundary ConditionTo create or edit a boundary condition, select Create > Flow Objects > Boundary Conditions from the main menu bar, or click the Boundary Conditions icon. You can also edit existing boundaries by right-clicking on their name in the Object Selector. See Physics Selector (p. 12).

Important: Inlets, Outlets and Openings use arrow symbols whose direction is locally normal to the boundary surface, irrespective of the actual direction specified for the boundary condition. It is possible to show arrows pointing in the specified direction by creating a Boundary Vector object (see Boundary Vector p. 298 for details) and then turning off the default arrow symbols (see Boundary Marker Options (p. 78) for details).

Boundary Conditions icon



Contents Index Help
When you create or edit a new boundary condition, a panel will appear requesting the a name for the boundary. Use the drop-down list to find the boundary to edit, or enter a new name. Select a domain to which the boundary will apply. Valid Syntax for Named Objects (p. 15) give more details on valid names.

Boundary Conditions can only apply to one domain. A domain must be created before any boundary conditions can be applied.



Contents Index Help
Default Boundary Conditions

You should be familiar with the concept of primitive and composite regions before reading this section: see Mesh Topology in CFX-Pre (p. 81).

All “fluid-world” 2D primitives are assigned to the “Domain Name Default” boundary condition when its parent 3D primitive is included in a domain. Each new domain has its own “Domain Name Default” boundary. When 2D primitives (or composites that reference them) are assigned to other boundary conditions and domain interfaces, they are removed from the “Domain Name Default” boundary condition. A “fluid-world” 2D primitive is one that forms the boundary between the fluid(s) in the simulation and the outside world that is not modelled. The “Domain Name Default” boundary condition is a no-slip adiabatic wall, but this can be edited like any other boundary condition. Solid-world 2D primitives behave in a similar way.

“Fluid-solid” regions are also initially contained in the “Domain Name Default” boundary condition. When a Solver (Definition) file is written, any fluid-solid regions in the “Domain Name Default” boundary condition are removed and assigned to automatically generated Fluid-Solid Domain Interfaces.

If every region is assigned to another boundary condition, the “Domain Name Default” boundary object will cease to exist. In such a case, if a boundary condition is subsequently deleted, the “Domain Name Default” wall boundary will be re-created for the unspecified region. Since the “Domain Name Default” wall boundary condition is controlled automatically, you should never need to explicitly edit its Location list.

Fluid-fluid 2D primitives (i.e. internal 2D primitives) are ignored unless a boundary condition is explicitly assigned (these are then thin surfaces). Each side of a fluid-fluid 2D primitive can have a different boundary condition, but most often both sides will be a wall. Thin surfaces are created by assigning a wall boundary condition to each side of a fluid-fluid 2D region. You can specify thin surfaces in CFX-Pre by specifying one side of each thin surface and selecting the Create Thin Surface Partner (p. 267) toggle on the Basic Settings panel for wall boundary conditions.

Solid-solid 2D primitives are always ignored since you cannot create a boundary condition inside a solid domain.

Page 263 Default Boundary Conditions CFX-5.7.1


Contents Index Help
Interface Boundary Conditions

All Domain Interfaces automatically create boundaries of type “Interface” that contain the regions used in the Domain Interface. These boundaries are named “< Domain Interface Name > Side <Domain Name> Part < 1/2 >”, At least one of these boundaries will be auto-created for each domain involved in the interface. You can edit these boundaries like any other boundary, but you cannot create new Interface boundaries directly.

You will usually not need to edit an auto-generated Interface boundary, but options are available for Fluid-Solid interfaces (which can be considered as being a special case of wall boundaries). The settings and options available when editing Interface Boundaries are described in Boundary Details: Interface (p. 286) and Fluid Values: Interface (p. 294).

Page 264 Interface Boundary Conditions CFX-5.7.1


Contents Index Help
Basic Settings

The basic settings for boundary condition are to set the type, location, coordinate frame, and frame type (stationary or rotating) for each.

Boundary Type

Inlet, Outlet, Opening, Wall and Symmetry boundary conditions can be created. Interface boundaries can be edited, but not created.

Location

The Location list contains all 2D Composite and Primitive regions. For a discussion of primitive and composite regions, please refer to Mesh Topology in CFX-Pre (p. 81). Multiple 2D regions can be selected by holding the <Ctrl> key as you select additional regions.

Select the Location(s); the drop-down list contains the commonly used regions (all the composite names and the primitive names that are not referenced by any composites). Hold the <Ctrl> key to select multiple regions. The extended list contains all regions in a domain. Alternatively, use the picking tool to select locations from the viewer using the mouse. See Boundary Condition and Domain Interface Locations (p. 82 in CFX-Pre).

Choose a Coordinate Frame. See Coord Frame (p. 266).

For Rotating Domains, select the frame type. See Frame Type (p. 266).

