Handbook of Wind Energy Aerodynamics

Preface
Contents
About the Editors
Contributors
1 The Issue of Aerodynamics in Wind Energy
Contents
Introduction
Blade Design
Model Issues
Measuring Wind Turbine Aerodynamics
Wind and Aerodynamics
Wind Turbine or Wind Farm Aerodynamics?
Alternative Concepts
Acoustics of Wind Turbines
Conclusion
References
Part I Aerodynamic Blade Design
2 Economic Aspects of Wind Turbine Aerodynamics
Contents
Introduction
LCoE as a Design Driver for Wind Turbines
LCoE Definition and Target Values
LCoE Contributors (AEP, CAPEX, OPEX) Onshore/Offshore. Turbine (Subsystems Level), Balance of Plant, and Operation and Maintenance Parts
LCoE Evaluation Using Cost Models
The Critical Role of Increasing AEP in LCoE Reduction, Especially Offshore
LCoE Evolution with Technology Maturity, Learning Curve, and Short-/Mid-/Long-Term Target Values
LCoE and Turbine Size and Architecture (Emphasis on Rotors)
Turbine Architectures
LCoE, Upscaling, and Optimum Turbine Size
Upscaling and AEP
Upscaling and CAPEX
Upscaling and OPEX
Upscaling and Land/Area Requirements
Optimal Turbine Size
Tendencies in Onshore/Offshore Rotor Designs. Impact of Larger and Lower Power Densities, Cpmax, and Lower Induction Designs
Exploring Passive and Active Load Alleviation Techniques to Increase Rotor Size and AEP or Reduce CAPEX
Rotor Aerodynamics and LCoE Reduction
Rotor Aerodynamics and AEP
Rotor Aerodynamics and CAPEX
LCoE Reduction Potential Through Innovative and Advanced Aerodynamic Design
Cross-References
References
3 The Actuator Disc Concept
Contents
Introduction
The Actuator Disc
From Actuator Disc to Rotor Aerodynamics
Force Fields in Rotor Aerodynamics
Force Fields: Output from or Input in the Equation of Motion?
Equivalence of the Kinematic and Dynamic Methods
The Equation of Motion and the Coordinate Systems
Non-conservative and Conservative Force Fields
The Disc as Representation of a Rotor
The Actuator Disc Equation
Power and Thrust Expressions of Joukowsky Discs and Rotors
Analysis of Froude Actuator Disc Flows
The Momentum Balance
Momentum Theory Without Conservative Forces
Momentum Theory Including Conservative Forces
Numerical Assessment of Actuator Disc Performance
Flow and Pressure Patterns
Properties of the Wake Boundary
Pressure at the Axis
The Velocity Distribution at the Disc
The Momentum Balance Per Annulus
An Engineering Model for the Velocity at the Disc
Analysis of Joukowsky Actuator Disc Flows
The Equations for a Disc with Torque and Swirl
Momentum Theory for Joukowsky Discs
Limit Values: λ→∞, λ→0,Cp,max
Numerical Results
The Momentum Balance Per Annulus of Joukowksy Disc Flows
The Role of Swirl
On the Use of Actuator Disc Theory in BEM
Blade and Tip Effects
Comparison of Actuator Disc and BEM Induction
Cross-References
References
4 Airfoil Design
Contents
Nomenclature
Introduction
How to Measure the Performance
Rotor Performance
Airfoil Performance
Prediction Methods
Panel Methods
CFD
Design Methods
The Design Problem
Object Functions
Design Variables
Constraints
An Example of a Design
Setup of the Optimization Problem
Design Variables
Flow Prediction
Objective Function
Constraints
Optimization Algorithm
Results
Summary
Outlook
References
5 Rotor Blade Design, Number of Blades, Performance Characteristics
Contents
Introduction
Theoretical Design
Practical Design
Optimised Design
Cost Function
Design Variables
Constraints
Optimisation Method
Models
Results
Other Design Variables
How Many Blades?
