View
234
Download
2
Category
Preview:
Citation preview
Department of Mechanical EngineeringTechnical University of Denmark
The Aerodynamics of Wind Turbinesby
Jens Nrkr Srensen
Department of Mechanical Engineering (MEK)Center for Fluid Dynamics
Technical University of Denmark
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyBrief history: The first power producing wind turbines were developed in the 1890s
The Suez crisis (1957) renewed the interest in wind energy
The energy crisis in 1973 forced a world wide interest into wind energy
National MW machines were erected in in 1980s and the first commercial MW machinewas designed in 1990
State of the art wind turbines have rotor diameters of 120 m and 5 MW installed power
Department of Mechanical EngineeringTechnical University of Denmark
Wind Energy
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyVarious wind turbines :
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyThe Danish Concept:
3-bladed upwind machine with gearbox and asynchroneous generator
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyThe worlds largest wind turbineEnercon 126: P=6MW; D=126m
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyDevelopment in wind turbine technology :
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergySome (crude) Rules of Thumb:
P: Installed Power (kW) R: Radius (m)T: Time for one turn (s)
R = 10*TP = 1.2*R**2
][]1[2]/[ mRssmtipV =
TtipVR = 2/or
]/70,/60[ smsmtipV where
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergySome characteristics numbers:
Boing 747 (Jumbo jet) wing span: 68 mDiameter of modern wind turbine : 124 m
Area of soccer field: 7.000 m**2Area of rotor plane : 12.000 m**2
Question:How much air is passing through a rotor plane at a wind speed of 10m/s? Answer:Q = rho*A*V = 1.2*12.000*10 = 144 ton per second
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyWind turbine nacelle :
Rotorblade
Hub Tower
Shaft Gear
Disc Brake
Generator
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyAerodynamic forces :
Department of Mechanical EngineeringTechnical University of Denmark
Rotor AerodynamicsAerodynamic forces and geometry :
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyPressure and Forces on Airfoil :
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyBlade-Element MomentumTheory:
Rotor divided into independent stream tubes
Forces determined from airfoil data
Induced velocities computed from general momentum theory
Finite number of blades introducedby Prandtl tip correction
Ad-hoc corrections for off-design conditions, such as dynamic effects,and yaw misalignment
Department of Mechanical EngineeringTechnical University of Denmark
Blade Element Momentum Model
Basic ingredients of the BEM model:
Based on 1-D momentum theory assuming annular independency
Loading computed using tabulated static airfoil data
Dynamic stall handled through dynamic stall models
3-dimensional stall introduced through modifications
Tip Flows based on (Prandtl) tip correction
Yaw treated through simple modifications
Heavily loaded rotors treated through Glauerts approximation
Wakes and park effects modelled using axisymmetric momentum theory
Department of Mechanical EngineeringTechnical University of Denmark
The Optimum Rotor
What is the optimum number of blades ?
What is the optimum operating condition (TSR)?
What is the maximum efficiency?
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Rotor AerodynamicsWhat is the optimum number of blades?
3 blades ?
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Rotor AerodynamicsWhat is the optimum number of blades?
3 blades ?
many blades ?
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Rotor AerodynamicsWhat is the optimum number of blades?
3 blades ?
many blades ?
2 blades ?
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Rotor AerodynamicsWhat is the optimum number of blades?
3 blades ?
many blades ?
2 blades ?
1 blade ?
Department of Mechanical EngineeringTechnical University of Denmark
Why 3 blades?
Aerodynamics: Close to optimum
Struktural-dynamics: Symmetric moment of inertia
Loadings: Forces smeared out on three blades
Estetics: Harmonic rotation
Historics: The concept is well-proven
Department of Mechanical EngineeringTechnical University of Denmark
Optimum rotor with infinite number of blades1-D Axial momentum theory:
oVva /1=
)(2 voVvoAT =
2)1(4 aaPC =593.027
16max ==PC
:31=a
Betz limit:)1(4 aaTC =
oV
)1( aoV
)21( aoV
)(22 voVvoAP = = VmT
= vTP
Axial interference factor:
Thrust Coefficient:
3 oVoAP
PC =Power coefficient:
2 oVoAT
TC =
Department of Mechanical EngineeringTechnical University of Denmark
Optimum rotor with infinite number of bladesGenerel momentum theory:
Vova /1=
rooua =
( ) = 103128 odxoxaaoPC
)14/()31( = aaa
Condition for optimum operation:
Eulers turbine equation:
0.5 0.2881.0 0.4161.5 0.4802.0 0.5122.5 0.5325.0 0.5707.5 0.58210.0 0.593
maxPCTSR
Department of Mechanical EngineeringTechnical University of Denmark
Two definitions of the ideal rotor
Joukowsky(1912)
Betz(1919)
blade span
(r)
R 0
V w const =const =V w
In both cases only conceptual ideas were outlined for rotors with finite number of blades,whereas later theoretical works mainly were devoted to rotors with infinite blades!
