Wind Energy (eBook)

Preface 5
Contents 7
List of Contributors 21
1 Offshore Wind Power Meteorology 32
1.1 Introduction 32
1.2 Offshore Wind Measurements 33
1.3 Offshore Meteorology 33
1.4 Application to Wind Power Utilization 35
1.5 Conclusion 36
References 36
2 Wave Loads on Wind-Power Plants in Deep and Shallow Water 38
2.1 A Concept of Wave Design in Shallow Areas 38
2.2 Deep-Water Wave Data 39
2.3 Wave Transmission into a Shallow Area Using a Phase- Averaging Model 39
2.4 Wave Kinematics 41
2.5 Example of Wave Loads 41
2.6 Wave Transmission into a Shallow Area Using Boussinesq Models 43
2.7 Conclusions 43
2.8 Acknowledgements 43
References 44
3 Time Domain Comparison of Simulated and Measured Wind Turbine Loads Using Constrained Wind Fields 45
3.1 Introduction 45
3.2 Constrained Stochastic Simulation of Wind Fields 45
3.3 Stochastic Wind Fields which Encompass Measured Wind Speed Series 46
3.4 Load Calculations Based on Normal and Constrained Wind Field Simulations 48
3.5 Comparison between Measured Loads and Calculated Ones Based on Constrained Wind Fields 49
3.6 Conclusion 50
References 50
4 Mean Wind and Turbulence in the Atmospheric Boundary Layer Above the Surface Layer 51
4.1 Atmospheric Boundary Layers at Larger Heights 51
4.2 Data from Høvsøre Test Site 52
4.3 Discussion 54
References 55
5 Wind Speed Pro.les above the North Sea 56
5.1 Theory of Inertially Coupled Wind Profiles (ICWP) 56
5.2 Comparison to Observations at Horns Rev and FINO1 58
References 60
6 Fundamental Aspects of Fluid Flow over Complex Terrain for Wind Energy Applications 61
6.1 Introduction 61
6.2 Experimental Setup 62
6.3 Results 63
6.4 Conclusions 66
References 66
7 Models for Computer Simulation of Wind Flow over Sparsely Forested Regions 67
7.1 Introduction 67
7.2 Mathematical Models 67
7.3 Results 68
7.4 Conclusions 70
References 70
8 Power Performance via Nacelle Anemometry on Complex Terrain 71
8.1 Introduction and Objectives 71
8.2 Experimental Installations 71
8.3 Experimental Analysis 71
8.4 Numerical Analysis 72
8.5 Results and Analysis 72
8.6 Conclusion 74
References 75
9 Pollutant Dispersion in Flow Around Bluff - Bodies Arrangement 76
9.1 Introduction 76
9.2 Results of Measurements 77
9.3 Conclusions 79
References 79
10 On the Atmospheric Flow Modelling over Complex Relief 81
10.1 Mathematical Model 81
10.2 Definition of the Computational Case 83
10.3 Conclusion 85
References 85
11 Comparison of Logarithmic Wind Pro.les and Power Law Wind Profiles and their Applicability for Offshore Wind Profiles 86
11.1 Wind Profile Laws 86
11.2 Comparison of Profile Laws 86
11.3 Application to Offshore Wind Profiles 87
11.4 Conclusions 89
References 89
12 Turbulence Modelling and Numerical Flow Simulation of Turbulent Flows 90
12.1 Summary 90
12.2 Introduction 90
12.3 Governing Equations 91
12.4 Direct Numerical Simulation 92
12.5 Statistical Turbulence Modelling 92
12.6 Subgrid Scale Turbulence Modelling 93
12.7 Conclusion 95
References 95
13 Gusts in Intermittent Wind Turbulence and the Dynamics of their Recurrent Times 97
13.1 Introduction 97
13.2 Scaling and Intermittency of Velocity Fluctuations 98
13.3 Gusts for Fixed Time Increments and Their Recurrent Times 98
13.4 The Dynamics of Inverse Times: Times Needed for Fluctuations Larger than a Fixed Velocity Threshold 102
References 103
14 Report on the Research Project OWID – Offshore Wind Design Parameter 104
14.1 Summary 104
14.2 Relevant Standards and Guidelines 104
14.3 Normal Wind Pro.le 105
14.4 Normal Turbulence Model 105
14.5 Extreme Wind Conditions 107
14.6 Outlook 108
14.7 Acknowledgement 108
References 108
15 Simulation of Turbulence, Gusts and Wakes for Load Calculations 109
15.1 Introduction 109
15.2 Simulation over Flat Terrain 109
15.3 Constrained Gaussian Simulation 111
15.4 Wakes 111
References 114
16 Short Time Prediction of Wind Speeds from Local Measurements 115
16.1 Wind Speed Predictions 115
16.2 Prediction of Wind Gusts 117
References 120
17 Wind Extremes and Scales: Multifractal Insights and Empirical Evidence 121
17.1 Atmospheric Dynamics, Cascades and Statistics 121
17.2 Extremes 122
17.3 Discussion and Conclusion 125
References 125
18 Boundary-Layer In.uence on Extreme Events in Stratified Flows over Orography 127
18.1 Introduction 127
18.2 Experimental Procedure 128
18.3 Basic Flow Pattern 128
18.4 Downstream Slip Condition 129
18.5 Boundary Layer and Wave Field Interaction 130
18.6 Concluding Remarks 131
References 131
19 The Statistical Distribution of Turbulence Driven Velocity Extremes in the Atmospheric Boundary Layer – Cartwright/ Longuet-Higgins Revised 132