Blade Axis Geometry
Advances
Cross-References
References
6 Blade Design with Passive Flow Control Technologies
Contents
Introduction
Static Concepts
Vortex Generators
Introduction
Flow Separation Control
Vortex Generators and Integrated Design
Wind Turbine Integration
Concluding Remarks
Static Miniflaps
Introduction
State of the Art
Performance Optimization of Wind Turbines
Concluding Remarks
Root Spoilers
Introduction
Root Spoiler Design
Effect of Root Spoiler Implementation for the Root Section (t/c=66%)
Effect of Root Spoiler Implementation for the Tip Section (t/c=21%)
Concluding Remarks
Serrations
Introduction
Wind Turbine Noise
The TBL-TE Noise Mechanism
Trailing Edge Serrations
Concluding Remarks
Dynamic Concepts
Passive Flaps
Background and State of the Art
Description of Passive Flap Technology
Performance Optimization of Wind Turbines with Passive Flaps
Concluding Remarks
Aeroelastic Coupling
Introduction
Geometric Coupling
Material Coupling
Concluding Remarks
Integration of Passive Flow Control Technologies into the Design Process of Wind Turbines
Conclusions
Cross-References
References
Part II Aerodynamic Modeling Techniques
7 History of Aerodynamic Modelling
Contents
Introduction
Aerodynamic Modelling of Wind Turbines: An Exciting Story of Its Development and Technology
Historic Development in Windmills with Emphasis on the Aerodynamics
Development of the First Aerodynamic Theories for Design and Performance of Wind Turbines
Drag Device Modelling
Momentum Theory
The Navier-Stokes Equation
Actuator Disk Theory
Potential Flow Theory/Vortex Modelling
BEM Development
The Emergence of Lift-Driven VAWTs
The Number of Blades Issue
Dedicated Aerfoil Designs for Wind Turbine Applications
Yawed Flow Aerodynamics, Shear Flow Modelling, and Wind Farm Aerodynamics
Wind Turbine Augmentation Principles and Devices
Cross-References
References
8 Interacting Boundary Layer Methods and Applications
Contents
Introduction
Governing Equations
Boundary Layer Approximation
Some Remarks on Three-Dimensional Effects
Integral Boundary Layer Equations
Eigenvalues of the Laminar System
Laminar to Turbulent Transition
Closure Set
Laminar Closure Set
Turbulent Closure Set
Inviscid Flow
Numerical Solutions of IBL Equations with Prescribed Boundary Conditions
Similarity Solutions
Laminar and Turbulent Flow Over a Flat Plate
Laminar Flow Over a Cylinder
Flow Over Airfoil Sections
Viscous-Inviscid Interaction
Numerical Solutions for Interacting Boundary Layers
Flow Over Airfoil Sections
Limitations of Interacting Boundary Layer Methods
Drag and Lift Correction
Double Wake Implementation
Future Work
References
9 CFD Simulations for Airfoil Polars
Contents
Introduction
Solution Approaches
Grid Characteristics
Effects of Turbulence Models
Near and Post-stall Characteristics
Transition
Reynolds Number Effects
Conclusions
Cross-References
References
10 Dynamic Stall
Contents
Introduction
Physical Phenomenon Description
Occurrence of Dynamic Stall
Influence of Operational Parameters on Dynamic Stall Behaviour
Dynamic Stall on Wind Energy Machines
Dynamic Stall on HAWT
Dynamic Stall on VAWT
Experimental Data on Dynamic Stall
Dynamic Stall Modelling
Beddoes-Leishman Type of Dynamic Stall Modelling
Modelling Dynamic Stall in Wind Energy Machines
Cross-References
References
11 Thick Sections
Contents
Introduction and General Aspects
Development Challenges
Design Challenges
Modeling Challenges
Wind Tunnel Testing Challenges
Conclusions
References
12 The Effect of Add-Ons on Wind Turbine Blades
Contents
Introduction
Selection of Add-Ons
Vortex Generators
Gurney Flaps
Winglet
Noise Reduction from Serrated Trailing Edge (STE)