For creating a boundary condition that forms a pair with this one. See Create Thin Surface Partner (p. 267)

Use profile data to define this boundary condition. See Profile Boundary Conditions (p. 78 in CFX-5 Solver Modelling)

Select the Boundary Type.

Page 265 Basic Settings CFX-5.7.1


Contents Index Help
Coord Frame

Coordinate frames are used to determine the principal reference directions of specified and solved vector quantities in your Domain, and for specifying reference directions when creating boundary conditions or setting initial values. By default, CFX-Pre uses Coord 0 as the Reference Coordinate Frame for all specifications in the model, but this can be changed to any valid CFX-Pre coordinate frame. See Global Coordinate Frame (Coord 0) (p. 23 in CFX-5 Solver Modelling) for more details.

Frame Type

CFX-Pre treats boundary conditions differently when a Rotating Frame of Reference has been specified for the domain. Under these circumstances, the option to set Frame to Rotating or Stationary appears on the Boundary Conditions panel.

The term rotating frame is the Rotating Frame of Reference itself. Selecting the Rotating option means that all values are set relative to the rotating frame. An Inlet boundary condition prescribed using the Rotating option rotates about the same axis as the Domain.

The term stationary frame is a frame of reference that is stationary and does not rotate with the Rotating Frame of Reference. For example, an Inlet boundary condition specified with the Stationary option does not rotate about the axis along with the domain.

A discussion of the Frame Type on cartesian and cylindrical velocity components is given in Cartesian Velocity Components (p. 55 in CFX-5 Solver Modelling) and Cylindrical Velocity Components (p. 55 in CFX-5 Solver Modelling).



Contents Index Help
Create Thin Surface Partner

Wall Boundary conditions have an additional toggle which, when selected, will attempt to create an identical boundary condition on the other side of the specified region. This is useful for modeling very thin surfaces, such as baffles. After creation, these boundaries can be edited in order to apply slightly different physical boundary conditions to either side of the region.

If creating a thin surface boundary condition, enable the toggle. Select one side of each thin surface boundary in the Location list.



Contents Index Help
Use Profile Data

In order to specify a boundary condition using a data file that describes a profile distribution, you must first read in your profile data file. Select Tools > Initialise Profile Data to select the file to read.

Initialise Profile Data

Profile boundary conditions refer to the boundary conditions whose data vary spatially over the boundary condition region. The variation of the data is specified in a number of ways including form functions, user Fortran, and in term of discrete data values (and locations).

Types of Discrete Profiles• 1-D profile uses one spatial coordinate to define the data position, for e.g., x, y, z or a

cylindrical value. This could be used to describe the axisymmetric flow down a cylindrical pipe (i.e. the data values for a value of ‘r’).

• 2-D profile uses two spatial coordinates (cartesian or polar), for e.g., (x, y), (x, z), (r, t), (a, t), etc. if you are importing the data from a 2D code on a planar boundary, you may wish to use this as a boundary condition in a 3D case in CFX.

• 3-D profile uses three spatial coordinates, for e.g., (x, y, z) or (r, t, a). Among various uses of 3-D Profile Data are boundary conditions, spatially varying fluid properties, additional variables or equation sources.

Profile Data FormatThe format of the profile data file is shown below:# Comment line# The following section (beginning with [Name] and ending as [Elements]) # represents one profile, which can be repeated to define multiple profiles.

Click to Browse to the file containing your profile data.

The fields are displayed in the output.



Contents Index Help
[Name]My Boundary

[Spatial Fields]r [m], theta [degrees], z [m]...[Data]X [ m ], Y [ m ], Z [ m ], Area [ m^2 ], Density [ kg m^-3 ]-1.77312009e-02, -5.38203605e-02, 6.00000024e-02, 7.12153496e-06, 1.23141646e+00-1.77312009e-02, -5.79627529e-02, 5.99999949e-02, 5.06326614e-06, 1.23143399e+00...# -------- end of first profile 'My Boundary'----------

[Name]Plane 2...

The guidelines for creating profile data format are listed below:

• The name of each Locator is listed under the ‘[Name]’ heading.

• The names of the fields are case insensitive (i.e. [data] and [Data] are acceptable).

• The names of variables used in the data fields are case sensitive.

For e.g., 'u [m]' is valid x velocity component, whereas 'U [m]' is unrecognized field name. You have to map this unrecognized field name with valid variable name when loading in to CFX-Pre. This is consistent with the use of CEL elsewhere.

• Comments in the file are preceded by # (or ## for the CFX-5.6 polyline format) and can appear anywhere in the file.

• Commas must separate all fields in the profile. Any trailing commas at the end of a line is ignored. Any additional commas within a line of data will be a syntax error.