19.1 Introduction 132
19.2 Model 133
References 135
20 Superposition Model for Atmospheric Turbulence 136
20.1 Introduction 136
20.2 Superposition Model 137
20.3 Conclusions and Outlook 139
References 139
21 Extreme Events Under Low-Frequency Wind Speed Variability and Wind Energy Generation 140
21.1 Introduction 140
21.2 Mathematical Background 141
21.3 Results and Conclusions 142
21.4 Acknowledgments 143
References 143
22 Stochastic Small-Scale Modelling of Turbulent Wind Time Series 144
22.1 Introduction 144
22.2 Consistent Modelling of Velocity and Dissipation 144
22.3 Re.ned Modelling: Stationarity and Skewness 145
22.4 Statistics of the Arti.cial Velocity Signal 147
References 147
23 Quantitative Estimation of Drift and Diffusion Functions from Time Series Data 149
23.1 Introduction 149
23.2 Direct Estimation of Drift and Diffusion 150
23.3 Stability of the Limiting Procedure 151
23.4 Finite Length of Time Series 151
23.5 Conclusion 152
References 153
24 Scaling Turbulent Atmospheric Stratification: A Turbulence/ Wave Wind Model 154
24.1 Introduction 154
24.2 An Extreme Unlocalized (Wave) Extension 155
References 157
25 Wind Farm Power Fluctuations 158
25.1 Introduction 158
25.2 Test Site 159
25.3 PSDs 160
25.4 Coherence 161
25.5 Conclusion 163
References 164
26 Network Perspective of Wind-Power Production 165
26.1 Introduction 165
26.2 Robustness in a Critical-Infrastructure Network Model 165
26.3 Two Wind-Power Related Model Extensions 169
26.4 Outlook 170
References 170
27 Phenomenological Response Theory to Predict Power Output 171
27.1 Introduction 171
27.2 Power Curve from Measurement Data 172
27.3 Relaxation Model 174
27.4 Discussion and Conclusion 175
References 176
28 Turbulence Correction for Power Curves 177
28.1 Introduction 177
28.2 Turbulence and Its Impact on Power Curves 178
28.3 Results 179
28.4 Conclusion 180
References 180
29 Online Modeling of Wind Farm Power for Performance Surveillance and Optimization 181
29.1 Wind Turbine Power Modeling Approach 181
29.2 Measurements and Simulation 182
29.3 Results 183
References 184
30 Uncertainty of Wind Energy Estimation 185
30.1 Introduction 185
30.2 Wind Climate of Hungary 185
30.3 The Uncertainty of the Power Law Wind Pro.le Estimation 187
30.4 Inter-Annual Variability of Wind Energy 187
30.5 Conclusion 188
References 188
31 Characterisation of the Power Curve for Wind Turbines by Stochastic Modelling 190
31.1 Introduction 190
31.2 Simple Relaxation Model 191
31.3 Langevin Method 192
31.4 Data Analysis 192
31.5 Conclusion and Outlook 193
References 194
32 Handling Systems Driven by Di.erent Noise Sources: Implications for Power Curve Estimations 195
32.1 Power Curve Estimation in a Turbulent Environment 195
32.2 Conclusions and Outlook 198
References 198
33 Experimental Researches of Characteristics of Windrotor Models with Vertical Axis of Rotation 199
33.1 Introduction 199
33.2 Experimental Installation and Models 200
33.3 Performance Characteristics of Windrotor Models 200
33.4 Results 202
34 Methodical Failure Detection in Grid Connected Wind Parks 203
34.1 Problem Description 203
34.2 Doubly-fed Induction Generators 203
34.3 Measurements 204
34.4 Conclusions 206
References 206
35 Modelling of the Transition Locations on a 30% thick Airfoil with Surface Roughness 207
35.1 Introduction 207
35.2 Measurements 208
35.3 Modelling 208
35.4 Results and Discussion 209
35.5 Conclusions 211
References 212
36 Helicopter Aerodynamics with Emphasis Placed on Dynamic Stall 214
36.1 Introduction 214
36.2 The Phenomenon Dynamic Stall 215
36.3 Numerical and Experimental Results for the Typical Helicopter Airfoil OA209 216
36.4 Conclusions 218
References 219
37 Determination of Angle of Attack (AOA) for Rotating Blades 220
37.1 Introduction 220
37.2 Determination of Angle of Attack 221
37.3 Numerical Results and Comparisons 222
37.4 Conclusion 224
References 224
38 Unsteady Characteristics of Flow Around an Airfoil at High Angles of Attack and Low Reynolds Numbers 225
38.1 Introduction 225
38.2 Test Facility and Setup 225
38.3 Experimental Results and Discussions 226
38.4 Conclusions 228
References 228
39 Aerodynamic Multi-Criteria Shape Optimization of VAWT Blade Profile by Viscous Approach 229
39.1 Introduction 229
39.2 Physical Model 229
39.3 Blade Profile Optimization 230
39.4 Numerical Results 231
39.5 Conclusion and Prospects 232
References 232
40 Rotation and Turbulence Effects on a HAWT Blade Airfoil Aerodynamics 234
40.1 Introduction 234
40.2 Experiment 234
40.3 Results and Discussion 235