Design Parameters
Attachment of the STE
Noise Reduction Effect of the STE on the Blade
References
13 Pragmatic Models: BEM with Engineering Add-Ons
Contents
Definition and the Need for Engineering Models in Rotor Aerodynamics
Description of Blade Element Momentum Theory
Axial Momentum Theory
Blade Element Theory
Axial Blade Element Momentum Theory
Tangential Blade Element Momentum Theory
Uncertainties and Assumptions in BEM Theory
2D (Basic) Airfoil Data
Assumption of Incompressible Flow
Assumption of Inviscid Flow
Assumption of Annular Independency, Axi-Symmetry
Shear and Turbulence
Assumption of Actuator Disc Concept
Turbulent Wake
Assumption of Stationary Conditions
Unsteady Airfoil Aerodynamics
Dynamic Inflow
Assumption of 2D Airfoil Aerodynamics
Yawed Flow
Cone Angle, Tilt Angle, and Unconventional Blade Shapes
Tower Effects
Assessment of Engineering Methods
References
14 CFD for Wind Turbine Simulations
Contents
Introduction
Simulation Methods
RANS
URANS
DES Family
LES
Observations
Numerical Setups
Domain Topology and Size
Discretization Schemes
Boundary Conditions
Uniform Inflow
Nonuniform Inflow
QOI and Post-processing
Grid Requirements
Grid Convergence Index
Requirements for Transitional Turbulence Models
DES Grid Requirements
LES Grid Requirements
Turbulence Models
Spalart–Allmaras
k-ωSST
γ-Reθt
Linear Stability Theory with RANS
Observations
Examples of Application
Mexico and MexNext Experiment
NREL Phase VI Experiment
Validation Against Field Experiments
DAN-AERO MW Experiment
Validation for Virtual Models
NREL 5MW
DTU 10MW
AVATAR
Derivation of Engineering Models
Estimation of the Angle of Attack
Derivation of Root and Tip Models
Derivation of Rotational Augmentation Models
Cross-References
References
15 Aeroelastic Simulations Based on High-Fidelity CFD and CSD Models
Contents
Abbreviations
Introduction
State-of-the Art of CFD-Based Simulation of Wind Turbine Aeroelasticity
State of the Art of Wind Turbine Aeroelasticity Modeling
Blade Instabilities
Rotor/Tower Coupling Instabilities
Flutter
Aeroelastic Models
Wind Turbine Aerodynamic Models
Wind Turbine Structural Models
Modal Shape Function
Multi-Body Dynamics
Finite Element Method
Flow Solver: Modeling and Simulation Techniques
Load Integration
Mesh Deformation Approaches
Point-by-Point Schemes
RBF Approach
Mesh Connectivity-Based Schemes
Spring Analogy Approach
Elliptic Smoothing Approach
Elastic Analogy Approach
Hybrid Schemes
Navier-Stokes-Based CFD with Large Deformations and Surface Motion
Treatment of Flows with Changing Boundaries: ALE with Mesh Moving and Embedded Techniques
Immersed Boundaries
Embedded Boundaries
Arbitrary Lagrangian-Eulerian (ALE) Method
ALE-Variational Multiscale Methods (VMS)
Approaches to Deal with Rotating Components
Temporal and Spatial Resolution for FSI Simulations
Structural Solver: Modeling and Simulation Techniques
High-Fidelity FE Structural Models for Wind Turbines
Governing Equations
Numerical Discretization
Element Types
Solid Elements
Shell Elements
Beam Elements
Application of High-Fidelity CSD FE Models to Wind Turbines
Obtaining Beam Sectional Data from Higher Dimensionality Models
List of Input Data Required by Beam Elements
Aspects of Computational Fluid-Structure Interaction
Nonmatching Grid Treatment
Special Aspects of Dimensionally Reduced Structural Models
Interface Coupling Conditions
Coupling Schemes
Communication Patterns
Jacobi Pattern
Gauss-Seidel Pattern
Weak and Strong Coupling Methods
Weak/Explicit/Loose/Staggered Coupling Algorithm
Strong/Implicit/Iterative Coupling Algorithm
Overall Procedures for High-Fidelity Wind-Structure Interaction Simulations