blade span
R0
Department of Mechanical EngineeringTechnical University of Denmark
Betz condition for maximum efficiencyof a rotor with a finite number of blades
Maximum efficiency is obtained when the pitch of the trailing vortices is constant and each trailing vortex sheet translates backward as an undeformed regular helicoidal surface
Department of Mechanical EngineeringTechnical University of Denmark
Induced velocities:Movement of vortex sheet with constant pitch and constant velocity
w2z coswu =
sincoswu =
Axial induced velocity:
Tangential induced velocity:
rwVrddz == /)(tan
== BwVBrh /)(2/tan2
Pitch:
Department of Mechanical EngineeringTechnical University of Denmark
Optimum lift distribution:
)(2//)()( wVwBhwrrG == Goldstein function:
Kutta-Joukowski theorem:o
o U2
LcCULcC ==
Combining these equations, we get
)/()/()1(2
VURrGww
LC
o
=
Solidity: oR2
Bc
= Tip Speed ratio: VR
=
Department of Mechanical EngineeringTechnical University of Denmark
The optimum rotor:
Department of Mechanical EngineeringTechnical University of Denmark
Comparison of maximum power coefficients
( )1
10
2= I G x xdx
( )1 3
3 2 20
2=+
x dxI G xx l
=wwV
Mass coefficient
Axial loss factor
1 32 1 2 2Pw wC w I I =
1 2 32 1 2 2P
a aC a J J J =
Solution of Betz rotor (Okulov&Srensen, 2008)
Solution of Joukowsky rotor (Okulov & Srensen, 2010)
Difference between power coefficients
2 2 21 2 3 1 2 1 2 3 3
1 33J J J J J J J J J
aJ J
+ +=
( )2 21 3 1 1 3 33
2
3
+ +=
I I I I I Iw
I
zuaV
=
( )13
0
2 zu x
J l xdxa
=
2
1 21 2lJR
= +2
2 2
1 112 6
JR R
= + +
Department of Mechanical EngineeringTechnical University of Denmark
Optimum 3-bladed rotor with loss:
From C. Bak: J. Physics: Conference Series, vol. 75, 2007
Department of Mechanical EngineeringTechnical University of Denmark
Wind EnergyPerformance of wind turbines :
Department of Mechanical EngineeringTechnical University of Denmark
Control and regulation of wind turbines
Stall control
Active Stall control
Pitch control
Variable speed
Department of Mechanical EngineeringTechnical University of Denmark
Rotor AerodynamicsAerodynamic forces and geometry :
Department of Mechanical EngineeringTechnical University of Denmark
Stall-regulated wind turbine:Computed power curve
Department of Mechanical EngineeringTechnical University of Denmark
Wind TurbineModern Danish Wind Turbine : Pitch-regulated P=2 MW; D=90 m Nom. Tip speed.: 70 m/s Rotor: 38t, Nacelle: 68t; Tower: 150t Control: OptiSpeed; OptiTip
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Rotor Aerodynamics
Basic features:
Rotor blades are always subject to separated flows
Blade aereodynamics dominated by strong rotational effects
The incoming wind is always unsteady and 3-dimensional
Wind turbines are designed to run continuously in about 20 years in all kinds of weather
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine AerodynamicsImportant areas of research:
Aerofoil and blade design
Dynamic stall
3-dimensional stall
Tip Flows and yaw
Modelling of heavily loaded rotors
Wakes and park effects
Complex terrain and meteorology
Offshore wind energy
Department of Mechanical EngineeringTechnical University of Denmark
Research in Wind Turbine AerodynamicsNeed for models capable of coping with: Dynamic simulations of large deformed rotors
Complex geometries: Rotor tower interaction
Adjustable trailing edge flaps
Various aerodynamic accessories, such as vortex generators, blowing, Gourney flaps and roughness tape
3-dimensional stall, including laminar-turbulent transition
Unsteady, three-dimensional and turbulent inflow
Interaction between rotors and terrain
Complex terrain and wind power meteorology
Offshore wind energy: Combined wind and wave loadings
Department of Mechanical EngineeringTechnical University of Denmark
Wind Turbine Aerodynamics
Available models:
Blade-Element momentum (BEM) technique
Vortex line / Vortex lattice modelling
Actuator disc / Actuator line technique
Computational Fluid Dynamics (CFD)
Remark: All models have their individual advantages and disadvantages!
