Lecture # 14: Wind Turbine Aeromechanics. Dr. Hui Hu. Department of Aerospace Engineering Iowa State University Ames, Iowa 50011, U.S.

Transcription

1 AerE 344 Lecture Notes Lecture # 14: Wind Turbine Aeromechanics Dr. Hui Hu Department of Aerospace Engineering Iowa State University Ames, Iowa 11, U.S.A

2 Wind Energy Production and Wind Turbine Installations in USA Wind farm sites in USA Rest of the world 27.4% electricity of Iowa is from wind Canada 3 France 2 Italy United Kingdom 2 India Spain Germany United States China Installed windpower capacity (GW) 3 Targets of 2% of US electricity from wind energy by 23 and 35% by 2, have been set up by the Department of Energy (DOE) of United States. Iowa is the 3rd in the nation in installed wind energy capacity and it has the highest density of wind power generation capacity with 29.9 kw/km2 According to DoE s wind Technologies Mark Report, Iowa has reached the milestone of 27.4% of the state s electricity in 214, while the national average rate is about 4.9% in 214. Top Wind Energy Production States: Texas: 12,354 MW(8.3%) California: 5,829 MW (6.6%) Iowa: 5,177 MW (27.4%) Illinois: 3,568 MW (4.7%) Oregon: 3,153 MW (12.4%) Oklahoma: 3,134 MW (14.8%) Minnesota: 2,987 MW (15.7%) (214 DoE Wind Technologies Market Report )

3 Wind Resources Map in USA Current wind farms with 8m turbine hub height Wind resources with 14m hub height

4 Technical Challenges Related to Wind Energy Four focus areas identified in 28 DoE Wind Energy Workshop Report: Turbine Dynamics Micro-siting and Array Effects Mesoscale Processes Climate Effects ~2MW wind turbine vs. Boeing 747 airplane Horns Rev offshore wind farm near Denmark A typical Onshore wind farm Schreck S, Lundquist J, and Shaw W (28) U.S. Department of energy workshop report: research needs for wind resource characterization. Technical Report, NREL/TP

5 Aerodynamics and Atmospheric Boundary Layer (AABL) Wind Iowa State University AABL (Aero/ABL) Gust Tunnel Aero Test Section: 8 ft by 6 ft [11 mph] ABL Test Section: 8 ft by 7.25 ft [85 mph] Parameter R (mm) H (mm) d pole (mm) d nacelle (mm) (deg.) a (mm) a1 (mm) A2 (mm) Dimension o :32 scaled model to simulate a 2MW wind turbine with 9m rotor blades ERS- turbine blade design by TPI

6 Y/H Y/H Y/H Experimental Setup to Study Wind Turbine Aeromechanics Power law fit with exponent k.12 Measurement data (a). Mean velocity Power law, = (b). Turbulence intensity Measurement data (c.). Reynolds stress 1..5 Hub height 1..5 Measurement data U/U H u /U H uv /U H Test flow conditions: U hub = 6 m/s, Re c = 1, Tip speed ratio: λ = ~ 6.5. Measured parameters: Characteristics of turbine wake flows Power output of wind turbine models Dynamic wind loads acting on wind turbines Experimental Setup JR3 load cell

7 Near Wake Measurement Results at Tip-Speed Ratio, =3. Spanwise Vorticity 1/s m/s Shadow =3. = X (mm) Shadow Time-averaged velocity distribution Turbulence intesity r.m.s.(u) / U 2 2 Phase-Locked PIV measurement results Nomalized Turbulence Kinetic Energy Turbulence intesity r.m.s.(v) / U X (mm) X (mm) Instantaneous PIV results = 3. 4 m/s Shadow - Phase angle=deg Y (mm) Mainstream Velocity m/s Y (mm) Y (mm) Wind Speed (m/s) Shadow Y (mm) Y (mm) =3. Shadow Y (mm) = X (mm) Turbulence intensity r.m.s (u)/uo 2 = Shadow X (mm) Turbulence intensity r.m.s. (v)/uo - 2 X (mm) Normalized Turbulence (u ' u ' v' v' ) kinetic energy 2U o 2 2