Simulation Results
Flow Solver FLOWer
Structure Solver Carat ++
Co-Simulation Environment EMPIRE
Wind Turbine Configuration
Blade Structural Properties
CFD Setup
CSD Setup
Blade Modeled by Beam Elements
Blade Modeled by Shell Elements
Effects of the Structural Models
Conclusions and Recommendations
Cross-References
References
16 Aeroelastic Stability Models
Contents
Introduction
Aeroelasticity
Wind Turbine Aeroelasticity
Wind Turbine Modes
Campbell Diagram
Harmonic Components in Modes
Instabilities
Helicopter Aeroelasticity
Instability or Resonance
Stall-Induced Vibrations
Edgewise and Flapwise Instabilities
Idling Instabilities
Vortex-Induced Vibrations
Classical Flutter
Theoretical Background
Determine Flutter Speed
Aeroelastic Evaluations
Linearised Analysis Tools
Using Nonlinear Time Domain Simulation Tools
Measurements
Tool Demands
Aeroelastic Design and Innovations
Aeroelastic Design
Innovations
Conclusions
Cross-References
References
Part III Experimental Approaches to Wind TurbineAerodynamics
17 Wind Tunnel Wall Corrections for Two-Dimensional Testing up to Large Angles of Attack
Contents
Introduction
Blockage in Attached Flow
General Form
Solid and Wake Blockage
Solid Blockage
Wake Blockage
The Total Blockage Factor
Wake Buoyancy
Lift Interference
Overview of Corrections on Coefficients for Streamlined Flow
Correction of the Pressure Distribution
Correction of Measurements in the Deep-Stall Region
Maskell's Method
Corrections on Drag
Two-Dimensional Models
Correction on the Angle of Attack
Corrections on Lift and Moment Coefficients
Higher Values of c/h
The Wall Pressure Signature Method
The Source-Source-Sink Method
The Matrix Version of the Wall Signature Method
Data Accuracy
Summary
References
18 Examples of Wind Tunnels for Testing Wind Turbine Airfoils
Contents
Why Wind Tunnel Testing Is Required for Wind Turbine Airfoils?
The Most Important Requirements of a Wind Tunnel to Be Suitable for Airfoil Testing
Wind Tunnels for Wind Turbine Airfoil Testing
Wind Tunnels Used but That Are Not Available/Used Anymore
NASA Langley Low-Turbulence Pressure Tunnel (LTPT)
Velux Wind Tunnel
Examples of Wind Tunnels
TU Delft Low-Turbulence Tunnel (LTT)
Virginia Tech Stability Wind Tunnel (VTSWT)
Deutsche WindGuard Aeroacoustic Wind Tunnel (DWAA)
University of Stuttgart Laminar Wind Tunnel
Poul la Cour Tunnel
LM Wind Power Low-Speed Wind Tunnel (LSWT)
HDG High-Pressure Wind Tunnel of Gottingen
Texas A&M University Low-Speed Wind Tunnel (LSWT)
Ohio State University 35 Subsonic Wind Tunnel
DNW-KKK Cryogenic Wind Tunnel
The Cranfield University Icing Wind Tunnel
Prospects of Wind Tunnel Setups for Airfoil Testing
Cross-References
References
19 Wind Tunnel Rotor Measurements
Contents
Introduction
Historical Overview
Motivation
Several Large Experiments and Their Challenges
Joint FFA and CARDC Experiments
NREL UAE Phase VI Experiment
Mexico and New Mexico Experiments
Comparison Rounds and IEA Tasks
Future Perspective
Innovative Measurement Techniques
Closing the Gap Between Field and Wind Tunnel Measurements
Cross-References
References
20 3D Wind Tunnel Experiments
Contents
Introduction
A Review of the Most Significant Turbine Model Experiments
Samples of Turbine Scale Model Technology
Aerodynamic Design
Structural Components
Actuation Capabilities
Typical Measurements
Hybrid Experiments in Floating Wind Turbines
Cross-References
References
21 Corrections and Uncertainties
Contents
Introduction
Measurements in General
Quality Guidelines for Wind Tunnel Measurements
2D Wind Tunnel Measurements
3D Wind Tunnel Measurements on Wind Turbines
Classical Wind Tunnel Corrections from Textbooks
