windturbinebladedesign..march.08
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Wind TurbineWind Turbine
Blade DesignBlade Design
Classroom Activities forClassroom Activities for
Wind Energy ScienceWind Energy Science
Joseph RandJoseph Rand
Program CoordinatorProgram Coordinator
The Kidwind ProjectThe Kidwind Project
[email protected]@kidwind.org
877877--917917--00790079
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What is KidWind?What is KidWind?The KidWind Project is a team of teachers, students, engineers and
practitioners exploring the science behind wind energy in classrooms
around the US. Our goal is to introduce as many people as possible to
the elegance of wind power through hands-on science activities which
are challenging, engaging and teach basic science principles.
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Orientation
Turbines can be categorized into two overarchingclasses based on the orientation of the rotor
Vertical Axis Horizontal Axis
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Calculation of Wind Power
Power in the windPower in the wind
Effect of swept area, A Effect of wind speed, V
Effect of air density, VR
Swept Area: A = R2
Area of the circle swept
by the rotor (m2).
Power in the Wind = AV3
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Number of Blades One
Rotor must move morerapidly to capture sameamount of wind
Gearbox ratio reduced Added weight of
counterbalance negates somebenefits of lighter design
Higher speed means morenoise, visual, and wildlifeimpacts
Blades easier to installbecause entire rotor can be
assembled on ground Captures 10% less energy
than two blade design Ultimately provide no cost
savings
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Number of Blades - Two
Advantages &
disadvantages similar to
one blade
Need teetering hub and
or shock absorbers
because of gyroscopic
imbalances
Capture 5% less energy
than three blade designs
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Number of Blades - Three
Balance of
gyroscopic forces
Slower rotation
increases gearbox &
transmission costs
More aesthetic, less
noise, fewer birdstrikes
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Blade Composition
WoodWood
Strong, light weight,cheap, abundant,
flexible Popular on do-it
yourself turbines
Solid plank
Laminates
Veneers
Composites
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Blade Composition
Metal
Steel
Heavy & expensive
Aluminum
Lighter-weight and easy
to work with
Expensive
Subject to metal fatigue
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Blade Construction
Fiberglass
Lightweight, strong,inexpensive, good fatiguecharacteristics
Variety of manufacturingprocesses
Cloth over frame
Pultrusion
Filament winding to produce
spars
Most modern large turbinesuse fiberglass
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Large Wind Turbines
450 base to blade
Each blade 112
Span greater than 747
163+ tons total Foundation 20+ feet deep
Rated at 1.5 5 megawatt
Supply at least 350 homes
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Lift & Drag Forces
The Lift Force isperpendicular to thedirection of motion. Wewant to make this force
BIG.
The Drag Force is parallelto the direction of motion.We want to make thisforce small.
= low
= medium
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Airfoil Shape
Just like the wings of an airplane,
wind turbine blades use the airfoil
shape to create lift and maximize
efficiency.
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Twist & Taper Speed through the air of a
point on the bladechanges with distancefrom hub
Therefore, tip speed ratio
varies as well To optimize angle of
attack all along blade, itmust twist from root to tip
Fast
Faster
Fastest
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Tip-Speed Ratio
Tip-speed ratio is the ratio of the
speed of the rotating blade tip tothe speed of the free streamwind.
There is an optimum angle of attackwhich creates the highest lift todrag ratio.
Because angle of attack is dependanton wind speed, there is anoptimum tip-speed ratio
R
VTSR =
Where,
= rotational speed in radians /sec
R= Rotor Radius
V = Wind Free Stream Velocity
R
R
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PerformanceOver Range of Tip
Speed Ratios
Power Coefficient Varies with Tip Speed Ratio
Characterized by Cp vs Tip Speed Ratio Curve
0.4
0.3
0.2
0.1
0.0
Cp
121086420
Tip Speed Ratio
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Rotor SoliditySolidityis the ratio of total rotor
planform area to total swept area
Low solidity (0.10) = high speed, low torque
High solidity (>0.80) = low speed, high torque
A
R
a
Solidity= 3a/A
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In the Classroom
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Wind Turbine Blade Challenge
Students perform experimentsand design different wind
turbine blades
Use simple wind turbine models
Test one variable while holding
others constant
Record performance with a
multimeter or other load device
Goals: Produce the most
voltage, pump the most water,
lift the most weight
Minimize Drag
Maximize LIFT
Harness the POWER of the wind!
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Measuring/Storing Power Output
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Setting Up the Blade Challenge
What You Need: Box Fan (2-4 depending on class size)
Blade Materials
Balsa
Paper/styrofoam plates/bowls
Cardstock, cardboard, corrugated plastic
Pie tins, etc.. etc.. etc (leftover junk!)
Scissors
Glue/Tape
Voltmeters, multimeters, and/or water pumps
Hubs, motors (generators), towers, dowels
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Other Challenges
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For More PowerGet Your Students to Work Together
Wire the wind turbines together in a circuit
Series vs. Parallel
Dramatic increase in power!
And make a miniature Wind Farm!
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Standards Scientific Processes
Collecting & Presenting Data
Performing Experiments
Repeating Trials
Using Models
Energy Transformations (forms of energy) Mechanical Electrical
Circuits/Electricity/Magnetism
Use of simple tools and equipment
Engineering design processes
Renewable vs. Non-Renewable resources
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Math Lessons
Tip Speed Ratio
Calculating Height Using Similar Triangles
Coefficient of Power
Swept Area
Gear Ratios
Total Power Calculations
Word Problems (economics, etc.)
Etc
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The Kidwind Project
www.kidwind.org
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