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Contents

Contents

Chaper 1Introduction1

1.1Background & Motivation1

1.2Literature Review of Droplet Impingement Problem2

1.2.1Different Outcomes of Droplet Impingement3

1.2.2Kinetic Processes of Droplet Impingement6

1.2.3Research Progress of High��Speed Droplet

Impingement8

1.2.4Literature Summary11

1.3Flow Mechanics Study of High��Speed Droplet Impingement12

1.3.1Water��Hammer Shock Wave12

1.3.2Evolution of Complex Wave System13

1.3.3Cavitation Phenomena in the Droplet15

1.3.4Erosion of the Impinging Wall16

1.3.5Surface Geometric Effect17

1.4Research of Phase Transition & Cavitation Model18

1.4.1Phase Transition Model18

1.4.2Cavitation Model21

1.5Research Purpose23

Chapter2Mathematical Model & Computational Methodology25

2.1Two��phase Compressible Model25

2.1.1Governing Equations25

2.1.2Mathematical Properties of the Model27

2.1.3Discretization of the Governing Equation28

2.2Physical Parameters Calculation33

2.3Cavitation & Phase Transition Model34

2.3.1Homogeneous/Heterogeneous Nucleation Cavitation

Model34

2.3.2Numerical Simulation of Phase Transition Process36

2.4Numerical Validation40

2.4.1Sod Problem40

2.4.2Two��Phase Shock Tube Problem41

2.4.3Real Cavitation43

2.4.4Spherical Bubble Collapse44

2.5Chapter Summary46

Chapter 3High��speed Droplet Impingement on the Rigid Flat Wall47

3.1Physical Model47

3.2Validation of Numerical Results48

3.2.1Grid Sensitivity Analysis48

3.2.2Comparison With Experimental Results50

3.3Transient Characteristics Inside the Impinging Droplet54

3.3.1The First Stage��Generation and Detachment of

Shock Wave55

3.3.2The Second Stage��Propagation and Reflection of

Shock Wave57

3.3.3The Third Stage��Wave Convergion and Cavitiation

Generation61

3.3.4The Fouth Stage��Cavitation Collapse64

3.4Influence of Initial Velocity66

3.4.1Geometric Properties of Droplets66

3.4.2Size of the Cavitation Zone69

3.4.3Intensity of Collapse Waves70

3.5Influence of Fluid��s Physical Properties72

3.5.1Physical Parameter Fitting72

3.5.2Results Analysis and Discussion73

3.6Chapter Summary78

Chaper 4High��speed Impingement of Droplet Embedded With Cavity80

4.1Physical Model80

4.2Results Comparison of Droplets Embedded With Different

Cavities81

4.2.1Analysis of the Whole Dynamic Processes83

4.2.2Deformation and Collapse Mechanism of Embeding

Cavities88

4.2.3Stress Bearing Analysis of Impinging Wall94

4.3Influence of Cavity Size and Initial Velocity95

4.3.1Collapse Time of Embeding Cavities96

4.3.2Peak Collapse Pressure98

4.3.3Wall Stress Analysis99

4.4Influence of Cavity��s Initial Position101

4.5Chapter Summary104

Chapter 5High��Speed Droplet Impingement on the Rigid Curved Wall106

5.1Physical Model106

5.2Analysis of Confined Shock Waves Under Different Curved

Wall107

5.2.1Generation of Shock Wave107

5.2.2Detachment of Shock Wave110

5.2.3Waveform Evolution114

5.3Cavitation Inside Droplet114

5.3.1Focusing Homogeneous Cavitation115

5.3.2Near��Wall Heterogeneous Cavitation116

5.4Stress Bearing Analysis of Different Curved Wall120

5.5Discussion of Three Dimensional Effect121

5.6Chapter Summary125

Chapter 6Conclutions127

6.1Summary127

6.2Prospect128

References129

Published Academic Papers146

Acknowledgements147