• Blank lines are ignored and can appear anywhere in the file (except between the [<data>] and first data line, where <data> is one of the key words in square brackets shown in the data format).

• If any lines with text are included above the keyword '[Name]', a syntax error will occur. Such lines should be preceded by # character to convert them into comments.

• Multiple data sets are permitted within the same file by repeating the sequence of profiles; each profile begins with keyword '[Name]'.

• Point coordinates and the corresponding variable values are stored in the Data section.

• The ‘[Spatial Fields]’ can contain 1, 2, or 3 values, corresponding to whether this data is 1D, 2D or 3D.



Contents Index Help
• The data file has a .csv extension for compatibility with other software packages.

• When this data file is read-in, it is checked for any format violations; physics error is shown for such situations. See Physics Checking (p. 16 in CFX-Pre) and The RULES and VARIABLES Files (p. 79 in CFX-Solver Manager).

Example: Consider a multiphase boundary condition is set up using the profile data file having a profile named myProfile and one of data fields is Temperature [K]. CFX-Pre allows function as myProfile.water.Temperature(x,y,z) in order to refer to a data field stored in the profile. This derived value can be assigned to a parameter, say Fixed Temperature.

The expressions that are automatically generated in CFX-Pre for profile boundaries are simply the expressions in terms of interpolation functions. This means that you can modify them in the same way as a normal CEL expression. For example, the expression ‘myProfile.Temperature(x,y,z)’ could be modified to ‘2*myProfile.Temperature(2x,y,z)’.

Also see Profile Boundary Conditions (p. 78 in CFX-5 Solver Modelling) for following details:

• Using a profile from one location at another location

• Standard Variable Names

• Non-standard Variable Names

• Custom variables

• Using r-theta profiles

• Data Interpolation method

• Extracting Profile Data from Results Files



Contents Index Help
Boundary Details

The values which you need to set at boundaries depend on the characteristics of the flow. For instance, you can only specify temperature at a boundary if heat transfer is being modelled.

If you change the characteristics of the flow, you must ensure that your boundary conditions are correctly specified. In most cases, CFX-Pre will alert you of the need to update settings in the form of Physics Validation errors. See Physics Checking (p. 16) for more details.

For example, suppose you create a Domain, specify isothermal flow and set an Inlet boundary condition. If you then alter the flow characteristics on the Domain form to include heat transfer, you must change the Inlet specification to include the temperature of the fluid at that location.

When modelling buoyancy, a pressure specified by a boundary condition will be interpreted as excluding any hydrostatic contribution. See Buoyancy and Pressure (p. 13 in CFX-5 Solver Modelling) and Buoyancy (p. 25 in CFX-5 Solver Theory) for details.

The following links will direct you to different Boundary Details panel descriptions:

Boundary Details: Inlet (p. 271)

Boundary Details: Outlet (p. 277)

Boundary Details: Opening (p. 280)

Boundary Details: Wall (p. 282)

Boundary Details: Interface (p. 286)

Boundary Details: InletThe following panel shows the boundary details for a single-phase, single-component simulation. For details on other types of inlet, please see:

• Boundary Details: Inlet: Rotating Frame Settings (p. 273)

• Boundary Details: Inlet: Supersonic (p. 274)

• Boundary Details: Inlet: Variable Composition or Reacting Mixture Settings (p. 275)

• Boundary Details: Inlet: Multiphase Settings (p. 275)

• Boundary Details: Inlet: Additional Variable Settings (p. 276)

Page 271 Boundary Details CFX-5.7.1


Contents Index Help
Boundary Details: Single-phase, Single Component

Choose a subsonic or supersonic inlet. For multiphase simulations, subsonic must be chosen.

Specify Mass and Momentum as:

• Normal Speed• Cartesian Velocity Components• Cylindrical Velocity Components• Mass Flow Rate• Static Pressure• Total PressureSee Mass and Momentum (p. 55 in CFX-5 Solver Modelling).

Options are different for Rotating Frames, Multiphase and Supersonic Inlets (see following pages).

Specify a Turbulence option. See Turbulence (p. 57 in CFX-5 Solver Modelling) for details on each option.

If you are modelling radiation, set one of:

• Adiabatic• Local Temperature• Radiation Intensity: the direction components of

X,Y and Z must be specified.• External Blackbody Temperature: specify a

temperature.• Radiative Heat Flux: set an inlet flux in [W m^-2].

The available options depend on the radiation model.

See Thermal Radiation (p. 60 in CFX-5 Solver

☞ More Help:• Inlet (p. 55 in CFX-5 Solver Modelling)• Inlet (subsonic) (p. 36 in CFX-5 Solver

Theory)• Recommended Configurations of Boundary

Conditions (p. 50 in CFX-5 Solver Modelling)

Specify a temperature at an Inlet boundary using:

• Static Temperature• Total Temperature (when Total

Energy Heat Transfer is used)See Heat Transfer (p. 59 in CFX-5 Solver Modelling) for details and the following pages for further model dependent options.

