Preface xiii

**1 Wind Energy and Noise 1**

1.1 Introduction 1

1.2 Development of the Wind Energy Industry 2

1.3 History of Wind Turbine Noise Studies 13

1.4 Current Wind Farm Noise Guidelines and Assessment Procedures 18

1.5 Wind Farm Noise Standards 30

1.6 Regulations 33

1.7 Enquiries/Government Investigations 44

1.8 Current Consensus on Wind Farm Noise 53

References 55

**2 Fundamentals of Acoustics 59**

2.1 Introduction 59

2.2 Basic Acoustics Concepts 59

2.3 Basic Frequency Analysis 82

2.4 Advanced Frequency Analysis 89

2.5 Summary 121

References 122

**3 Noise Generation 123**

3.1 Introduction 123

3.2 Aeroacoustics 125

3.3 Aerodynamic noise generation on wind turbines 131

3.4 Aeroelasticity and Noise 152

3.5 Other Noise Sources 153

3.6 Summary and Outlook 155

References 157

**4 Wind Turbine Sound Power Estimation 161**

4.1 Introduction 161

4.2 Aerodynamic noise prediction 161

4.3 Simple models 162

4.4 Semi-empirical methods (Class II models) 163

4.5 Computational methods (Class III models) 173

4.6 Estimations of Sound Power From Measurements 174

4.7 Summary 182

References 183

**5 Noise propagation 185**

5.1 Introduction 185

5.2 Principles Underpinning Noise Propagation Modelling 186

5.3 Simplest Noise Propagation Models 217

5.4 Danish Low-Frequency Propagation Model 219

5.5 CONCAWE (1981) 220

5.6 ISO9613-2 (1996) Noise Propagation Model 229

5.7 NMPB-2008 Noise Propagation Model 238

5.8 Nord2000 Noise Propagation Model 250

5.9 Harmonoise (2002) Noise Propagation Engineering Model 269

5.10 Required Input Data for the Various Propagation Models 277

5.11 Off-Shore Wind Farm Propagation Models 281

5.12 Propagation Model Prediction Uncertainty 281

5.13 Outside vs Inside Noise at Residences 286

5.14 Vibration Propagation 289

5.15 Summary 294

References 295

**6 Measurement 299**

6.1 Introduction 299

6.2 Measurement of Environmental Noise Near Wind Farms 300

6.3 Vibration 406

6.4 Wind, Wind Shear and Turbulence 408

6.5 Reporting on Noise, Vibration and Meteorological Conditions 417

6.6 Wind Tunnel Testing 423

6.7 Conclusions 439

References 440

**7 Effects of wind farm noise and vibration on people 447**

7.1 Introduction 447

7.2 Annoyance and Adverse Health Effects 452

7.3 Hearing Mechanism 466

7.4 Reproduction of Wind Farm Noise for Adverse Effects Studies 476

7.5 Vibration Effects 478

7.6 Nocebo Effect 479

7.7 Summary and Conclusion 480

References 482

**8 Wind Farm Noise Control 487**

8.1 Introduction 487

8.2 Noise Control by Turbine Design Modification 488

8.3 Optimisation of turbine layout 498

8.4 Options for Noise Control at the Residences 499

8.5 Administrative Controls 503

8.6 Summary 504

References 505

**9 Where to from here 507**

9.1 Introduction 507

9.2 Further Investigation of the Effects of Wind Farm Noise on People 508

9.3 Improvements to Regulations and Guidelines 510

9.4 Propagation Model Improvements 515

9.5 Identification and Amelioration of the Problem Noise Sources on Wind Turbines 516

9.6 Reducing Low-Frequency Noise Levels in Residences 517

References 518

**A Basic mathematics 519**

A.1 Introduction 519

A.2 Logarithms 519

A.3 Complex Numbers 520

A.4 Exponential Function 520

**B The BPM model 521**

B.1 Boundary layer parameters 521

B.2 Turbulent trailing edge noise model 523

B.3 Blunt trailing edge noise model 525

References 527

**C Ground Reflection Coefficient Calculations 529**

C.1 Introduction 529

C.2 Flow Resistivity 530

C.3 Characteristic Impedance 530

C.4 Plane Wave Reflection Coefficient 533

C.5 Spherical Wave Reflection Coefficient 533

C.6 Incoherent Reflection Coefficient 537

References 539

**D Calculation of Ray Path Distances and Propagation Times for the Nord2000 Model 541**

D.1 Introduction 541

D.2 Equivalent Linear Atmospheric Vertical Sound Speed Profile 542

D.3 Calculation of Ray Path Lengths and Propagation Times 544

D.3.1 Direct ray 544

D.3.2 Reflected ray 546

References 549

**E Calculation of Terrain Parameters for the Nord2000 Sound Propagation Model 551**

E.1 Introduction 551

E.2 Terrain Effects 551

E.3 Approximating Terrain profiles by Straight Line Segments 556

E.4 Calculation of the Excess Attenuation Due to the Ground Effect for Relatively Flat Terrain with no Diffraction Edges 558

E.5 Calculation of the Excess Attenuation Due to the Ground Effect for Relatively Flat Terrain with a Variable Impedance Surface and no Diffraction Edges 559

E.6 Calculation of the Excess Attenuation Due to the Ground Effect for Valley-Shaped Terrain 561

E.7 Identification of the Two Most Efficient Diffraction Edges 561

E.8 Calculation of the Sound Pressure at the Receiver for Each Diffracted Path in Hilly Terrain 564

E.9 Calculation of the Combined Ground and Barrier Excess Attenuation Effects 575

References 583

**F Calculation of Fresnel Zone Sizes and Weights 585**

F.1 Introduction 585

F.2 Fresnel Zone for Reflection From Flat Ground 585

F.3 Fresnel Weights for Reflection From a Concave or Transition Ground Segment589

F.4 Fresnel Weights for Reflection from a Convex Ground Segment 591

References 592

**G Calculation of Diffraction and Ground Effects for the Harmonoise Model 593**

G.1 Introduction 593

G.2 Diffraction Effect, _LD 596

G.3 Ground Effect 598

G.3.1 Concave model 600

G.3.2 Transition model 604

G.4 Fresnel Zone for Reflection from a Ground Segment 606

References 610

**H Active Noise Control System Algorithms 611**

H.1 Introduction 611

References 616