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Chapter 18: Modeling Cavitation

This tutorial is divided into the following sections:

18.1.Introduction

18.2.Prerequisites

18.3.Problem Description

18.4.Setup and Solution

18.5.Summary

18.6.Further Improvements

18.1. Introduction

This tutorial examines the pressure-driven cavitating flow of water through a sharp-edged orifice. This is a typical configuration in fuel injectors, and brings a challenge to the physics and numerics of cavitation models because of the high pressure differentials involved and the high ratio of liquid to vapor density. Using the multiphase modeling capability of ANSYS Fluent, you will be able to predict the strong cavitation near the orifice after flow separation at a sharp edge.

This tutorial demonstrates how to do the following:

•Set boundary conditions for internal flow.

•Use the mixture model with cavitation effects.

•Calculate a solution using the pressure-based coupled solver.

18.2. Prerequisites

This tutorial is written with the assumption that you have completed one or more of the introductory tutorial Fluid Flow and Heat Transfer in a Mixing Elbow (p. 35) found in this manual and that you are familiar with the ANSYS Fluent tree and ribbon structure. Some steps in the setup and solution procedure will not be shown explicitly.

18.3. Problem Description

The problem considers the cavitation caused by the flow separation after a sharp-edged orifice. The flow is pressure driven, with an inlet pressure of 5 x 105 Pa and an outlet pressure of 9.5 x 104 Pa. The

orifice diameter is 4 x 10–3 m, and the geometrical parameters of the orifice are D/d = 2.88 and L/d =

4, where D, d, and L are the inlet diameter, orifice diameter, and orifice length respectively. The geometry of the orifice is shown in Figure 18.1: Problem Schematic (p. 630).

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