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23.9.8 Defining Multiphase Boundary Conditions

Multiphase boundary conditions are set in the Boundary Conditions panel (Figure  23.9.7), but the procedure for setting multiphase boundary conditions is slightly different than for single-phase models. You will need to set some conditions separately for individual phases, while other conditions are shared by all phases (i.e., the mixture), as described in detail below.

Define $\rightarrow$ Boundary Conditions...

Figure 23.9.7: The Boundary Conditions Panel
figure



Boundary Conditions for the Mixture and the Individual Phases


The conditions you need to specify for the mixture and those you need to specify for the individual phases will depend on which of the three multiphase models you are using. Details for each model are provided below.

VOF Model

If you are using the VOF model, the conditions you need to specify for each type of zone are listed below and summarized in Table  23.9.1.

See Chapter  7 for details about the relevant conditions for each type of boundary. Note that the pressure far-field boundary is not available with the VOF model.


Table 23.9.1: Phase-Specific and Mixture Conditions for the VOF Model
Type Primary Phase Secondary Phase Mixture
exhaust fan;
inlet vent;
intake fan;
outlet vent;
pressure inlet;
pressure outlet;
velocity inlet
nothing volume fraction all others
mass flow inlet mass flow/flux mass flow/flux all others
axis;
fan;
outflow;
periodic;
porous jump;
radiator;
solid;
symmetry;
wall
nothing nothing all others
pressure far-field not available not available not available
fluid mass source;
other porous inputs
mass source;
other porous inputs
porous zone;
porosity;
all others

Mixture Model

If you are using the mixture model, the conditions you need to specify for each type of zone are listed below and summarized in Table  23.9.2.

See Chapter  7 for details about the relevant conditions for each type of boundary. Note that the pressure far-field boundary is not available with the mixture model.


Table 23.9.2: Phase-Specific and Mixture Conditions for the Mixture Model
Type Primary Phase Secondary Phase Mixture
exhaust fan;
outlet vent;
pressure outlet
nothing volume fraction all others
inlet vent;
intake fan;
pressure inlet
coord. system;
flow direction
coord. system;
flow direction;
volume fraction
dir. spec. method;
all others
mass flow inlet mass flow/flux mass flow/flux all others
velocity inlet velocity velocity;
volume fraction
all others
axis;
fan;
outflow (n/a for cavitation model);
periodic;
porous jump;
radiator;
solid;
symmetry;
wall
nothing nothing all others
pressure far-field not available not available not available
fluid mass source;
other porous inputs
mass source;
other porous inputs
porous zone;
porosity;
all others

Eulerian Model

If you are using the Eulerian model, the conditions you need to specify for each type of zone are listed below and summarized in Tables  23.9.3, 23.9.4, 23.9.5, and 23.9.6. Note that the specification of turbulence parameters will depend on which of the three multiphase turbulence models you are using, as indicated in Tables  23.9.4- 23.9.6. See Sections  23.5.10 and 23.12.3 for more information about multiphase turbulence models.

See Chapter  7 for details about the relevant conditions for each type of boundary. Note that the pressure far-field, fan, porous jump, radiator, and mass flow inlet boundaries are not available with the Eulerian model.


Table 23.9.3: Phase-Specific and Mixture Conditions for the Eulerian Model (for Laminar Flow)
Type Primary Phase Secondary Phase Mixture
exhaust fan;
outlet vent;
pressure outlet
(tot. temperature) volume fraction;
gran. temperature
(tot. temperature)
all others
inlet vent;
intake fan;
pressure inlet
coord. system;
flow direction
(tot. temperature)
coord. system;
flow direction;
volume fraction;
gran. temperature
(tot. temperature)
dir. spec. method;
all others
velocity inlet velocity
(tot. temperature)
velocity;
volume fraction;
gran. temperature
(tot. temperature)
all others
axis;
outflow;
periodic;
solid;
symmetry
nothing nothing all others
wall shear condition shear condition all others
pressure far-field;
fan;
porous jump;
radiator;
mass flow inlet
not available not available not available
fluid all source terms;
all fixed values;
other porous inputs
all source terms;
all fixed values;
other porous inputs
porous zone; porosity;
all others


Table 23.9.4: Phase-Specific and Mixture Conditions for the Eulerian Model (with the Mixture Turbulence Model)
Type Primary Phase Secondary Phase Mixture
exhaust fan;
outlet vent;
pressure outlet
(tot. temperature) volume fraction;
gran. temperature
(tot. temperature)
all others
inlet vent;
intake fan;
pressure inlet
coord. system;
flow direction
(tot. temperature)
coord. system;
flow direction;
volume fraction;
gran. temperature
(tot. temperature)
dir. spec. method;
all others
velocity inlet velocity
(tot. temperature)
velocity;
volume fraction;
gran. temperature
(tot. temperature)
all others
axis;
outflow;
periodic;
solid;
symmetry
nothing nothing all others
wall shear condition shear condition all others
pressure far-field;
fan;
porous jump;
radiator;
mass flow inlet
not available not available not available
fluid other source terms;
other fixed values;
other porous inputs
other source terms;
other fixed values;
other porous inputs
source terms for turbulence;
fixed values for turbulence;
porous zone; porosity;
all others