Wind Tunnel Corrections from CFD
NREL Unsteady Aerodynamics Experiment (UAE, 2000)
Summary and Conclusion
Cross-References
References
22 Doppler Lidar Inflow Measurements
Contents
Nomenclature
Introduction to Inflow Measurements
In Situ Inflow Measurements
Remote Sensing Measurements
Introduction to Doppler Lidar
Principles of Continuous-Wave Lidar
Principles of Pulsed Lidar
Comparison Between Continuous-Wave and Pulsed Lidar
Multiple-Doppler Lidar
Applications of Doppler Lidar
Vertical Profiling
Lidar for Power Curve Measurement
Turbulence Measurement with Lidar
Advanced Lidar-Based Wind Field Reconstruction
Parametrization of Wind Turbine Inflow Wind Fields
Wind Field Reconstruction with Nonsynchronous Lidar Data
Uncertainties of Doppler Lidar
Uncertainty on the Line-of-Sight Measurement
Uncertainty on the Reconstructed Wind Speed Measurement
Advantages and Disadvantages of Doppler Lidar
Cross-References
References
23 Load Measurements on Wind Turbines
Contents
Introduction
State of the Art: Technology
Established Measurement Systems
Typical Sensor for Wind Industry
Different Reference Systems and Their Challenges
Measurements of Meteorological Quantities
Tower
Nacelle
Hub
Blades
Synchronization of Subsystems
Data Management
Cross-References
References
24 Surface Pressure Measurements
Contents
Introduction
Pressure Measurement Evolution
Fluid Dynamics of Rotating Blades
Rotational Augmentation
Dynamic Stall
Surface Pressure Taps
Pressure Measurement Tube Dynamics
Rotating Measurement Corrections
Transducers and Data Acquisition
Conclusions
References
Part IV Aerodynamics and Turbulence
25 Introduction to Turbulence
Contents
Introduction
Basic Features of Turbulence
IEC Characterization
Normal Wind Conditions
Extreme Wind Conditions
Idealized Homogeneous Isotropic Turbulence
Correlations
Kolmogorov and Obukhov 1941
Kolmogorov and Obukhov 1962
Multifractal Models
Intermittency
Mathematical Outlook
Discussion
Cross-References
References
26 Turbulent Inflow Models
Contents
Introduction
Recycling Methods
Strong Recycling
Weak Recycling
Synthetic Coherent Eddy and Stochastic Methods
Digital Filter Based Wind Field Generation
Method of Random Spots
Wind Fields Based on Continuous-Time Random Walks
Spectral Methods
The Sandia Method and Rotational Sampling
The Mann Model
Conclusion
Cross-References
References
27 Wind Shear and Wind Veer Effects on Wind Turbines
Contents
Introduction and Definition of Terms
Variability of Shear and Veer
Observations of Wind Shear and Wind Veer
Global Assessments
Site-Specific Observations
Influences of Topography on Shear and Veer
Influence of Wind Shear and Wind Veer on Wind Turbine Power Production
Influence of Wind Shear and Wind Veer on Wind Turbine Wakes
Influence of Wind Shear and Wind Veer on Wind Turbine Loads
Summary and Recommendations
References
28 Turbulence of Wakes
Contents
Introduction
Atmospheric Boundary Layer
Turbulence Wake Structures
Modeling of Turbulence in the Wake
Evolution of Velocity Components in the Wake
Turbulence Intensity
Integral Length Scale
Evolution of the Turbulent Kinetic Energy in the Wake of a Wind Turbine
Energy Spectral Density in the Wake of a Turbine
Further Turbulence Quantities
Multi-scale Properties of Turbulence in the Wake of a Wind Turbine
Intermittency in the Wake of a Turbine
Turbulence in the Wake of a Yawed Turbine
Comparison of Actuator Disk and Wind Turbine Wakes
Conclusion
Cross-References
References
Part V Wind Farm Aerodynamics
29 Wake Structures
Contents
Introduction
Basic Features and Theorems
Wake Structures
Influence of Turbulence
Near Wake Length and Stability
End Note
