Wind Turbine Design

Design of Wind Turbines

GK-12 Wind Energy and Aerospace WorkshopJuly 13th 24th, 2009

Wind Turbine Design

Number of Blades: One

Rotor must move more rapidly to capture same amount of wind Gearbox ratio reduced Added weight of

counterbalance negates some benefits of lighter design

Higher speed means more noise, visual, and wildlife impacts

Blades easier to install because entire rotor can be assembled on ground

Captures 10% less energy than two blade design

Ultimately provide no cost savings

Wind Turbine Design

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

Wind Turbine Design

Number of Blades: Three

Balance of gyroscopic forces

Slower rotation increases gearbox &

transmission costs More aesthetic, less

noise, fewer bird strikes

Wind Turbine Design

Blade Material: Wood

Wood Strong, light weight,

cheap, abundant, flexible

Popular on do-it yourself turbines

Solid plank

Laminates

Veneers

Composites

Wind Turbine Design

Blade Material: Metal

Steel Heavy & expensive

Aluminum Lighter-weight and easy to

work with Expensive Subject to metal fatigue

Wind Turbine Design

Blade Material: Fiberglass

Lightweight, strong, inexpensive, good fatigue characteristics

Variety of manufacturing processes Cloth over frame Pultrusion Filament winding to

produce spars

Most modern large turbines use fiberglass

Wind Turbine Design

Lift & Drag

The Lift Force is perpendicular to the direction of motion. We want to make this force BIG.

The Drag Force is parallel to the direction of motion. We want to make this force small.

= low

= medium

Wind Turbine Design

AirfoilJust like the wings of an airplane, wind turbine blades use the airfoil shape to create lift and maximize efficiency.

Wind Turbine Design

Twist & Taper Twist from blade root to the tip is

used to optimize the angle of attack all along blade and result in a constant inflow along the blade span

Taper is used to reduce induced drag and increase the L/D ratio

Wind Turbine Design

Tip-Speed Ratio

Tip-speed ratio is the ratio of the speedof the rotating blade tip to the speed of the free stream wind.

There is an optimum angle of attackwhich creates the highest lift to dragratio.

Because angle of attack is dependant onwind speed, there is an optimum tipspeed ratio

RVTSR =

Where, = rotational speed in radians /secR = Rotor RadiusV = Wind Free Stream Velocity

R

R

Wind Turbine Design

Power Coefficient vs Tip Speed Ratio

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

12 10 8 6 4 2 0 Tip Speed Ratio

Wind Turbine Design

Betz Limit All wind power cannot be captured by rotor or airwould be completely still behind rotor and not allow more wind to pass through. Theoretical limit of rotor efficiency is 59%

Most modern wind turbines are in the 35 45% range

Wind Turbine Design

Calculation of Wind Power

Effect of swept area, A Effect of wind speed, V Effect of air density,

R

Swept Area: A = R2Area of the circle swept by the rotor (m2).

Power in the Wind = AV3

PresenterPresentation NotesThis is the equation for the power in the wind. (Dont fear there are only 2 equations in this presentation.) Each of the terms in this equation can tell us a lot about wind turbines and how they work. Lets look at wind speed (V), swept area (A), and density (Greek letter rho, ) one at a time.

First, lets look at wind speed, V. Because V is cubed in the equation, a small increase in V makes for a increase in power. (illustrated on next slide)

(Click on the links at the bottom to get the values of both k and .)

Wind Turbine Design

Rotor Solidity

Solidity is the ratio of total rotorplanform area to total swept area

Low solidity (0.10) = high speed, low torque

High solidity (>0.80) = low speed, high torqueA

Ra

Solidity = 3a/A

Wind Turbine Design

Wind Turbines in the Classroom Students perform experiments

and 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!

Wind Turbine Design

Wind Turbine Lessons

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

Design of Wind TurbinesNumber of Blades: OneNumber of Blades: TwoNumber of Blades: ThreeBlade Material: WoodBlade Material: MetalBlade Material: FiberglassLift & DragSlide Number 9Twist & TaperTip-Speed RatioSlide Number 12Betz Limit Calculation of Wind PowerRotor SolidityWind Turbines in the ClassroomWind Turbine Lessons