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Wind Power and WindTurbinesBJ Furman
K Youssefi13FEB2008
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Outline
Wind causes?
Wind Power example
Wind Turbine Design
Aerodynamics
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Windwhat causes it?Atmospheric
pressure differences Where does the
pressure come
from?
Weight of air inatmosphere
Area
ForcePressure
~31 km(99% of mass)
Avg. pressure at sea level
101325 Pa (Pascal)
1013.25 mb (millibar)
29.92 in. Hg (inches of mercury
1 atm (atmosphere)
14.7 psi (pound per square inch)
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Pressure
depthgDensityPressure Area
ForcePressure (Definition)
Earths surface
depthgravitytodueonacceleratiPressure volumemass
ms
mPressure 23
mkg
Check the formula by checking the units!
Units multiply and divide like numbers!
Space (zero pressure)
Edge of atmosphere
22
2
22s
mkg
ms
1Pressurem
N
mmkg
Okay!
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Windwhat causes it?, cont. Pressure differences cause the flow off lu ids(gasesand liquids)
pressure is always measured relative to somereferencepressure Sometimes relative to vacuum absolute Sometimes relative to atmospheric pressure
hPB PA
The higher pressure at B will cause fluid to flow out of the tank.
So, what causes pressure variations in the atmosphere?
AB PhgP
Fluid density
Acceleration due to gravity
Fluid height
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Prevailing Winds Heating and cooling of the air
https://reader009.{domain}/reader009/html5/0404/5ac3d01cbfd0d/5ac3d020c
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Windwhat causes it?, cont.Pressure maps
Contours of
constant pressure
(usually 4 mb
between contours
Close spacingmeans stronger
winds
In N.H., winds
circulate around a
low pressure region
in CCW direction
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Weather Processor SymbolsWXP Legend
http://virga.sfsu.edu/inline/legend.gif
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Review Question 1
What causes wind?
A. Air pressure
B. Weight of the atmosphere
C. Pressure difference inatmosphere
D. Low pressure
E. High pressure
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Review Question 2
What are the units of pressure?
A. Force/Area
B. Pascals (Pa)
C. Pounds per square inch (psi)
D. Millirads
E. B and C
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Wind Energy and Power Atmospheric pressure differences
accelerate and impart kinetic energy intothe air
Wind energy conversion machines (WEC)convert wind energy into electrical or
mechanical forms How much powercan we extract?
time
)()(
time
K.E.Power
22
1 velocitymass
velocityareadensitytimemass
2)()(Power
33
21
AVvelocityareadensity
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Wind Power - Example
Example:
V = 10 m/s
A = (2 m)2 = 4 m2
= 1.2 kg/m3
http://z.about.com/d/gonewengland/1/0/5/C/leaf5.gif
https://reader009.{domain}/reader009/html5/0404/5ac3d01cbfd0d/5ac3d02475b36
2
)()(Power3
32
1AV
velocityareadensity
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Ws
mNP
s
mN
s
m
s
mkg
s
mkg
smmmkgP
24002400
240024002400
2
1042.1
23
2
323
Wind PowerExample, cont.
Theoretical Maximum
Betz Limit: 59.3% of the theoretical is the maximum amount
extractable by a wind energy conversion device (WEC)
WWPBetz 2.1423)2400(593.0 Practical Maximum
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Wind Turbine Size-Power Comparison
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Wind Turbine Configurations
HAWT
VAWT
Boyle, G., Renewable Energy, 2nd ed., Oxford
University Press, 2004
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Configuration Tradeoffs
Factors
Efficiency Power produced per unit cost
Directionality
Support configuration Speed of rotation
Reliability
Cost Maintainability
Which type is best, HAWT or VAWT?
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Common HAWT Construction
Rotor
Blades are connected to a hub, which is connected to a shaft
Rotational speed will depend on blade geometry, number of blades,
and wind speed (40 to 400 revolutions per minute typical speed
range)
Gear box needed to increase speed to 1200-1800 RPM for generator
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Aerodynamics of Wind Turbine BladesForces are transmitted from a moving
fluid to an object in the flow streamLift = the force component perpendicular
to the original flow direction
Drag = the force component in line with
the original flow direction
Lift
Drag
http://www.grc.nasa.gov/WWW/K-12/airplane/newton3.html
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Two Types of Turbine DesignsDrag Designs
Savonius
Lift Designs
VAWT Darrieus
Most HAWT
designs
http://upload.wikimedia.org/wikipedia/commons/9/9e/Darrieus.jpg
http://upload.wikimedia.org/wikipedia/commons/9/99/Savonius_Querschnitt.png
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Aerodynamics of HAWT Blade
Boyle, G., Renewable Energy, 2nd ed., Oxford University Press, 2004
r[L(sinf - D(cosf)] = TorqueTorque x rotational speed= Power
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Aerodynamics of HAWT Blade, cont.Angle of attack, a (blade angle between chord and relative winddirection)
Has a large effect on the lift and dragTypical values between 1 and 15 degrees (what is optimum?)
D i f HAWT T bi Bl d
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Design of HAWT Turbine Blade
5-station design as seen from the tip
The blade twists to keep angle of attack constant
Blade size and shape
D i f HAWT T bi Bl d
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Design of HAWT Turbine Blade, cont.Number of blades
Increasing the number
of blades tends to
increase the
aerodynamic efficiency
Increasing the number
of blades increases the
cost (material and
manufacturing
Turbines with fewer
blades
tend to run most
efficientlyat lower tip speed ratios
(ratio of tip speed to wind
speed)
http://en.wikipedia.org/wiki/Wind_turbine_design
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R f
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References
http://www.bbc.co.uk/weather/
http://www.aos.wisc.edu/~hopkins/aos100/sfc-anl.htm
http://ww2010.atmos.uiuc.edu/(Gh)/g
uides/mtr/prs/hghdef.rxml http://en.wikipedia.org/wiki/Wind_tur
bine_design
http://www.grc.nasa.gov/WWW/K-12/airplane/short.html
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