8 Phase-Locked PIV Measurement Results at Tip-Speed Ratio, =3. Wake vortex structures at different phase angles Reconstructed 3-D wake vortex structures 1..8 Decay of tip vortex strength.6 z (x)/.4 y = a*x b ; a=.323, b=-.197 Measurement data (Hu et al. Experiments in Fluids, 212, DOI: 1.7/s ) X/R

9 Y (mm) Y (mm) Y (mm) Y (mm) Effects of Tip-speed Ratio on the Wake Vortex Structures Spanwise Vorticity 1/s = 3. Phase angle=deg Spanwise Vorticity 1/s = 3.5 Phase angle=deg Shadow a). = X (mm) Shadow - b). = X (mm) Spanwise Vorticity 1/s = 4. Spanwise Vorticity 1/s = 4.5 Phase angle=deg Phase angle=deg Shadow - c). = X (mm) Shadow - d). = X (mm)

10 Y (mm) Y/D Y (mm) Y/D Wake Profiles at X/D=.5 Downstream of the Wind Turbine Model Wind Speed (m/s) 4. m/s Shadow =3. Wind Energy 1 2 A V 3 Aerodynami c Tip height Force X/D=.5 Probe data(oncoming flow) Curve fit =4.5 =4. =3.5 =3. Hub height 1 2 A V X (mm) Nomalized Turbulence Kinetic Energy X/D=.5 U/U Tip height Shadow = Hub height =4.5 =4. =3.5 = X (mm) (Hu et al., Experiments in Fluids, Vol. 52, No. 5, pp , 212) Turbulent Kinetic Energy

11 Wind Turbine Failures Caithness Wind Farm, UK (22 WT in operation in construction) Total number of accidents: 145 Human fatalities & injuries: Blade failure: 265 Fire: 22 Structural failure: 138 Ice throw: 34 Transport: 113 Environmental (bird death): 128 Others: 282

12 Dynamic Wind Loads Acting on Wind Turbines 3 1. Gaussian distribution function Measurement data Measurement data Time-averaged thrust coefficient Number of the samples Thrust coefficient, CT.8 3 Y X Z CT Time, (s) JR3 Force/Moment Transducer (a). Measured thrust coefficient data Gaussian distribution function Measurement data Time-averaged bending moment coefficient fo=17hz A. U. Number of the samples Bending moment coefficient, CMz Measurement data fo 4 3fo Time, (s) CMz (b). Measured bending moment data (Hu et al., Experiments in Fluids, Vol. 52, No. 5, pp , 212) Frequency (Hz) 8 1

13 Wind Loads Acting on Various Components of Wind Turbine Time-averaged loads: Dean thrust coefficients Fatigue loads: Dynamic thrust coefficients tower Tower + nacelle Non-rotating turbine Rotating turbine Time-averaged loads: Mean bending moment Fatigue loads: Dynamic bending moment Test conditions: Oncoiming ABL wind Velocity at hub height U Hub = 4.8 m/s Chord Reynolds number, Re 7,2 Tip-speed-ratio, = 4.6

14 Wind Farm Aerodynamics: Wake Interferences of Multiple Wind Turbines Offshore wind farms: Wind turbine sitting on flat ocean surface. High wind speed with relatively low ambient turbulence. Near neutral atmospheric boundary layer winds. Onshore wind farms: Atmospheric stability is rarely close to near-neutral, varying significantly between highly convective daytime conditions and highly stable nocturnal conditions. Much higher turbulence level. Wind turbine sitting over complex terrains. Most of the existing wind farm design criterion and standards are derived based on the researches of offshore wind farms. They may not be applicable for onshore wind farms. Horns Rev offshore wind farm near Denmark Onshore wind farm

