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Summary

In this example, the mesh used is fairly coarse. However, in cavitating flows the pressure distribution is the dominant factor, and is not very sensitive to mesh size.

4.Create and plot a contour definition of the volume fraction of water vapor (Figure 18.6: Contours of Vapor Volume Fraction (p. 655)).

Results → Graphics → Contours → New...

a.Change Contour Name to contour-vf-vapor

b.Enable Filled in the Options group box.

c.Enable Banded in the Coloring group box.

d.Select Phases... and Volume fraction from the Contours of drop-down lists.

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

f.Click Save/Display and close the Contours dialog box.

Figure 18.6: Contours of Vapor Volume Fraction

The high turbulent kinetic energy region near the neck of the orifice in Figure 18.5: Contours of Turbulent Kinetic Energy (p. 654) coincides with the highest volume fraction of vapor in Figure 18.6: Contours of Vapor Volume Fraction (p. 655). This indicates the correct prediction of a localized high phase change rate. The vapor then gets convected downstream by the main flow.

18.5. Summary

This tutorial demonstrated how to set up and resolve a strongly cavitating pressure-driven flow through an orifice, using multiphase mixture model of ANSYS Fluent with cavitation effects. You learned how

to set the boundary conditions for an internal flow. A steady-state solution was calculated to simulate the formation of vapor in the neck of the flow after the section restriction at the orifice. A more 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.

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18.6. Further Improvements

This tutorial guides you through the steps to reach an initial solution. You may be able to obtain a more accurate solution by using an appropriate higher-order discretization scheme and by adapting the mesh. Mesh adaption can also ensure that the solution is independent of the mesh. These steps are demonstrated in Fluid Flow and Heat Transfer in a Mixing Elbow (p. 35).

	Release 2019 R1 - © ANSYS,Inc.All rights reserved.- Contains proprietary and confidential information
656	of ANSYS, Inc. and its subsidiaries and affiliates.