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Figure 18.1: Problem Schematic

18.4. Setup and Solution

The following sections describe the setup and solution steps for this tutorial:

18.4.1.Preparation

18.4.2.Reading and Checking the Mesh

18.4.3.Solver Settings

18.4.4.Models

18.4.5.Materials

18.4.6.Phases

18.4.7.Boundary Conditions

18.4.8.Operating Conditions

18.4.9.Solution

18.4.10.Postprocessing

18.4.1. Preparation

To prepare for running this tutorial:

1.Download the cavitation.zip file here.

2.Unzip cavitation.zip to your working directory.

3.The mesh file cav.msh can be found in the folder.

4.Use the Fluent Launcher to start the 2D version of ANSYS Fluent.

Fluent Launcher displays your Display Options preferences from the previous session.

For more information about Fluent Launcher, see starting ANSYS Fluent using the Fluent Launcher in the Fluent Getting Started Guide.

5.Ensure that the Display Mesh After Reading option is enabled.

6.Ensure that the Serial processing option is selected.

7.Enable Double Precision.

Note

The double precision solver is recommended for modeling multiphase flows simulation.

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Setup and Solution

18.4.2. Reading and Checking the Mesh

1.Read the mesh file cav.msh.

File → Read → Mesh...

2.Check the mesh.

Domain → Mesh → Check → Perform Mesh Check

3.Check the mesh scale.

Domain → Mesh → Scale...

a.Retain the default settings.

b.Close the Scale Mesh dialog box.

4.Examine the mesh (Figure 18.2: The Mesh in the Orifice (p. 632)).

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Figure 18.2: The Mesh in the Orifice

As seen in Figure 18.2: The Mesh in the Orifice (p. 632), half of the problem geometry is modeled, with an axis boundary (consisting of two separate lines) at the centerline. The quadrilateral mesh is slightly graded in the plenum to be finer toward the orifice. In the orifice, the mesh is uniform with aspect ratios close

to , as the flow is expected to exhibit two-dimensional gradients.

When you display data graphically in a later step, you will mirror the view across the centerline to obtain a more realistic view of the model.

Since the bubbles are small and the flow is high speed, gravity effects can be neglected and the problem can be reduced to axisymmetrical. If gravity could not be neglected and the direction of gravity were not coincident with the geometrical axis of symmetry, you would have to solve a 3D problem.

18.4.3. Solver Settings

1.Specify an axisymmetric model.

Setup → General

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Setup and Solution

a.Retain the default selection of Pressure-Based in the Type list.

The pressure-based solver must be used for multiphase calculations.

b.Select Axisymmetric in the 2D Space list.

Note

A computationally intensive, transient calculation is necessary to accurately simulate the irregular cyclic process of bubble formation, growth, filling by water jet re-entry, and break-off. In this tutorial, you will perform a steady-state calculation to simulate the presence of vapor in the separation region in the time-averaged flow.

18.4.4. Models

1.Enable the multiphase mixture model.

Physics → Models → Multiphase...

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a.Select Mixture in the Model list.

The Multiphase Model dialog box will expand.

b.Clear Slip Velocity in the Mixture Parameters group box.

In this flow, the high level of turbulence does not allow large bubble growth, so gravity is not important. It is also assumed that the bubbles have same velocity as the liquid. Therefore, there is no need to

solve for the slip velocity.

c.Click OK to close the Multiphase Model dialog box.

2.Enable the realizable - turbulence model with standard wall functions.

Physics → Models → Viscous...

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