Wind Energy

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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

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

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.

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

12 ρV∞

2 ⋅ c

12 ρV∞

2 ⋅ c

Lift-to-Drag Ratio:

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

~15o 0o

max CL

Lift Curve   Lift and drag of an airfoil

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

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: English Wikipedia

Power Coefficient   Power coefficient a measure on how much power a wind

turbine can extract from the wind.

12 ρU

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

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

Tower   Tower needs to withstand large loads

Source: Danish Wind Association Source: Nordex

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

Coastal Breezes

Mountainous Terrain

Ridge Effects

Mountainous Terrain

Wind Rose   Analysis of a possible wind turbine location   Install data acquisition equipment and measure for

extended period of time wind speed and direction.

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: Gipe, 2009

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)

Wind Farms   Wake of upstream turbines disturbs downstream ones,

Wind Farms   Reduced power compared to free-standing wind turbines

Wind Power with Kites?   Can kites be used for wind generation?   Kite-Gen concept:

  Thanks

Wind Energy

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