WindTurbineBladeDesign

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Wind Turbine

Blade Design

Classroom Activities for

Wind Energy Science

Joseph Rand

Program Coordinator

The Kidwind Project

[email protected]

877-917-0079


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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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OrientationTurbines can be categorized into two overarching

classes based on the orientation of the rotor

Vertical Axis Horizontal Axis


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Calculation of Wind Power

Power in the wind

Effect of swept area, A

Effect of wind speed, V

Effect of air density, R

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 some

benefits of lighter design Higher speed means more

noise, visual, and wildlifeimpacts

Blades easier to installbecause entire rotor can be

assembled on ground Captures 10% less energythan two blade design

Ultimately provide no costsavings


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Number of Blades - Two

Advantages &

disadvantages similar to

one blade

Need teetering hub andor 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

Wood

Wood Strong, light weight,

cheap, abundant,flexible

Popular on do-ityourself 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 ratiovaries as well

To optimize angle ofattack 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 thespeed 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

V

TSR =Where,

= rotational speed in radians /sec

R= Rotor Radius

V= Wind Free Stream Velocity

R

R


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Performance Over Range of Tip

Speed Ratios

Power Coefficient Varies with Tip Speed Ratio

Characterized by Cp vs Tip Speed Ratio Curve

0.40.30.20.10.0

Cp

121086420Tip Speed Ratio


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Betz LimitAll wind power cannot

be captured by rotor

or air would be

completely still behind

rotor and not allow

more wind to passthrough.

Theoretical limit of rotor

efficiency is 59%

Most modern windturbines are in the 35

45% range


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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 experiments

and design different windturbine 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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WindTurbineBladeDesign

Documents