If an expression describes the boundary condition, use the expression editor Expressions (p. 160) to create the expression, then click the expression icon and enter the expression name.



Contents Index Help
Boundary Details: Inlet: Rotating Frame Settings

☞ More Help:• Inlet (p. 55 in CFX-5 Solver Modelling)• Inlet (subsonic) (p. 36 in CFX-5 Solver

Theory)• Recommended Configurations of Boundary

Conditions (p. 50 in CFX-5 Solver Modelling)

Specify a Turbulence option. See Turbulence (p. 57 in CFX-5 Solver Modelling) for details on each option.If you are using a radiation model, set one of:

• Adiabatic• Local Temperature• Radiation Intensity: the direction components of

X,Y and Z must be specified.• External Blackbody Temperature: specify a

temperature.• Radiative Heat Flux: set an inlet flux in [W m^-2].


See Thermal Radiation (p. 60 in CFX-5 Solver Modelling).

Flow Direction options include:

• Normal to Boundary• Cartesian Components• Cylindrical Components.See Mass and Momentum (p. 55 in CFX-5 Solver Modelling).

Specify the Flow Regime for the Inlet boundary as either Subsonic or Supersonic. See Boundary Details: Inlet: Supersonic (p. 274) for supersonic options..

Mass and Momentum as:

• Normal Speed• Cartesian Velocity Components• Cylindrical Velocity Components• Static Pressure• Stat. Frame Total Pressure• Mass Flow RateSee Mass and Momentum (p. 55 in CFX-5 Solver Modelling) for more details. Options are different for Multiphase and Supersonic Inlets (see previous and following pages).


• Static Temperature• Stationary Frame Total Temperature See Heat Transfer (p. 59 in CFX-5 Solver Modelling) for details and the following pages for further model dependent options.



Contents Index Help
Boundary Details: Inlet: Supersonic

Mass and Momentum as:

• Cartesian Velocity Components and Pressure

• Cylindrical Velocity Components and Pressure

See Mass and Momentum (p. 61 in CFX-5 Solver Modelling) for more details.

Specify a Turbulence option. See Turbulence (p. 57 in CFX-5 Solver Modelling) for details on each option.


• Static Temperature• Total Temperature (when Total Energy Heat

Transfer is used)See Heat Transfer (p. 59 in CFX-5 Solver Modelling) for details and the following pages for further model dependent options.



Contents Index Help
Boundary Details: Inlet: Variable Composition or Reacting Mixture Settings

Boundary Details: Inlet: Multiphase Settings

For a multiphase simulation using the inhomogeneous model, the fluid-independent information for an Inlet is entered on the Boundary Details panel shown below. The purpose of this panel is to specify Flow Regime and Flow Specification. When the Homogeneous model is used, the Mass and Momentum, Heat Transfer and Turbulence information is also set on this panel. These options are set on the Fluid Values panel when the inhomogeneous model is used. For both inhomogeneous and homogeneous models, a Bulk Mass Flow Rate can be specified. The Flow Direction must also be set on the Boundary Details form for this case.

The Component Details section of the panel appears when a variable composition/reacting mixture has been created for a single phase simulation, or a simulation with one continuous phase and particle tracking.

Highlight the material from the list and enter the mass fraction. Mass Fractions must sum to unity on all boundaries. To enter an expression for the mass fraction, click the Enter Expression icon and enter the name of your expression.

See Combustion Modelling (p. 257 in CFX-5 Solver Modelling) for details on each of the combustion models.

If you are using the Soot Model with Combustion, set a value for either Mass Concentration and Nuclei Concentration or Mass Fraction and Nuclei Specific Concentration.

See Soot Model (p. 281 in CFX-5 Solver Modelling).

When modelling the partially premixed combustion model, the Reaction Progress variable is also set. See Reaction Progress (p. 277 in CFX-5 Solver



Contents Index Help
The Component Details section of the panel will appear if the homogeneous model is used, and at least one of the fluids is a variable composition mixture. If the inhomogeneous model is used, component details are set for each fluid on the Fluid Values tab panel (Fluid Values: Inlet/Opening (p. 289)).

Boundary Details: Inlet: Additional Variable Settings

Subsonic flow regime must be chosen for multiphase simulations.

Options available for Mass and Momentum are:

• Cartesian Velocity Components• Cylindrical Velocity Components• Static Pressure • Total Pressure• Fluid Velocity• Bulk Mass Flow RateIf a pressure specification is chosen, enter the pressure. The direction is chosen on the Fluid Values tab panel.

If Fluid Velocity is chosen, the velocity details are entered on the Fluid Values tab panel. See Mass and Momentum (p. 55 in CFX-5 Solver Modelling).