Cross-References
References
30 Industrial Wake Models
Contents
Introduction
Analytic Wake Models
Top-Hat Models
The Jensen Deficit Model
The Frandsen Deficit Model
The Frandsen (IEC) Turbulence Intensity Model
The Crespo-Hernandez Turbulence Intensity Model
Gaussian Models
The BP Deficit Models
The Ishihara Deficit Model
Double-Gaussian Models
The Double-Gaussian Deficit Model
The Ishihara Turbulence Intensity Model
Equation System Wake Models
CFD Lookup-Table Wake Models
Linearized RANS Models
Eddy-Viscosity Wake Models
Wind Farm Modelling and Wake Interactions
Rotor Equivalent Flow Quantities and Partial Wakes
Wake Superposition
Homogeneous Background Flow
Heterogeneous Background Flow
Superposition of Wake-Added Turbulence Intensity
Wind Farm Calculation Algorithm
Downstream Turbine Evaluation
Iterative Wake Calculation
Cross-References
References
31 Wake Meandering
Contents
Introduction
The Physics Behind Wake Meandering
Wake Meander Modeling: General Considerations
CFD-Based Approach
A Word on CFD and ABL Stability
Concluding Remarks and Outlook
Medium-Fidelity Approach
Quasi-steady Wake Deficit
Wake Meandering Modeling
Wake Self-Generated Turbulence
Wake Superposition: From Single Wakes to Wind Farm Flow Fields
The ABL Stability Aspect
Wake Meander Consequences
Wind Farm Production
Wind Farm Loading
Example DWM Applications
Wind Farm Production Prediction
Wind Farm Load Prediction
The Egmond ann Zee Wind Farm Case
The Lillgrund Wind Farm Case
Optimal Wind Farm Layout
Conclusions and Outlook
Cross-References
References
32 CFD-Type Wake Models
Contents
Introduction
Theory of CFD-Type Wake Modeling
Standard Actuator Disk Model
Actuator Line Model
Advanced Actuator Disk Models
Other Actuator Models
Actuator Surface Model
Actuator Swept-Surface Model
Actuator Sector Model
Actuator Shape Model
Double Multiple Stream Tube
Actuator Block Model
Modeling of Tower and Nacelle
Control Mechanisms
Tip-Loss Correction
Blade-Generated Turbulence
Smearing of the Forces
Conclusion
Verification and Validation
Application of Wake Modeling
Investigation of a Single Wake
Wind Farm Layout Studies
Fully Developed Wind Farm Flow
Impact of Atmospheric Stability
Impact of Terrain
Roughness
Forest
Complex Terrain
Control Strategies
Other Applications
Conclusion
Cross-References
References
33 Wind Farm Cluster Wakes
Contents
Introduction
Measurements of Wind Farm Cluster Wakes
Remote Sensing
In Situ Measurements
Modelling of Wind Farm Cluster Wakes
Global Models
Mesoscale Models
Engineering and Microscale Models
Impact of Cluster Wakes
Impact on Single Flow Situations
Impact on Wind Resources
Impact on Other Meteorological Quantities
Future Needs and Outlook
Conclusions
Cross-References
References
34 Wind Tunnel Testing of Wind Turbines and Farms
Contents
Introduction
Design of Scaled Wind Turbine Models
Scaling Laws
Aerodynamic Scaling, Including Dynamics and Servo-Actuated Models
Aeroelastic Scaling
Gravo-Aeroelastic Scaling
Aerodynamic Design
Airfoil Selection
Blade Shape Design
Aeroelastic Design
Blade Layout
Design of the Composite Structure
Blade Manufacturing
Blade Testing
Hub, Nacelle, and Tower Design
Sub-system Design for a 2m Rotor Model
Sub-system Design for a 1.1m Rotor Model
Sub-system Design for a 0.6m Rotor Model
Actuators and Control
Closed-Loop Control and Data Acquisition
Experimental Setup
Boundary Layer Wind Tunnel
Inflow Conditions
Flow Measurement Devices
Experimental Results
Characterization of a Single Wind Turbine
Testing of Wind Turbine Shutdown Maneuvers
Validation of Wind Observers
Active Load Alleviation
Wake Interaction Experiments
Derating Applied to a Cluster of Three Interacting Wind Turbines