Department of Mechanical EngineeringTechnical University of Denmark
Computational Fluid DynamicsBasic Elements
Mesh generation
Turbulence modelling
Efficient computing algorithms
High-performance computers
Post-processing facilities (Validation)
Department of Mechanical EngineeringTechnical University of Denmark
The Numerical Wind Tunnel (EllipSys)
Developed in close collaboration between DTU and Ris with the aim of:
Optimizing rotors with respect to performance and noise
Analysing existing designs
Verification of simple engineering models
Gain physical understanding
Department of Mechanical EngineeringTechnical University of Denmark
Pressure Distributions at 10 m/s(Courtesy: Niels N. Srensen, Ris)
Department of Mechanical EngineeringTechnical University of Denmark
Actuating trailing edge flapAn example of a research project
Department of Mechanical EngineeringTechnical University of Denmark
Actuating trailing edge flapIn this project we investigate the possibility of using flapping trailing edge flaps to control and reduce the impact of small-scale turbulence on the loading of a wind turbine rotor
Department of Mechanical EngineeringTechnical University of Denmark
3D rotor code using Immersed Boundaries
EllipSys3D are being extended to include a trailingedge flap by using immersed boundary technique
The influence of upstream perturbations are beinginvestigated by imposing upstream vortexsources
The model has recently been extended toinclude wind tunnel walls
Upstream turbulence will be included and morevalidation will take place in the next phase
Department of Mechanical EngineeringTechnical University of Denmark
ATEF combined with curvilinear mesh
Department of Mechanical EngineeringTechnical University of Denmark
ATEF combined with curvilinear mesh
Department of Mechanical EngineeringTechnical University of Denmark
Wind tunnel measurements at DTU
A new airfoil with a trailing edge flap has beeninstalled in the 50cm x 50 cm wind tunnel atDTU Mechanical Engineering
A set-up controlling two small oscillating airfoils have been designed to create upstream disturbances
The airfoil and the wind tunnel has both beenequipped with pressure transducers (in total 64)
The set-up is operating with a controllable TEFand a LabView program to determine loadings,i.e. unsteady lift and drag coefficients
The new measurement campaign has been initiated
Department of Mechanical EngineeringTechnical University of Denmark
Status of wind tunnel measurements
The old blade mounted on a balance measuring one force component
NACA 63418 wing: 25cm chord 50cm span Mechanical hinged flap, 15% flap RC-model actuator
Department of Mechanical EngineeringTechnical University of Denmark 50
Suggestion for new flap mechanism
Flexiure
LinMot
Mechanism
Department of Mechanical EngineeringTechnical University of Denmark 51
New airfoil with new flap mechanism
Department of Mechanical EngineeringTechnical University of Denmark 52
Red wind tunnel testRed Wind Tunnel:
50cm x 50cm Max speed: 65m/s, Tu
Department of Mechanical EngineeringTechnical University of Denmark 53
Wind tunnel testing NACA 63418 / 64418Experimental setup :
Pressure scanner 2x32 tabs implemented, LabView measuring chain operational
Measurement of pressures on wing and tunnel walls
Sampling rate:150-200Hz (Integral loads and control)
Aerodynamic excitation - High frequency (10-20Hz) pitchable wings upstream of test wing
LinMot
Mechanism
Department of Mechanical EngineeringTechnical University of Denmark 54
Wind tunnel test, NACA 63418/64418
0 00 55 5
f [Hz]0 5 1/2/5/85 5 1/2/5/8
f [Hz]0 8 1/2/5/85 8 1/2/5/8
Steady flap and airfoils
Unsteady flap and steady airfoils
Steady flap and osc. airfoils
U = 30 m/s
Tu 0.1%
- main wing AOA
- flap angle
- 2 airfoils angle
Department of Mechanical EngineeringTechnical University of Denmark 55
Oscillating wingsTunnel:
V = 30 m/s
Oscillating wings (NACA 64015) c = 0.1m f = 5 Hz = 8o
Main wing: NACA 63418 c = 0.2ma= 0oflap = 0o fflap = 0 Hz
Department of Mechanical EngineeringTechnical University of Denmark 56
Flap (15%) 8HzTunnel:
V = 30 m/s
Oscillating wings (NACA 64015) c = 0.1m f = 0 Hz = 8o
Main wing: NACA 63418 c = 0.2ma= 5oflap = 5o fflap = 8 Hz
Department of Mechanical EngineeringTechnical University of Denmark 57
Results moving flap
Reynolds Averaged Navier-Stokes Angle of attack: = 0 Reynolds number: Re = 1.000.000
flapping angle : -9 < < +9
Frequency: f = 0.05/s
Department of Mechanical EngineeringTechnical University of Denmark
Combined pitch and flap motion
Department of Mechanical EngineeringTechnical University of Denmark
The Aerodynamics of Wind Power
Conclusion:
In spite of the many years humans have expolited the energy of the wind, there is still a big need for improving our basic knowledgeof wind turbine aerodynamics
Slide Number 1Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40Slide Number 41Pressure Distributions at 10 m/s(Courtesy: Niels N. Srensen, Ris)Slide Number 43Slide Number 443D rotor code using Immersed Boundaries Slide Number 46Slide Number 47Wind tunnel measurements at DTU Status of wind tunnel measurements Suggestion for new flap mechanismNew airfoil with new flap mechanismRed wind tunnel testWind tunnel testing NACA 63418 / 64418Wind tunnel test, NACA 63418/64418 Oscillating wingsFlap (15%) 8HzResults moving flap Combined pitch and flap motion Slide Number 59
Recommended