Highlight the Additional Variable to edit, and enter its mass concentration.

For details on Additional Variables, see Additional Variables (p. 19 in CFX-5 Solver Modelling).



Contents Index Help
Boundary Details: OutletThe panel below is used to set the boundary conditions at an Outlet for a single phase stationary domain simulation.

For details on other outlet types, see Boundary Details: Outlet: Multiphase Settings (p. 278 in CFX-Pre) and Boundary Details: Outlet: Mass Flow Settings (p. 279 in CFX-Pre)


• Normal Speed• Cartesian Velocity Components• Cylindrical Velocity Components• Mass Flow Rate• Average Static Pressure• Static PressureSee Mass and Momentum (p. 62 in CFX-5 Solver Modelling).

☞ More Help:• Outlet (p. 62 in CFX-5 Solver Modelling)• Outlet (Supersonic) (p. 66 in CFX-5 Solver Modelling)• Outlet (subsonic) (p. 41 in CFX-5 Solver Theory)• Outlet (supersonic) (p. 44 in CFX-5 Solver Theory)• Recommended Configurations of Boundary Conditions (p. 50 in CFX-5

Solver Modelling)

If you use Average Static Pressure when your Domain is Rotating, you can base the pressure averaging on one of:

• Average Over Whole Outlet• Average Above Specified

Radius (enter a radius value)• Average Below Specified

Radius (enter a radius value)• CircumferentialFor stationary domains only Average Over Whole Outlet and Circumferential are available.

See Average Static Pressure (p. 62 in CFX-5 Solver Modelling).

If you are using a radiation model, set one of:

• Adiabatic• Local Temperature• Radiation Intensity: the direction

components of X,Y and Z must be specified.

• External Blackbody Temperature: specify a temperature.

• Radiative Heat Flux: set an inlet flux in [W m^-2].


See Thermal Radiation (p. 60 in CFX-5 Solver Modelling)

Choose a subsonic or supersonic Flow Regime. If supersonic, only the thermal radiation data needs to be set.



Contents Index Help
Boundary Details: Outlet: Multiphase Settings

For a multiphase simulation, the Outlet boundary values are set on the panel below. When the Inhomogeneous model is used and the option is set to Fluid Velocity, then the Fluid Values tab panel is used to set phase-specific velocity data (see Fluid Values: Outlet (p. 291).


• Average Static Pressure• Static Pressure• Degassing Condition (inhomogeneous)• Cartesian Velocity Components

(homogeneous)• Cylindrical Velocity Components

(homogeneous)• Fluid Velocity (inhomogeneous)• Bulk Mass Flow RateIf Average Static Pressure is chosen for a rotating domain, a Pressure Averaging option should be chosen. See Average Static Pressure (p. 62 in CFX-5 Solver Modelling) for more details.

See Mass and Momentum (p. 62 in CFX-5 Solver Modelling) for information on the options available.



Contents Index Help
Boundary Details: Outlet: Mass Flow Settings

Where a mass flow Update Option is chosen, select from the following options.

• Scale Mass Flows• Constant Flux• Shift Pressure (requires a Pressure

Profile and/or Pressure Profile Blend).When a Pressure Profile is chosen, circumferential pressure averaging over a number of circumferential bands can be chosen. See Mass Flow Rate (p. 63 in CFX-5 Solver Modelling) for more details on these options.



Contents Index Help
Boundary Details: OpeningThis panel shows the settings for a single-phase simulation. For other simulation types, please refer to Boundary Details: Opening: Multiphase Settings (p. 281 in CFX-Pre) and Boundary Details: Opening: Additional Variable Settings (p. 282 in CFX-Pre)...

Choices for Mass and Momentum include:

• Cartesian Velocity Components• Cylindrical Velocity Components• Pressure and No Direction

(Entrainment Condition)• Pressure and Direction (stable)• Static PressureSee Mass and Momentum (p. 67 in CFX-5 Solver Modelling).

☞ More Help:

• Opening (p. 67 in CFX-5 Solver Modelling)• Opening (p. 44 in CFX-5 Solver Theory)

If using a variable composition mixture, specify the mass fraction of each of the components at the boundary.

If you are using a radiation model, set either:

• Adiabatic• Local Temperature• Radiation Intensity: the direction

components of X,Y and Z must be specified.

• External Blackbody Temperature: specify a temperature.

• Radiative Heat Flux: set an inlet flux in [W m^-2].


See Thermal Radiation (p. 60 in CFX-5 Solver Modelling)



Contents Index Help
Boundary Details: Opening: Multiphase Settings

See Fluid Values: Inlet/Opening (p. 289) for data that is set on the Fluid Values tab panel.

