A comprehensive overview of fluid dynamic models and experimental results that can help solve problems in centrifugal compressors and modern techniques for a more efficient aerodynamic design.
Design and Analysis of Centrifugal Compressors isacomprehensive overview of the theoretical fluid dynamic models describing the flow in centrifugal compressors and the modern techniques for the design of more efficient centrifugal compressors. The author - a noted expert in the field, with over 40 years of experience - evaluates relevant numerical and analytical prediction models for centrifugal compressors with special attention to their accuracy and limitations. Relevant knowledge from the last century is linked with new insights obtained from modern CFD. Emphasis is to link the flow structure, performance and stability to the geometry of the different compressor components.
Design and Analysis of Centrifugal Compressors is an accessible resource that combines theory with experimental data and previous research with recent developments in computational design and optimization. This important resource
- Covers the basic information concerning fluid dynamics that are specific for centrifugal compressors and clarifies the differences with axial compressors
- Provides an overview of performance prediction models previously developed in combination with extra results from research conducted by the author
- Describes helpful numerical and analytical models for the flow in the different components in relation to flow stability, operating range and performance
- Includes the fundamental information for the aerodynamic design of more efficient centrifugal compressors
- Explains the use of computational fluid dynamics (CFD) for the design and analysis of centrifugal compressors
Written for engineers, researchers and designers in industry as well as for academics specializing in the field, Design and Analysis of Centrifugal Compressors offers an up to date overview of the information needed for the design of more effective centrifugal compressors.
Table of Contents
Preface xi
Acknowledgements xiii
List of Symbols xv
1 Introduction 1
1.1 Application of Centrifugal Compressors 2
1.2 Achievable Efficiency 5
1.3 Diabatic Flows 14
1.4 Transformation of Energy in Radial Compressors 19
1.5 Performance Map 25
1.5.1 Theoretical Performance Curve 25
1.5.2 Finite Number of Blades 26
1.5.3 Real Performance Curve 28
1.6 Degree of Reaction 29
1.7 Operating Conditions 32
2 Compressor Inlets 37
2.1 Inlet Guide Vanes 37
2.1.1 Influence of Prerotation on Pressure Ratio 40
2.1.2 Design of IGVs 41
2.2 The Inducer 49
2.2.1 Calculation of the Inlet 50
2.2.1.1 Determination of the Inducer Shroud Radius 51
2.2.2 Optimum Incidence Angle 53
2.2.3 Inducer Choking Mass Flow 56
3 Radial Impeller Flow Calculation 61
3.1 Inviscid Impeller Flow Calculation 63
3.1.1 Meridional Velocity Calculation 63
3.1.2 Blade to Blade Velocity Calculation 66
3.1.3 Optimal Velocity Distribution 68
3.2 3D Impeller Flow 73
3.2.1 3D Inviscid Flow 73
3.2.2 Boundary Layers 76
3.2.3 Secondary Flows 78
3.2.3.1 Shrouded-unshrouded 82
3.2.4 Full 3D Geometries 84
3.3 Performance Predictions 88
3.3.1 Flow in Divergent Channels 88
3.3.2 Impeller Diffusion Model 90
3.3.3 Two-zone Flow Model 94
3.3.4 Calculation of Average Flow Conditions 101
3.3.5 Influence of the Wake/Jet Velocity Ratio 𝜈 on Impeller Performance 102
3.4 Slip Factor 104
3.5 Disk Friction 108
4 The Diffuser 113
4.1 Vaneless Diffusers 116
4.1.1 One-dimensional Calculation 117
4.1.2 Circumferential Distortion 122
4.1.3 Three-dimensional Flow Calculation 125
4.2 Vaned Diffusers 131
4.2.1 Curved Vane Diffusers 131
4.2.2 Channel Diffusers 135
4.2.3 The Vaneless and Semi-vaneless Space 136
4.2.4 The Diffuser Channel 143