15 z/h Z/H z/h Z/H Atmospheric Boundary Layer Winds: Offshore vs. Onshore Wind Farms Terrain Category Terrain description 1 Open sea, ice, tundra desert 2 Open country with low scrub or scattered trees 3 Suburban area, small towns, wooded areas Gradien t height, Z G (m) Roughness length, Z O (m) Wind Speed exponent, U( z) U Z G Power law ( =.11) Experimental data Offshore wind farm =.11 Z Z G Tall buildings, city centers, developed industrial areas Power law ( =.15) Experimental data Onshore wind farm = U(z)/U hub Turbulence intesity (%) Low turbulence intensity case (1% at hub height) U(z)/U hub Turbulence intesity (%) High turbulence intensity case (18% at hub height)

16 The Effects of ABL Turbulence Level on the Wake Vortex Dissipation Low turbulence Measured at x/d=1. downstream High turbulence Measured at x/d=1. downstream The evolution of the tip vortex structures in the wake of wind turbine model

17 The Effects of ABL Turbulence Level on the Wake Characteristics Atmospheric boundary layer wind X/D D Wake velocity profiles for low turbulence inflow case Wake velocity profiles for high turbulence inflow case

18 The Effects of ABL Turbulence Level on the Wake Characteristics Atmospheric boundary layer wind X/D D a small generator inside the nacelle Varying R V Wake velocity deficit profiles for low turbulence inflow case Wake velocity deficit profiles for high turbulence inflow case Power output of the downstream wind turbine vs. X/D

19 The Effects of Oncoming Turbulence Level on the Wake Characteristics Atmospheric boundary layer wind X/D D The mean thrust coefficient, C T Z Y X Force/Moment Transducer Standard deviation of the thrust coefficient, C T vs. X/D Turbulence shear stress in the wakes

20 Wake Interferences among Multiple Wind Turbines 3D 3D 3D 3D D Field measurement data (Barthelmie et al., 27) deep array effect deep array effect Velocity profiles in the wake for low turbulence inflow case Velocity profiles in the wake for high turbulence inflow case Power outputs of the wind turbines in a line

21 Effects of Terrain Topology on the Performances of Wind Turbines Quantifying the flow characteristics of surface winds (both mean and turbulence characteristics) over a flat surface (baseline case) and complex terrains for the optimal site design of turbines. Wind flow Wind turbine array Z Y X Characterizing the turbulent wake flows and dynamic wind loads (both forces and moments) as well as their relationships for single wind turbine sited over a flat surface (baseline case) and complex terrains for the optimal mechanical design of wind turbines. Hill#1 Hill#2 Wind turbines over complex terrains Investigating the effects of array spacing and layout on the wake interferences among multiple wind turbines sited over a flat surface (baseline case) and complex terrains for higher total power yield and better durability of wind turbines.

22 Effects of Complex Terrains on the Wind Turbine Performance Low slope hill L=2h Slope =12 Gaussian curve: 2 x z h exp.5, L D ridge with Gaussian shape h/2 h 3D 3D 3D 3D High slope hill L=h h/2 Slope =22 L 2-D ridge with Gaussian shape h 3D 3D 3D 3D L Flat surface D 3D 3D 3D 3D pos1 pos2 pos3 pos4 pos5

23 Performances of Single Wind Turbine Sited over Complex Terrains 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D pos1 pos2 pos3 pos4 pos5 Wind turbine position pos1 pos2 pos3 pos4 pos5 Power output low slope hill (normalized with power output of single wind turbine sited on flat surface ) Power output high slope hill (normalized with power output of single wind turbine sited on flat surface )