40.4 Conclusion 238
References 238
41 3D Numerical Simulation and Evaluation of the Air Flow Through Wind Turbine Rotors with Focus on the Hub Area 240
41.1 Introduction 240
41.2 Method 241
41.3 Results 241
41.4 Perspective 243
References 243
42 Performance of the Risø-B1 Airfoil Family for Wind Turbines 244
42.1 Introduction 244
42.2 The Wind Tunnel 244
42.3 Results 245
42.4 Conclusions 246
42.5 Acknowledgements 247
References 247
43 Aerodynamic Behaviour of a New Type of Slow-Running VAWT 248
43.1 Introduction 248
43.2 Description of the Savonius Rotors 249
43.3 Description of the Numerical Model 249
43.4 Results 250
43.5 Conclusion 252
References 252
44 Numerical Simulation of Dynamic Stall using Spectral/ hp Method 254
44.1 Introduction 254
44.2 The Spectral/hp Method 255
44.3 The NekTar Code 256
44.4 First Results 257
44.5 Outlook 257
References 257
45 Modeling of the Far Wake behind a Wind Turbine 258
45.1 Extended Joukowski Model 258
45.2 Unsteady Behavior 260
45.3 Conclusions 261
References 261
46 Stability of the Tip Vortices in the Far Wake behind a Wind Turbine 262
46.1 Theory: Analysis of the Stability 262
46.2 Application of the Analysis 264
46.3 Conclusions 264
References 265
47 Modelling Turbulence Intensities Inside Wind Farms 266
47.1 Description of the Model 266
47.2 Comparison of the Model with Wake Measurements 267
47.3 Conclusion 268
References 269
48 Numerical Computations of Wind Turbine Wakes 271
48.1 Numerical Method 271
48.2 Simulation 272
References 275
49 Modelling Wind Turbine Wakes with a Porosity Concept 276
49.1 Introduction 276
49.2 Experimental Set-up 276
49.3 Results for Homogeneous Freestream Conditions 277
49.4 Results for Shear Freestream Conditions 278
49.5 Conclusion 280
References 280
50 Prediction of Wind Turbine Noise Generation and Propagation based on an Acoustic Analogy 281
50.1 Introduction 281
50.2 Problem De.nition 281
50.3 Results 282
References 284
51 Comparing WAsP and Fluent for Highly Complex Terrain Wind Prediction 285
51.1 Introduction 285
51.2 Alaiz Test Site 285
51.3 Description of the Models 286
51.4 Results 286
51.5 Conclusions 289
References 289
52 Fatigue Assessment of Truss Joints Based on Local Approaches 290
52.1 Introduction 290
52.2 Concepts 290
52.3 Examples 293
52.4 Conclusion 294
References 295
53 Advances in Offshore Wind Technology 296
53.1 Introduction 296
53.2 Wind Turbine Technology 296
53.3 Substructure Technology 298
53.4 Installation Methods 299
References 300
54 Beneffts of Fatigue Assessment with Local Concepts 302
54.1 Introduction 302
54.2 Applied Local Concepts 302
54.3 Comparison of Fatigue Design for a Tripod 303
54.4 Conclusion 305
References 305
55 Extension of Life Time of Welded Fatigue Loaded Structures 306
55.1 Introduction 306
55.2 Background 306
55.3 Experimental Studies 307
55.4 Results 307
55.5 Conclusions 309
References 309
56 Damage Detection on Structures of O.shore Wind Turbines using Multiparameter Eigenvalues 310
56.1 Introduction 310
56.2 The Multiparameter Eigenvalue Method 310
56.3 Validation of the Method 312
56.4 Outlook 313
References 313
57 Influence of the Type and Size of Wind Turbines on Anti- Icing Thermal Power Requirements for Blades 314
57.1 Introduction 314
57.2 Analysis of the Results 315
57.3 Anti-Icing Power as a Function of the Machine Size 315
57.4 Anti-Icing Power as a Function of the Machine Type 316
57.5 Conclusions 316
References 317
58 High-cycle Fatigue of “Ultra-High Performance Concrete” and “Grouted Joints” for O.shore Wind Energy Turbines 318
58.1 Introduction 318
58.2 Ultra-High Performance Concrete 318
58.3 Ultra-High Performance Concrete in Grouted Joints 319
58.4 Conclusions 320
References 321
59 A Modular Concept for Integrated Modeling of O . shore WEC Applied to Wave- Structure Coupling 322
59.1 Introduction 322
59.2 Integrated Modeling 322
59.3 Modeling of Wave Loads on the Support Structure Offshore Wind Energy Turbines 325
59.4 Future Demands 326
References 326
60 Solutions of Details Regarding Fatigue and the Use of High-Strength Steels for Towers of Offshore Wind Energy Converters 327
60.1 Introduction 327
60.2 Fatigue Tests 328
60.3 Finite-Element Analyses 329
References 332
61 On the Influence of Low-Level Jets on Energy Production and Loading of Wind Turbines 333
61.1 Introduction 333
61.2 Data and Methods 333
61.3 Results 334
61.4 Conclusions 335
References 336
62 Reliability of Wind Turbines 337
62.1 Introduction 337
62.2 Data Basis 337
62.3 Break Down of Wind Turbines 338
62.4 Malfunctions of Components 339
62.5 Conclusion 340
References 340