Choices for Mass and Momentum include:

• Fluid Velocity (when using the Inhomogeneous Model)

• Cartesian Velocity Components (when using the Homogeneous Model)

• Cylindrical Velocity Components (when using the Homogeneous Model)

• Pressure and No Direction (Entrainment Condition)

• Pressure and Direction• Static Pressure• Bulk Mass Flow RateSee Mass and Momentum (p. 67 in CFX-5 Solver Modelling).

☞ More Help:• Opening (p. 67 in CFX-5 Solver

Modelling)• Opening (p. 44 in CFX-5 Solver



Contents Index Help
Boundary Details: Opening: Additional Variable Settings

Boundary Details: WallThe panel below shows the wall settings for a single phase simulation. See also Boundary Details: Wall: Multiphase Settings (p. 284), Boundary Details: Wall: Wall Adhesion

Highlight the Additional Variable to edit, and enter its mass concentration.

For details on Additional Variables, see Additional Variables (p. 19).



Contents Index Help
Settings (p. 284).

Radiation settings must be specified for all radiation models except the algebraic (Rosseland) model.

Radiation options are discussed in Thermal Radiation (p. 75 in CFX-5 Solver Modelling)

Wall influence on flow can be set to No Slip, Free Slip or Counter Rotating Wall (in rotating domains).

Enable U, V and W to set Cartesian components for a moving wall, or leave unchecked to set a stationary wall.

☞ More Help:• Wall (p. 70 in CFX-5 Solver Modelling)• Wall (p. 46 in CFX-5 Solver Theory)• Wall Boundaries in Multiphase (p. 191 in CFX-5 Solver

If using additional variables, select:

• Fluid Dependent Boundary Conditions• Zero Flux• Flux In• Value

When setting Boundary Details for a Wall, the Wall Roughness is required. See Wall Roughness (p. 72 in CFX-5 Solver Modelling).

If heat transfer is modelled, the following options are available for wall modelling:

• Adiabatic• Fixed Temperature• Heat Flux• Heat Transfer CoefficientIf a multiphase simulation is being carried out, you can choose to specify the wall contact model as

• Use Volume Fraction• Specify Area FractionSee Area Contact Model (p. 192 in CFX-5 Solver Modelling). Not applicable to Homogeneous Multiphase.



Contents Index Help
If additional variables exist, they can be set at a wall on a bulk basis if they are present in both fluids and if the Kinematic Diffusivity is set. If Additional Variables are only present in some fluids, or if you select the Fluid Dependent option on the panel below, then the Additional Variable values are set on a per-fluid basis on the Fluid Values panel.

Boundary Details: Wall: Multiphase Settings

See Fluid Values: Wall (p. 292) for data that is set on the Fluid Values tab panel.

Boundary Details: Wall: Wall Adhesion Settings

This part of the panel is used to set the wall contact angle for a free surface flow in which the surface tension force is modelled (Surface Tension Model is set to Continuum Surface Force). This allows wall adhesion effect to be accounted for. See Surface Tension (p. 161 in CFX-5 Solver Theory) for details.

When setting Boundary Details for a Wall, the Wall Roughness is required. See Wall Roughness (p. 72 in CFX-5 Solver Modelling).

If heat transfer is modelled, the following options are available for wall modelling:

• Adiabatic• Fixed Temperature• Heat Flux• Heat Transfer Co-efficient• Fluid Dependent (when using the

Inhomogeneous model)If a multiphase simulation is being carried out, you can choose to specify the wall contact model as:

• Use Volume Fraction• Specify Area FractionSee Area Contact Model (p. 192 in CFX-5 Solver Modelling). Not applicable to

☞ More Help:• Wall (p. 70 in CFX-5 Solver Modelling)• Wall (p. 46 in CFX-5 Solver Theory)• Wall Boundaries in Multiphase (p. 191 in CFX-5 Solver

Modelling)

Set the contact angle that the primary fluid makes with the wall.



Contents Index Help
Boundary Details: Wall: Deposition Settings

This part of the panel is available for dispersed phases using the Algebraic Slip Model. For information on wall deposition, please refer to Wall Deposition (p. 203 in CFX-5 Solver Modelling).

Boundary Details: Wall: Erosion Model

The erosion modelling capability is available when particle tracking is enabled. For details on the available model options, please see Erosion Model (p. 232 in CFX-5 Solver Modelling).

Set the Option to Deposition if wall deposition is to be modelled.

Options available for erosion are:

• None• Finnie (p. 215 in CFX-5 Solver

Modelling)



Contents Index Help
Boundary Details: InterfaceSee Interface Boundary Conditions (p. 264) for an introduction to interface boundaries.

Boundary Details: Interface: Fluid-Solid Interface, Fluid Side

The following panel appears when editing an interface for the fluid side of a Fluid-Solid interface for a single-phase simulation or a homogeneous multiphase simulation (see below for the inhomogeneous case).