24 Power Outputs of Wind Turbines over Flat Surface vs. Complex Terrains 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D pos1 pos2 pos3 pos4 pos5 Wind turbine position pos1 pos2 pos3 pos4 pos5 Total Power output flat surface (normalized with power output of single wind turbine sited on flat surface ) Power output low slope hill (normalized with power output of single wind turbine sited on flat surface ) Power output high slope hill (normalized with power output of single wind turbine sited on flat surface ) (~26% more) (~24% less)

25 Performances of Wind Turbines over Complex Terrains Moderate slope 2D-Ridges 6D 6D 6D 6D Wind turbine position pos1 pos2 pos3 pos4 pos5 Power output wind turbines (normalized with power output of single wind turbine sited on flat surface ) Wind turbine position pos1 pos2 pos3 pos4 pos5 Two hills Thrust Coefficient C T Bending moment Coefficient C MZ (Tian et al, Renewable Ennergy, 213)

26 Root Loss and Wake Loss of Wind Turbines Root Loss (~5%): Inner 25% of rotor blades are designed to provide structural integrity. The aerodynamically poor design at the root region would result in a dead wind zone where virtually no energy is extracted from the incoming wind. Wake Loss ( up to 4%): Aerodynamic interaction between wind turbines will results in significant energy loss ( up to 4%). Wake loss is due to the ingestion of low-momentum air in wakes from upstream turbines by the downstream turbines. Hu et al. (214) DRWT concept Horns Rev offshore wind farm near Denmark ABL wind Entrainment of high-speed airflow from above to recharge the wake flow SRWT DRWT X/D D

27 Dual-Rotor Wind Turbine Models and Counter-Rotating Rotor Concept Soviet Ka-2 helicopter with counterrotating rotors Contra-rotating propeller SRWT Co-rotating DRWT Counter-rotating DRWT

28 SRWT vs. Co-Rotating DRWT vs. Counter-rotating DRWT Phase-locked PIV measurement results SRWT Co-rotating DRWT Counter-rotating DRWT

29 Ensemble-averaged PIV measurements Velocity distributions X/D.7 PIV window # X/D PIV window # PIV window # PIV window # PIV window # Y/D Normalized Velocity: U/Uhub Normalized Velocity: U/Uhub CN-DRWT Y/D Normalized Velocity: U/Uhub Y/D 1. CO-DRWT X/D PIV window #2.7 SRWT

30 Streamwise flow quantities in the wake X/D=2. X/D=4. X/D=6. X/D=8. X/D=2. X/D=4. X/D=6. X/D=8. 39

31 Stereo-PIV measurement Results: SRWT and DRWTs SRWT CO-DRWT CN- DRWT

32 Stereo-PIV measurement Results: SRWT and DRWTs SRWT CO-DRWT CN-DRWT SRWT CO-DRWT CN-DRWT

33 SRWT vs. Co-rotating DRWT vs. Counter-rotating DRWT ABL wind Entrainment of high-speed airflow from above to recharge the turbine wake flow X/D Power measurement for the same downstream wind turbine a small generator inside the nacelle Varying R ~ 8% more energy output for CN-DRWT. Power/Power SRWTO CN-DRWT CO-DRWT SRWT ~ 1% more energy output form the same turbine at X/D=4. when it is installed in the wake of CN-DWRT X/D V

34 Dynamic wind loads for SRWT and DRWTs SRWT CO-DRWT CN-DRWT

35 Comparison of SRWT and DRWT: Thrust Force and Bending Moment Time-averaged wind loads acting on the wind turbines: SRWT Configurations Thrust loading (C Fx ) Camera 1 Camera 2 Bending Moment (C My ) SRWT Co-rotating DRWT Counter-rotating DRWT ~1% more mean wind loads for DRWTs Co-rotating DRWT Fluctuations of the dynamic wind loads acting on the wind turbines: Configurations σc Fx σc My SRWT Co-rotating DRWT Counter-rotating DRWT Counter-rotating DRWT %~3% higher wind load fluctuations for DRWTs

36 Thank you Very Much for Your Time! Questions?