1 Offshore Wind Power Meteorology (p. 1-2)

Bernhard Lange

Summary. Wind farms built at offshore locations are likely to become an important part of the electricity supply of the future. For an efficient development of this energy source, in depth knowledge about the wind conditions at such locations is therefore crucial. Offshore wind power meteorology aims to provide this knowledge. This paper describes its scope and argues why it is needed for the efficient development of offshore wind power.

1.1 Introduction

Wind power utilization for electricity production has a huge resource and has proven itself to be capable of producing a substantial share of the electricity consumption. It is growing rapidly and can be expected to contribute substantially to our energy need in the future (GWEC, 2005). The ‘fuel’ of this electricity production is the wind. The wind is, on the other hand, also the most important constraint for turbine design, as it creates the loads the turbines have to withstand.

Therefore, accurate knowledge about the wind is needed for planning, design and operation of wind turbines. Some tasks where speci.c meteorological knowledge is essential are wind turbine design, resource assessment, wind power forecasting, etc. Wind power meteorology has therefore established itself as an important topic in applied meteorology (Petersen et al., 1998). For wind power utilization on land, substantial knowledge and experience has been gained in the last decades, based on the detailed meteorological and climatological knowledge available. Offshore, the meteorological knowledge is less developed since there has been little need to know the wind at heights of wind turbines over coastal waters and any measurements at offshore locations are di.cult and extremely expensive.

The aim of this paper is to describe the scope of offshore wind power meteorology and to argue why this topic should be given more attention both from the meteorological point of view and from the wind power application point of view. The paper is structured in three main sections: First some particular problems of offshore measurements are discussed in Sect. 1.2. This is followed by a section giving examples for meteorological effects specific for offshore conditions. Their importance for wind power application is shown in Sect. 1.4, followed by the conclusion.

1.2 Offshore Wind Measurements

In recent years, measurements with the aim to determine the wind conditions for offshore wind power utilization have been erected at a number of locations (Barthelmie et al., 2004). Offshore wind measurements are a challenging task, not only since an offshore foundation and support structure for the mast are needed, but also because of the challenges to provide an autonomous power supply and data transfer, the difficulties of maintenance and repair in an offshore environment, etc. These difficulties lead to high costs of offshore measurements and often lower data availability compared to locations on land. Additionally, the flow distortion of the self supporting mast usually requires a correction of the measured wind speeds for wind profile measurements (Lange, 2004).

Two measurements, from which results are shown in this paper, are the Rødsand field measurement in the Danish Balitc Sea and the FINO 1 measurement in the German Bight.