Closed-Loop Wind Farm Control
Closing Remarks
Cross-References
References
35 Wake Measurements with Lidar
Contents
Introduction
Applying Lidar for Measuring Wake Characteristics
Lidar Measurement Principle
Lidar Use Cases
Lidar Configurations for Wake Measurements
Uncertainties and Limitations of Wake Measurements with Lidar
Conclusions
Cross-References
References
36 SAR Observations of Offshore Windfarm Wakes
Contents
Introduction
Basic Principles of SAR Wind Measurements over the Ocean
SAR Basics
Basics of SAR Wind Measurements
Empirical Models for the Microwave Radar Cross Section of the Sea Surface
Inversion Approaches for SAR Wind Speed Retrieval
Past and Existing Satellite SAR Mission and Available Data
Imaging Geometry and Orbits
Existing Satellite SAR Systems
Satellite Products and Radiometric Calibration
Offshore Wind Resource Assessment Using SAR Data
SAR Observations of Wakes Downstream Offshore Windparks
Estimation of Wake Lengths from SAR Data
Wake Length Dependence on Atmospheric Stability
SAR Turbulence Features Related to Horizontal Shear
Increased NRCS Within the Wake Area
Wakes Associated with the Land/Sea Boundary
Artefacts Due to Oceanic Processes
Summary and Outlook
Cross-References
References
37 Met Mast Measurements of Wind Turbine Wakes
Contents
Introduction
What Is the Value of Met Mast Measurements for Aerodynamic Research?
Experiment Layout: Think Before Act
Illustrative Examples
The Rise of LiDAR
How to Obtain the Highest Quality in Met Mast Measurements?
The Value of Standardization
Define Success Criteria
Talk the Same Talk
What Have We Learned from Wind Turbine Wake Measurements?
Flat Terrain, Near Shore
Offshore Wind Farms
Scaled Wind Farm
Conclusion and Outreach
Cross-References
References
38 Aerodynamics of Wake Steering
Contents
Introduction
Wake Steering
Analytical Models for Wake Steering
Jensen and Jimenez Wake Models
Gaussian Model
Wake Steering for Wind Farms
Evaluating the Effects of Counter-Rotating Vortices
One Turbine Case
Two-Turbine Case
Toward Flow Control
Spanwise and Vertical Velocity Components
Added Wake Recovery Due to Yaw Misalignment
Incorporating Secondary Steering Effects by the Introduction of an Effective Yaw Angle
Five-Turbine Analysis
Optimization of Five-Turbine Array
Wind Farm Analysis
A Note on Validation Wake Steering
Conclusions
References
39 Optimizing Wind Farm Layouts
Contents
Nomenclature
Introduction
Overview for the Basic Concepts of Wind Farm Optimization
Guidelines and Standards
Definition for the Optimization Problem
Problem Formulation for Wind Farm Optimization
Wind Farm Modelling
Wind Resource Assessment
Wake Modelling
Power Generation
Economic Modelling
Load Modelling
Modelling for Other Factors
Objective Function
Constraints
Computational Complexity
Methodology for Automated Wind Farm Optimization
Calculus-Based Solutions
Heuristic Optimization Algorithms
Classic Heuristic Algorithms
Metaheuristic Algorithms
Hybrid Approaches
Research Needs and Trends in Wind Farm Optimization
Wind Farm Optimization in Complex Terrain
Optimization for Integrated and Grid-Connect Wind Energy Utilizations
Commercial Software
Cross-References
References
Part VI Alternative Concepts
40 Kites for Wind Energy
Contents
Nomenclature
Introduction
Pumping AWES Components
Pumping AWES Operating Phases
System Design Differences Compared to Conventional Wind Turbines
Airborne Wind Energy Configurations
Soft Wing
Rigid Wing
Theoretical Performance
Idealized Performance Model
Operating Regions
Coordinate Frames
Local-Level Frame
Body Frame
Stability Axis Frame
Aircraft Wind Frame
Ground Wind Frame