5 Detailed Geometry Design 147
5.1 Inverse Design Methods 147
5.1.1 Analytical Inverse Design Methods 148
5.1.2 Inverse Design by CFD 152
5.2 Optimization Systems 156
5.2.1 Parameterized Definition of the Impeller Geometry 157
5.2.2 Search Mechanisms 159
5.2.2.1 Gradient Methods 160
5.2.2.2 Zero-order Search Mechanisms 161
5.2.2.3 Evolutionary Methods 161
5.2.3 Metamodel Assisted Optimization 164
5.2.4 Multiobjective and Constraint Optimization 170
5.2.4.1 Multiobjective Ranking 170
5.2.4.2 Constraints 172
5.2.4.3 Multiobjective Design of Centrifugal Impellers 173
5.2.5 Multipoint Optimization 175
5.2.5.1 Design of a Low Solidity Diffuser 175
5.2.5.2 Multipoint Impeller Design 177
5.2.6 Robust Optimization 181
6 Volutes 185
6.1 Inlet Volutes 185
6.1.1 Inlet Bends 186
6.1.2 Inlet Volutes 190
6.1.3 Vaned Inlet Volutes 193
6.1.4 Tangential Inlet Volute 194
6.2 Outlet Volutes 196
6.2.1 Volute Flow Model 196
6.2.2 Main Geometrical Parameters 197
6.2.3 Detailed 3D Flow Structure in Volutes 200
6.2.3.1 Design Mass Flow Operation 201
6.2.3.2 Lower than Design Mass Flow 204
6.2.3.3 Higher than Design Mass Flow 205
6.2.4 Central Elliptic Volutes 208
6.2.4.1 High Mass Flow Measurements 210
6.2.4.2 Medium and Low Mass Flow Measurements 215
6.2.4.3 Volute Outlet Measurements 215
6.2.5 Internal Rectangular Volutes 215
6.2.5.1 High Mass Flow Measurements 216
6.2.5.2 Medium Mass Flow Measurements 218
6.2.5.3 Low Mass Flow Measurements 219
6.2.6 Volute Cross Sectional Shape 221
6.2.7 Volute Performance 222
6.2.7.1 Experimental Results 224
6.2.7.2 Performance Predictions 225
6.2.7.3 Detailed Evaluation of Volute Loss Model 228
6.2.8 3D analysis of Volute Flow 230
6.3 Volute-diffuser Optimization 231
6.3.1 Non-axisymmetric Diffuser 233
6.3.2 Increased Diffuser Exit Width 234
7 Impeller Response to Outlet Distortion 237
7.1 Experimental Observations 238
7.2 Theoretical Predictions 242
7.2.1 1D Model 244
7.2.2 CFD: Mixing Plane Approach 245
7.2.3 3D Unsteady Flow Calculations 247
7.2.3.1 Impeller with 20 Full Blades 248
7.2.3.2 Impeller with Splitter Vanes 249
7.2.4 Inlet and Outlet Flow Distortion 249
7.2.4.1 Parametric Study 253
7.2.5 Frozen Rotor Approach 254
7.3 Radial Forces 258
7.3.1 Experimental Observations 258
7.3.2 Computation of Radial Forces 263
7.4 Off-design Performance Prediction 267
7.4.1 Impeller Response Model 268
7.4.2 Diffuser Response Model 269
7.4.3 Volute Flow Calculation 269
7.4.4 Impeller Outlet Pressure Distribution 272
7.4.5 Evaluation and Conclusion 273
8 Stability and Range 275
8.1 Distinction Between Different Types of Rotating Stall 276
8.2 Vaneless Diffuser Rotating Stall 280
8.2.1 Theoretical Stability Calculation 284
8.2.2 Comparison with Experiments 287
8.2.3 Influence of the Diffuser Inlet Shape and Pinching 289
8.3 Abrupt Impeller Rotating Stall 296
8.3.1 Theoretical Prediction Models 297
8.3.2 Comparison with Experimental Results 300
8.4 Progressive Impeller Rotating Stall 301
8.4.1 Experimental Observations 301
8.5 Vaned Diffuser Rotating Stall 307
8.5.1 Return Channel Rotating Stall 314
8.6 Surge 314
8.6.1 Lumped Parameter Surge Model 316
8.6.2 Mild Versus Deep Surge 321
8.6.3 An Alternative Surge Prediction Model 325
9 Operating Range 329
9.1 Active Surge Control 330
9.1.1 Throttle Valve Control 331
9.1.2 Variable Plenum Control 333
9.1.3 Active Magnetic Bearings 335
9.1.4 Close-coupled Resistance 336
9.2 Bypass Valves 337
9.3 Increased Impeller Stability 340
9.3.1 Dual Entry Compressors 342
9.3.2 Casing Treatment 344
9.4 Enhanced Vaned Diffuser Stability 347
9.5 Impeller-diffuser Matching 351
9.6 Enhanced Vaneless Diffuser Stability 354
9.6.1 Low Solidity Vaned Diffusers 356
9.6.2 Half-height Vanes 359
9.6.3 Rotating Vaneless Diffusers 359
Bibliography 363
Index 385
