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Wind Energy
Asst. Prof. Jörg SCHLÜTER
Introduction to Energy
Picture: Vestas
About me: Asst Prof. Jörg SCHLÜTER
(pronounce: York SHLOOTER) School of Mechanical and Aerospace Engineering Aerospace Division Teaching and researching in Aerodynamics Master’s from TU Berlin, Germany PhD from ENSEEIHT (N7), Toulouse, France Worked for 5 years at Center for Turbulence
Research at Stanford University, USA At NTU since 2005 In charge of the Aerodynamics Group at the
Aerospace Division
Outline Wind Power Basics Horizontal and Vertical Axis Wind Turbines Basic Aerodynamics Components of Wind Turbines Wind Turbine Siting
Wind Energy Explained, 2nd ed. Manwell, McGowan, Rogers Wiley, 2010
Wind Energy Basics, 2nd ed. Paul Gipe Chelsea Green Publishing, 2009
Wind Power Basics Dan Chiras New Society Publishers, 2010
Wind Power History Wind Power around for many years Used for mechanical work: grinding, pumping etc.
Wind Energy Wind turbines to produce electricity Fast growing market
Source: Chiras, 2010
Size and Power of Wind Turbines Current sizes and power of wind turbines
Source: Gipe, 2009
Size and Power of Wind Turbines Wind Turbine Size Classes
Source: Gipe, 2009
Size and Power of Wind Turbines
Source: Manwell, 2010
Types of Wind Turbines Vertical Axis Wind Turbines (VAWT) Horizontal Axis Wind Turbines (HAWT)
Vertical Axis Wind Turbines (VAWT) Drag-based and lift-based VAWT
Source: Manwell, 2010
VAWT at NTU Cygnuspower VAWT
VAWT Development at NTU Design and analysis of a VAWT
Simulation:
Wind Tunnel Experiment:
Horizontal Axis Wind Turbines (HAWT) All HAWT are lift-based
Source: Manwell, 2010
Power Curve of a Wind Turbine
Cut-in wind speed: Wind speed at which the blades start spinning (dependent on aerodynamic design, generator and mechanical design)
Cut-out wind speed: Maximum wind speed that the wind turbine can sustain.
Source: Manwell, 2010
Aerodynamic of a Turbine Blade Aerodynamic performance of a wind turbine Wind turbine blade consists of a series of airfoils.
Airfoil Terminology
source: Anderson, Intro. To Flight
Lift and Angle of Attack Lift and drag coefficient
source: Anderson, Intro. To Flight
L
D
€
CL =L
12 ρV∞
2 ⋅ c
€
CD =D
12 ρV∞
2 ⋅ c
Lift-to-Drag Ratio:
€
e =LD
=CL
CD
ρ: density
Lift at an Airfoil
2/3 of lift on upper surface
1/3 of lift on lower surface Source:http://hyperphysics.phy-astr.gsu.edu
Lift Curve
angle of attack α
CL
~15o 0o
max CL
Lift Curve Lift and drag of an airfoil
Source: Manwell, 2010
Aerodynamic Design of a Blade How to design an turbine blade: Choose airfoil shapes along the turbine blade such that
each has the best lift-to-drag ratio Different speeds of tip and hub require different shapes
and different angles of attack (twist) along the blade
Aerodynamic Design of a Blade Example
Source: Manwell, 2010
Tapering of a Wind Turbine Blade To account for the slower movement of the blade close to
the hub, a larger chord length can be chosen tapering
Source: Manwell, 2010
Source: English Wikipedia
Source: Manwell, 2010
Power Coefficient Power coefficient a measure on how much power a wind
turbine can extract from the wind.
€
CP =P
12 ρU
3A=
Rotor PowerPower in the wind
ρ: density; U: wind speed; A: area swept over by the blades
Aerodynamic Efficiency of a Wind Turbine The aerodynamic efficiency of a wind turbine is limited by
the Betz-Limit
Source: Manwell, 2010
Wake Rotation Spinning blades introduce rotational movement to the flow Loss of energy
Wind Turbine Nacelle Nacelle of HAWT contains gear box, generator, yaw drive
and pitch control.
Gear Box Required to translate low turbine rpm to higher rpm
suitable for efficient generator operation
Source: Nordex
Gear Box Failure Gear box introduces transmission inefficiency and
potential failure
Source: SPON
Direct Drive Direct drive generators eliminate gear box
Source: MTorres
Yaw Drive Yaw drive moves actively the wind turbine into the wind
Source: Manwell, 2010
Tower Tower needs to withstand large loads
Source: Danish Wind Association Source: Nordex
Source: Krohn, DWIA
Source: Krohn, DWIA
Tubular Steel Towers Lattice Towers Guyed Pole Towers
Source: Greenward Technology
Buckling:
Wind Turbine Installation Challenges of Wind Turbine Installation Shipping of large blades Installation of blades during wind
Source: Vestas
Wind Turbine Siting Where to install a wind turbine? Location! Location! Location!
Global positioning Local positioning Height and effects of obstacles Wind farms
Global Positioning
Source: Chiras, 2010
Coastal Breezes
Source: Chiras, 2010
Mountainous Terrain
Source: Chiras, 2010
Ridge Effects
Source: Manwell, 2010
Mountainous Terrain
Source: Manwell, 2010
Mountainous Terrain
Source: Chiras, 2010
Wind Rose Analysis of a possible wind turbine location Install data acquisition equipment and measure for
extended period of time wind speed and direction.
Source: Manwell, 2010
Installation Height Atmospheric Boundary Layer
viscous forces slow down the flow at the surface
“no slip” condition!
velocity vectors
Installation Height Atmospheric Boundary Layer Increase of wind speed with height:
Source: Gipe, 2009
Installation Height Atmospheric Boundary Layer Increase of wind power with height:
Source: Gipe, 2009
Obstacles in the Flow
Source: Chiras, 2010
Obstacles in the Flow
Source: Chiras, 2010
Obstacles in the Flow
Source: Gipe, 2009
Obstacles in the Flow
Source: Manwell, 2010
Offshore Use of wind turbines off-
shore Advantages: Higher wind speeds Lots of space
Disadvantages: Higher installation and
maintenance cost (~ x3) Far away from power grid Not much long-term
experience
Source: REPower
Offshore Installation Note: Taller structures, higher loads compared to oil rigs
Source: NREL
Wind Farms For efficiency purposes wind turbines can be clustered Facilitates connection to the grid (esp. offshore)
Source: Manwell, 2010
Wind Farms Wake of upstream turbines disturbs downstream ones,
Wind Farms Reduced power compared to free-standing wind turbines
Source: Manwell, 2010
Wind Power with Kites? Can kites be used for wind generation? Kite-Gen concept:
Thanks