Rigid Wing Aerodynamics
High-Lift Airfoils
AP2 Airfoil Characteristics
AP-3 Airfoil Characteristics
Static Wing Aerodynamics
Control Surfaces
CFD Simulations
Unsteady Aerodynamics
Angle of Attack Rate
Sideslip Rate
Roll Rate
Pitch Rate
Yaw Rate
Control Effectors
Methods for Calculating Stability Derivatives
AWES Maneuverability
Summary
Tether Aerodynamics
Introduction
Static Tether Drag
Experimental Flight Dynamics
System Scaling
Commercial-Sized Systems
Aerodynamic Scaling
Aerodynamic Shape Design Methods
Adjoint-Based Optimization Approach
Continuous Adjoint Method Overview
Example Application to AWES
Example Results
Product Roadmap
Conclusions
Cross-References
References
41 Vertical-Axis Wind Turbine Aerodynamics
Contents
Introduction
History of VAWTs
Advantages and Disadvantages Between HAWT and VAWT
Basic VAWT Aerodynamics
Rotor Representations
VAWT Modeling Techniques
1D-Based Streamtube Momentum Models
2D Actuator Cylinder Model
3D Actuator Cylinder Model
Unsteady Aerodynamics
Dynamic Stall
Relevance for VAWTs
Vortex Dynamics During Dynamic Stall
Modeling Dynamic Stall
Flow Curvature
Relevance for VAWTs
Effect of the Pitching Axis
Blade-Vortex Interaction
Wake Aerodynamics
Near and Far Wake
Wake Characteristics
Vortex System
Wake Deflection
Horizontal Wake Deflection
Vertical Wake Deflection
Airfoil Design for a VAWT
Cross-References
References
Part VII Aeroacoustics
42 Wind Turbine Aerodynamic Noise Sources
Contents
Introduction and Scope
Theoretical Works Related to Aerodynamic Noise
Lighthill Acoustic Analogy and Related Works
Noise Edge Scattering
Individual Wind Turbine Noise Mechanisms
Turbulent Inflow Noise
Trailing Edge Noise
Stall Noise
Tip Noise
Blunt Trailing Edge Noise and Laminar Boundary Layer Vortex Shedding Noise
Other Potential Noise Sources
Mechanical Noise
Ground-Borne Noise
Aerodynamics Add-Ons
Noise Mechanisms Specific to Wind Turbines
Rotor Noise
Amplitude Modulation
Low-Frequency Noise
Wind Turbines in Farms
Conclusions
Cross-references
References
43 Wind Turbine Noise Propagation
Contents
Introduction
Factors Affecting Sound Propagation
Geometric Divergence and Atmospheric Absorption
Ground Effects
Refraction by a Moving and Inhomogeneous Atmosphere
Atmospheric Turbulence
Terrain and Barrier Effects
Review of Sound Propagation Models
Engineering Methods
ISO 9613-2
NMPB Method
Nordic and EU Models
Numerical Methods
Linearized Eulerian Equation (LEE)
Particle and Advanced Ray-Tracing Models
Parabolic Equation (PE) Methods
Link with Source Modelling
Including Turbulence Effects
Comparison of Main Methods
Model Accuracy
General Considerations
Measurements and Validation Studies
Variability in Wind Turbine Sound Propagation
Conclusions
Cross-References
References
44 Measuring and Analyzing Wind Turbine Noise
Contents
Introduction
Measuring Noise
Measurement Methods for Development Purposes
Parabolic Microphone
Microphone Array
Downstroke Method
Development of Noise
Conclusions
Cross-References
References
45 Wind Turbine Noise Mitigation
Contents
Introduction
Noise Sources and Characteristics
Noise Reduction Technologies
Turbine Controls
Blade Add-Ons
Blade Geometry
Conclusions
Cross-References
References
46 Direct Prediction of Flow Noise Around Airfoils Using an Adaptive Lattice Boltzmann Method
Contents
Introduction
Methods
Lattice Boltzmann Method
Adaptive Mesh Refinement
Large Eddy Simulation
Boundary Conditions
Aeroacoustic Predictions
Noise Generated by a 2D Cylinder at Re = 150
Direct Noise Calculation of a NACA0012 Airfoil at Re = 500,000
Noise Generated at 0° Angle of Attack
Noise Generated at 10° Angle of Attack
Conclusions
References
Index