Cavitation Instabilities and Rotordynamic Effects in Turbopumps and Hydroturbines (eBook)

Preface 6
Contents 8
1 An Introduction to Cavitation in Inducers and Turbopumps 10
Abstract 10
1 General Aspects of Cavitation 10
2 Cavitation Nuclei 11
3 Forms and Occurrence of Cavitation 13
4 Classical Theory of Cavitation Scaling 13
5 Cavitation and Bubble Dynamics 15
6 Thermal Cavitation Effects 17
7 Steady Cavitation in Turbomachines 22
8 Flow-Induced Instabilities in Turbomachines 25
9 Flow Stability of Pumping Systems 27
10 Flow Stability of Cavitating Turbopump Systems 31
11 Conclusions 36
References 37
Experimental Methods for the Study of Hydrodynamic Cavitation 43
1 Introduction 43
2 Characterization and Management of Water Quality 45
2.1 Dissolved Gas Content 46
2.2 Free Gas Content and Cavitation Nuclei 47
2.3 Direct Measurement of the Cavitation Nuclei Distribution 48
2.4 Indirect Measurement of the Cavitation Nuclei Distribution 49
2.5 Management of Water Quality 50
3 Detection and Measurement of Incipient Cavitation 51
3.1 Detection of Inception with Acoustic, Vibration, and Force Measurements 52
3.2 Optical Measurement and Light Scattering for Inception Detection 54
4 Optical Measurement of the Cavitating Flow Field 54
4.1 High-Speed Imaging 55
4.2 Laser Doppler Velocimetry and Light Scattering Methods 55
4.3 Particle Imaging Velocimetry 58
5 Measurement of Cavity Flows with High Void Fraction 61
5.1 Surface Pressure, Acceleration, and Forces 61
5.2 Electrical Impedance Probes 61
5.3 Fiber Optic Probes 63
5.4 Ionizing Radiation 63
References 67
3 An Introduction to Flow-Induced Instabilities in Rocket Engine Inducers and Turbopumps 73
Abstract 73
1 Introduction 73
2 Rotating Stall 77
3 Rotating Cavitation 78
4 Other Rotating Instabilities 80
5 Cavitation Surge 84
6 Higher Order Cavitation Instabilities 86
7 Conclusions and Perspectives 89
References 90
4 Three-dimensional Simulation of Cavitation Instabilities 95
1 Three-Dimensional Simulation of Cavitation Instabilities 95
1.1 Simulation of Alternate Blade Cavitation (Kang et al. 2009a) 95
1.2 Simulation of Rotating Cavitation 99
2 Suppression of Rotating Cavitation Using a Circumferential Groove on the Casing 101
2.1 Design of Circumferential Grooves 102
2.2 Flow Characteristics 102
2.3 Experimental Results 105
2.3.1 Non-cavitating Performance 105
2.3.2 Suction Performance 106
2.3.3 Cavitation Instabilities 106
2.3.4 Cavity Geometry 108
2.3.5 Propagation of Backflow Vortex Cavity 109
2.4 Cause of Higher Frequency Oscillations 110
2.4.1 Unsteady Calculation 110
2.4.2 Rotating Modes Due to Interaction 111
3 Conclusions 114
Acknowledgements 115
5 Rotordynamics of Turbopumps and Hydroturbines 116
1 Introduction 116
2 Example of Forced and Self-Excited Vibrations in Pumps 117
3 Effects of Rotordynamic Force and Moment on Rotordynamic Instability 120
4 Rotordynamic Forces on Centrifugal Impellers 122
4.1 Two-Dimensional Impeller in a Vaneless Space 123
4.2 Interaction with Volutes and Vaned Diffusers 125
4.3 Rotordynamic Forces on the Shroud 127
4.4 Rotordynamic Problem in a Rocket Turbopump 131
5 Rotordynamic Problems in Hydraulic Turbines 133