Table 23.9.5: Phase-Specific and Mixture Conditions for the Eulerian Model (with the Dispersed Turbulence Model)
Type Primary Phase Secondary Phase Mixture
exhaust fan;
outlet vent;
pressure outlet
turb. parameters
(tot. temperature)
volume fraction;
gran. temperature
(tot. temperature)
all others
inlet vent;
intake fan;
pressure inlet
coord. system;
flow direction;
turb. parameters;
(tot. temperature)
coord. system;
flow direction;
volume fraction;
gran. temperature
(tot. temperature)
dir. spec. method;
all others
velocity inlet velocity;
turb. parameters
(tot. temperature)
velocity;
volume fraction;
gran. temperature
(tot. temperature)
all others
axis;
outflow;
periodic;
solid;
symmetry
nothing nothing all others
wall shear condition shear condition all others
pressure far-field;
fan;
porous jump;
radiator;
mass flow inlet
not available not available not available
fluid momentum, mass, turb. sources;
momentum, mass, turb. fixed values;
other porous inputs
momentum and mass sources;
momentum and mass fixed values;
other porous inputs
porous zone;
porosity;
all others


Table 23.9.6: Phase-Specific and Mixture Conditions for the Eulerian Model (with the Per-Phase Turbulence Model)
Type Primary Phase Secondary Phase Mixture
exhaust fan;
outlet vent;
pressure outlet
turb. parameters
(tot. temperature)
volume fraction;
turb. parameters;
gran. temperature
(tot. temperature)
all others
inlet vent;
intake fan;
pressure inlet
coord. system;
flow direction;
turb. parameters
(tot. temperature)
coord. system;
flow direction;
volume fraction;
turb. parameters;
gran. temperature
(tot. temperature)
dir. spec. method;
all others
velocity inlet velocity;
turb. parameters
(tot. temperature)
velocity;
volume fraction;
turb. parameters;
gran. temperature
(tot. temperature)
all others
axis;
outflow;
periodic;
solid;
symmetry
nothing nothing all others
wall shear condition shear condition all others
pressure far-field;
fan;
porous jump;
radiator;
mass flow inlet
not available not available not available
fluid momentum, mass, turb. sources;
momentum, mass, turb. fixed values;
other porous inputs
momentum, mass, turb. sources;
momentum, mass, turb. fixed values;
other porous inputs
porous zone;
porosity;
all others



Steps for Setting Boundary Conditions


The steps you need to perform for each boundary are as follows:

1.   Select the boundary in the Zone list in the Boundary Conditions panel.

2.   Set the conditions for the mixture at this boundary, if necessary. (See above for information about which conditions need to be set for the mixture.)

(a)   In the Phase drop-down list, select mixture.

(b)   If the current Type for this zone is correct, click Set... to open the corresponding panel (e.g., the Pressure Inlet panel); otherwise, choose the correct zone type in the Type list, confirm the change (when prompted), and the corresponding panel will open automatically.

(c)   In the corresponding panel for the zone type you have selected (e.g., the Pressure Inlet panel, shown in Figure  23.9.9), specify the mixture boundary conditions.

Figure 23.9.9: The Pressure Inlet Panel for a Mixture
figure

Note that only those conditions that apply to all phases, as described above, will appear in this panel.

figure   

For a VOF calculation, if you enabled the Wall Adhesion option in the Phase Interaction panel, you can specify the contact angle at the wall for each pair of phases as a constant (as shown in Figure  23.9.10) or a UDF (see the UDF manual for more information).

The contact angle ( $\theta_w$ in Figure  23.3.3) is the angle between the wall and the tangent to the interface at the wall, measured inside the phase listed in the left column under Wall Adhesion in the Momentum tab of the Wall panel. For example, if you are setting the contact angle between the oil and air phases in the Wall panel shown in Figure  23.9.10, $\theta_w$ is measured inside the oil phase.

Figure 23.9.10: The Wall Panel for a Mixture in a VOF Calculation with Wall Adhesion
figure

The default value for all pairs is 90 degrees, which is equivalent to no wall adhesion effects (i.e., the interface is normal to the adjacent wall). A contact angle of 45 $^\circ$, for example, corresponds to water creeping up the side of a container, as is common with water in a glass.

(d)   Click OK when you are done setting the mixture boundary conditions.

3.   Set the conditions for each phase at this boundary, if necessary. (See above for information about which conditions need to be set for the individual phases.)

(a)   In the Phase drop-down list, select the phase (e.g., water).

figure   

Note that, when you select one of the individual phases (rather than the mixture), only one type of zone appears in the Type list. It is not possible to assign phase-specific zone types at a given boundary; the zone type is specified for the mixture, and it applies to all of the individual phases.

(b)   Click Set... to open the panel for this phase's conditions (e.g., the Pressure Inlet panel, shown in Figure  23.9.11).

Figure 23.9.11: The Pressure Inlet Panel for a Phase
figure

(c)   Specify the conditions for the phase. Note that only those conditions that apply to the individual phase, as described above, will appear in this panel.

(d)   Click OK when you are done setting the phase-specific boundary conditions.



Steps for Copying Boundary Conditions


The steps for copying boundary conditions for a multiphase flow are slightly different from those described in Section  7.1.5 for a single-phase flow. The modified steps are listed below:

1.   In the Boundary Conditions panel, click the Copy... button. This will open the Copy BCs panel.

2.   In the From Zone list, select the zone that has the conditions you want to copy.

3.   In the To Zones list, select the zone or zones to which you want to copy the conditions.

4.   In the Phase drop-down list, select the phase for which you want to copy the conditions (either mixture or one of the individual phases).

figure   

Note that copying the boundary conditions for one phase does not automatically result in the boundary conditions for the other phases and the mixture being copied as well. You need to copy the conditions for each phase on each boundary of interest.

5.   Click Copy. FLUENT will set all of the selected phase's (or mixture's) boundary conditions on the zones selected in the To Zones list to be the same as that phase's conditions on the zone selected in the From Zone list. (You cannot copy a subset of the conditions, such as only the thermal conditions.)

See Section  7.1.5 for additional information about copying boundary conditions, including limitations.


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