If you are using the Particle Tracking model, then a Fluid Values tab panel will also be available where particle options can be set, see Fluid Values: Interface (p. 294).

The default wall roughness is Smooth Wall. You may choose to select a rough wall and enter a roughness height. See Wall Roughness (p. 72 in CFX-5 Solver Modelling).

The Wall Influence on Flow must be No Slip (Free Slip is not allowed). See Wall Influence on Flow (p. 70 in CFX-5 Solver Modelling).

For Heat Transfer, Conservative Interface Flux is the only option.

When radiation is modelled (not available for multiphase), you can use Conservative Interface Flux or the Opaque option, which requires values for Emissivity and Diffuse Fraction. See Opaque (p. 290 in CFX-5 Solver



Contents Index Help
The following panel appears when editing an interface for the fluid side of a Fluid-Solid interface when the inhomogeneous multiphase model is used.

Boundary Details: Interface: Fluid-Solid Interface, Solid Side

The Solid side of the interface uses Conservative Interface Flux for Heat Transfer, if modelled. You may set a Thermal Radiation option, which is the same as the Fluid Side described above. You cannot set any particle options since particles can not exist in a solid domain.

Boundary Details: Interface: Solid-Solid Interface

The Solid sides of the interface uses Conservative Interface Flux for Heat Transfer. You may set a Thermal Radiation option, which is the same as the fluid side of a Fluid-Solid interface, as described above.

Boundary Details: Interface: Fluid-Fluid and Periodic Interfaces

For Periodic and Fluid-Fluid interfaces, Conservative Interface Flux is the only available option for all quantities and cannot be changed.

See Wall Roughness (p. 72 in CFX-5 Solver Modelling).

The Wall Contact Model can be set to Use Volume Fraction (default) or you can specify an area fraction. See Area Contact Model (p. 192 in CFX-5 Solver Modelling).

When heat transfer is modelled, Conservative Interface Flux is the only option available.



Contents Index Help
Symmetry Boundary ConditionsWhen specifying symmetry boundary conditions, select the locations from the drop-down list box and select the Frame Type if your domain is rotating. No further settings are required, and the same settings apply for fluid and solid domains.

Choose the location(s) of the symmetry plane(s) from the list.

When modelling particle transport, see Symmetry Plane Boundaries (p. 234 in CFX-5 Solver



Contents Index Help
Fluid Values

The Fluid Values panels are used to set boundary conditions for each fluid in an Eulerian multiphase simulation and each particle material when Particle Tracking is modelled.

Fluid Values: Inlet/Opening

Fluid Values: Inlet/Opening: Multiphase

This section applies when Static Pressure is set on the Boundary Details tab panel. Select from:

• Normal to Boundary• Directional ComponentsSee Mass and Momentum (p. 55 in CFX-5 Solver Modelling) for details on these

Set Turbulence quantities at the inlet boundary (if applicable). See Turbulence (p. 57 in CFX-5 Solver Modelling) for details.

Set the inlet temperature of each phase (if applicable). See Heat Transfer (p. 59 in CFX-5 Solver Modelling)

This section applies when Fluid Velocity is set on the Boundary Details tab panel. Select from:

• Normal Speed• Cartesian Velocity Components• Mass Flow RateSee Mass and Momentum (p. 55 in CFX-5 Solver Modelling) for details.

Enter the Volume Fraction of the selected Fluid at the inlet. The total Volume Fraction summed over all the fluids must be equal to 1.

If one of the fluids is a variable composition mixture, specify the mass fractions of each of the components. For details, see Boundary Details: Inlet: Variable Composition or Reacting Mixture Settings (p. 275).

Page 289 Fluid Values CFX-5.7.1


Contents Index Help
Fluid Values: Inlet/Opening: Particle Tracking Settings

Select from:

• Normal Speed• Cartesian Velocity Components• Cylindrical Velocity Components• Fluid Flow Rate• Extrapolation• Zero Slip VelocitySee Mass and Momentum (p. 227 in CFX-5 Solver Modelling).

See Particle Diameter Distribution (p. 211 in CFX-5 Solver Modelling).

Select the phase to set properties for.

Optionally specify particle properties at the boundary. When this toggle is disabled, particles do not enter through this boundary.

See Particle Mass Flow Rate (p. 230 in CFX-5 Solver Modelling)

Choose how the particles are injected. See Particle Position (p. 227 in CFX-5 Solver Modelling) and Particle Locations (p. 230 in CFX-5 Solver Modelling)

Available when heat transfer is enabled. See Heat Transfer (p. 231 in CFX-5 Solver Modelling).Available when the particle phase has been set up as a variable composition mixture. See Component Details (p. 231 in CFX-5 Solver Modelling).



Contents Index Help
Fluid Values: OutletIf you are using the inhomogeneous multiphase model and selected the Fluid Velocity option on the Boundary Details tab panel, the fluid-specific velocity information is set on the panel shown below at an outlet boundary.


