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Setup and Solution

b.In the Mass tab, set Number of Mass Transfer Mechanisms to 1. The dialog box expands to show relevant modeling parameters.

c.Ensure that liquid is selected from the From Phase drop-down list in the Mass Transfer group box.

d.Select vapor from the To Phase drop-down list.

e.Select cavitation from the Mechanism drop-down list.

The Cavitation Model dialog box will open to show the cavitation inputs.

i.Retain the value of 3540 Pa for Vaporization Pressure.

The vaporization pressure is a property of the working liquid, which depends mainly on the temperature and pressure. The default value is the vaporization pressure of water at 1 atmosphere and a temperature of 300 K.

ii.Set the Bubble Number Density to 1e11.

iii.Click OK to close the Cavitation Model dialog box. f. Click OK to close the Phase Interaction dialog box.

4.Close the Phases dialog box.

18.4.7. Boundary Conditions

For the multiphase mixture model, you will specify conditions for the mixture (that is, conditions that apply to all phases) and the conditions that are specific to the primary and secondary phases. In this tutorial, boundary conditions are required only for the mixture and secondary phase of two boundaries: the pressure inlet (consisting of two boundary zones) and the pressure outlet. The pressure outlet is the downstream boundary, opposite the pressure inlets.

Setup → Boundary Conditions

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1.Set the boundary conditions at inlet_1 for the mixture. Ensure that mixture is selected from the Phase drop-down list in the Boundary Conditions task page.

Setup → Boundary Conditions → inlet_1 → Edit...

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Setup and Solution

a.Enter 500000 Pa for Gauge Total Pressure.

b.Enter 449000 Pa for Supersonic/Initial Gauge Pressure.

If you choose to initialize the solution based on the pressure-inlet conditions, the Supersonic/Initial Gauge Pressure will be used in conjunction with the specified stagnation pressure (the Gauge Total Pressure) to compute initial values according to the isentropic relations (for compressible flow) or Bernoulli’s equation (for incompressible flow). Otherwise, in an incompressible flow calculation, ANSYS Fluent will ignore the Supersonic/Initial Gauge Pressure input.

c.Retain the default selection of Normal to Boundary from the Direction Specification Method dropdown list.

d.Select K and Epsilon from the Specification Method drop-down list in the Turbulence group box.

e.Enter 0.02 m2/s2 for Turbulent Kinetic Energy.

f.Retain the value of 1 m2/s3 for Turbulent Dissipation Rate.

g.Click OK to close the Pressure Inlet dialog box.

2.Set the boundary conditions at inlet-1 for the secondary phase.

Setup → Boundary Conditions → inlet_1

a.Select vapor from the Phase drop-down list.

b.Click Edit... to open the Pressure Inlet dialog box.

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i.In the Multiphase tab, retain the default value of 0 for Volume Fraction.

ii.Click OK to close the Pressure Inlet dialog box.

3.Copy the boundary conditions defined for the first pressure inlet zone (inlet_1) to the second pressure inlet zone (inlet_2).

Setup → Boundary Conditions → inlet_1

a.Select mixture from the Phase drop-down list.

b.Click Copy... to open the Copy Conditions dialog box.

i.Select inlet_1 from the From Boundary Zone selection list.

ii.Select inlet_2 from the To Boundary Zones selection list.

iii.Click Copy.

A Question dialog box will open, asking if you want to copy inlet_1 boundary conditions to inlet_2. Click OK.

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Setup and Solution

iv.Close the Copy Conditions dialog box.

4.Set the boundary conditions at outlet for the mixture.

Setup → Boundary Conditions → outlet → Edit...

a.Enter 95000 for Gauge Pressure.

b.Select K and Epsilon from the Specification Method drop-down list in the Turbulence group box.

c.Enter 0.02 m2/s2 for Backflow Turbulent Kinetic Energy.

d.Retain the value of 1 m2/s3 for Backflow Turbulent Dissipation Rate.

e.Click OK to close the Pressure Outlet dialog box.

5.Set the boundary conditions at outlet for the secondary phase.

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