5.1 Rotordynamic Fluid Force Moment 136
5.2 Moment Whirl 137
5.3 Examples of Vibrations in a Large Pump and a Hydraulic Turbine 139
6 Conclusion 141
References 141
6 On the Preliminary Design and Performance Prediction of Centrifugal Turbopumps—Part 1 144
Abstract 144
1 Introduction 145
2 Turbopump Flow and Geometry 149
2.1 Impeller Flow and Geometry 150
2.2 Diffuser Flow and Geometry 154
2.3 Volute Flow and Geometry 154
3 Turbopump Performance 156
4 Model Discussion 157
5 Conclusions 160
References 161
7 On the Preliminary Design and Performance Prediction of Centrifugal Turbopumps—Part 2 164
Abstract 164
1 Introduction 165
2 Hydraulic Losses and Efficiency 166
2.1 Impeller 167
2.2 Diffuser 174
2.3 Volute 175
2.4 Overall Performance 176
3 Experimental Apparatus 176
4 Results and Discussion 179
5 Conclusions 183
References 183
Numerical Simulation of Cavitating Flows with Different Cavitation and Turbulence Models 186
1 Introduction 186
2 The 1-Fluid Inviscid Formulation 188
2.1 The Conservations Laws 189
2.2 The Pure Phases EOS 189
2.3 Mixture EOS 190
2.4 A Void Ratio Transport-Equation Model 191
2.5 Other Formulations for the Void Ratio Equation 192
3 The Thermal Effects Modelling 193
3.1 A Mixture of Stiffened Gas EOS 193
3.2 A Modified Sinusoidal EOS 194
3.3 A Void Ratio Transport-Equation Model 195
4 The 1-Fluid RANS Formulation 195
4.1 The Mixture Conservation Laws 195
4.2 Mixture Turbulence Equations for Two-Phase Flows 197
4.3 Turbulence Models 198
4.4 Eddy Viscosity Limitation 199
4.5 Scale-Adaptive Simulation 200
4.6 Wall Functions 201
5 The 1-Fluid Filtered Formulation 202
6 The Cavitation Software CaviFlow 204
6.1 Spatial Discretization 204
6.2 The Low Mach Number Preconditioner 204
6.3 Temporal Discretization 205
6.4 Inlet and Outlet Boundary Conditions 205
7 Test Cases Used for the Numerical Studies 206
7.1 Water--Gas Mixture Expansion Tube at Different Velocities 206
7.2 Venturi Data in Cold Water 207
7.3 Venturi Data in Freon R-114 209
8 Comparison of Turbulence Models 210
8.1 Eddy Viscosity Limitation 210
8.2 Compressibility Effects 213
8.3 Wall Models and Near-Wall Mesh 214
8.4 Scale-Adaptive Simulation 217
8.5 Concluding Remarks 219
9 Comparison of Cavitation Models 219
9.1 Inviscid Tube Cases 219
9.2 4° Venturi Case 222
9.3 8° Venturi Case 226
10 Cavitation Models and Thermodynamic Effects 231
10.1 Inviscid Tube Cases 231
10.2 Venturi Case with Freon R-114 232
11 Conclusion and Perspectives 235
References 236
Numerical Simulation of Cavitating Flows in Complex Geometries 241
1 Introduction 241
2 Governing Equations and Cavitation Modeling 243
3 Numerical Methodology 246
3.1 Numerical Discretization for a 1D Inviscid Flow 247
3.2 Extension to 3D URANS Equations in a Rotating Frame 253
4 Application to the Flow in a Turbopump Inducer 257
5 Concluding Remarks 262
References 263
From Cavitating to Boiling Flows 265
1 Introduction 265
2 Basic Flow Model Specification 267
2.1 Equations of State 270
3 Kinetic Relaxation Rate---Thermo-Chemical Relaxation Solver 275
4 Hyperbolic Solver 278
5 Cavitating Flows 281
6 Boiling Flows 283
7 Conclusions 286
References 287