• Normal Speed• Cartesian Velocity Components• Cylindrical Velocity Components• Mass Flow RateSee Mass and Momentum (p. 62 in CFX-5 Solver Modelling).



Contents Index Help
Fluid Values: WallWhen modelling particle transport, see Fluid Values: Wall: Particle Tracking Settings (p. 293) for wall details.

Set the way in which the wall influences the flow. See Wall Influence on Flow (p. 70 in CFX-5 Solver Modelling).

Select the fluid to set properties for.

Set a Heat Transfer option. See Wall Heat Transfer (p. 72 in CFX-5 Solver

Where additional variables are modelled, set an option for treatment of each one at the wall. See Additional Variables (p. 75 in CFX-5 Solver Modelling).



Contents Index Help
Fluid Values: Wall: Particle Tracking Settings

As well as setting properties for the erosion model, restitution coefficient and mass flow absorption, particles can also be introduced on wall boundaries by enabling Define Particle Behaviour.

See Fluid Values - Restitution Coefficients for Particles (p. 232 in CFX-5 Solver Modelling).

See Erosion Model (p. 232 in CFX-5 Solver Modelling).

Introduce particles into the domain from this boundary. The options available here are the same as described in Fluid Values: Inlet/Opening: Particle Tracking Settings (p. 290)

See Mass Flow Absorption (p. 233 in CFX-5 Solver Modelling).

This option is available when a Particle User Routine (Particle User Routine (p. 181)) has been created. See Wall Interaction (p. 233 in CFX-5 Solver Modelling).



Contents Index Help
Fluid Values: Interface

Fluid Values: Interface: Fluid-Solid Interface, Fluid Side

The following panel is available on the fluid side of a Fluid-Solid interface for an inhomogeneous multiphase setup.

Available when you are using the Inhomogeneous multiphase model. You must use a No-Slip wall, but can set a wall velocity. See Wall Influence on Flow (p. 70 in CFX-5 Solver Modelling).



Contents Index Help
The following form appears when particle transport is enabled, and contains the same options as those that appear for wall boundaries.

Fluid Values: Interface: Fluid-Fluid and Periodic Interfaces

For Periodic and Fluid-Fluid interfaces, Conservative Interface Flux is the only available option for all quantities and cannot be changed.

See Fluid Values - Restitution Coefficients for Particles (p. 232 in CFX-5 Solver Modelling).

See Erosion Model (p. 232 in CFX-5 Solver Modelling).

Introduce particles into the domain from this boundary. The options available here are the same as described in Fluid Values: Inlet/Opening: Particle Tracking Settings (p. 290)

See Mass Flow Absorption (p. 233 in CFX-5 Solver Modelling).



Contents Index Help
Sources

The Sources form is available when the Discrete Transfer or Monte Carlo radiation model is selected. Sources can be specified at Inlet, Opening, Outlet and Wall Boundaries. The Discrete Transfer Model can be used to specify a directional radiation flux.

Click to specify a new radiation source.

More details on Radiation Sources are given in Sources (Discrete Transfer and Monte Carlo models) (p. 61 in CFX-5 Solver Modelling)

Page 296 Sources CFX-5.7.1


Contents Index Help
Mesh Motion

The Mesh Motion tab becomes available when the Mesh Deformation option is set to Regions of Motion Specified on the Basic Settings form for the domain (Mesh Deformation p. 205).

The options available depend on the type of boundary, and will be one of the subset discussed in Mesh Deformation (p. 5 in CFX-5 Solver Modelling).

Page 297 Mesh Motion CFX-5.7.1


Contents Index Help
Plot Options

The Plot Options panel allows you to create Boundary Contour and Boundary Vector graphics to display scalar and vector values at boundaries, respectively.

Boundary Contour

This draws the boundary surface coloured by the selected variable. The available variables depend on the settings on the Boundary Details and Sources panels, as applicable. A Legend appears by default showing the variable plotted on the boundary with a local range. You can turn off visibility for the legend by right-clicking on the Boundary Contour object associated with your boundary condition and toggling the Show Legend option. To access the Boundary Contour object in the Physics Selector, click the + sign to the left of the boundary condition to which it belongs to expand the selector tree for that boundary condition.

Boundary Vector

This draws vectors at the nodes of the boundary surface, pointing in the direction specified by the Profile Vector Component setting. The available vectors depend on the settings on the Boundary Details and Sources panels, as applicable.

Select from one of the available variables using the drop-down list.

Select from one of the available vectors using the drop-down list.

Page 298 Plot Options CFX-5.7.1

Date post:	17-Oct-2014
Category:	Documents
Upload:	jenny-altors
View:	122 times
Download:	7 times

Pre Boundary Conditions

Documents