2009 MESA NationalsWindmill Pilot ProjectPatrick Rinckey

Leonard Vance

25 October 2008

Types of Wind Turbines There are more types of wind turbines out

there than just the classic windmill style. Classic Windmill Horizontal Axis Wind Turbine (HAWT) Vertical Axis Wind Turbine (VAWT)

Windmill Used to grind grain or pump groundwater Predecessor to modern turbines of an electric

society

HAWT Blades face into wind and track to

wind direction Usually 2 or 3 blades Main Advantage

Blades can be faced directly into the wind and are 50% more efficient than a VAWT

Main Disadvantage Poor performance in turbulent wind and

close to the ground

VAWT Blades are vertical and can be designed in a variety

of ways Usually 2 or 3 blades, possibly more Main Advantages

Wind can come from any direction without needing to change the blade position, low cut-in speed, better performance near the ground

Main Disadvantage Because some blades are fighting agianst the wind, it’s

about 50% as efficient

VAWT

Competition Setup Setup

Fan will be set to High (3.31 m/s) for both competitions

Device must be >75cm from fan

Device must be in device area Device may hang over table

surface

Figure 1

Competition – Middle School Device pulls vehicle

through speed zone Vehicle weighs 200

grams (+/- 2 grams) Fastest vehicle speed

determines score

Figure 2

Competition – High School Device aimed at position 1 Device turning a load After 30 seconds to spin up,

RPM measurement of load is taken

Fan moved to position 2 After 30 seconds, measurement

is taken Speed 1 + Speed 2 must be

close to 60 rpm Figure 4

Competition – High School cont Device may turn the disk on

it’s main axis or a secondary axis.

The secondary axis will incur a friction loss, but may be easier to control the load speed. Figure 5

Things to consider Rotational Mass

Rotational inertia should be minimized to have a fast spin-up time. This means while the load is fixed, the turbine should be made as light as possible but still durable. This will allow a faster spin-up time because there is less inertia to overcome

Friction Having low friction along the turbine shaft is essential to

having a fast spin up time. Look for materials which have low coefficients of friction against one another as well as lubricants (teflon, graphite etc.)

Things to consider Betz Limit

As air flows through the turbine blades, it creates a pressure gradient where the pressure is higher in front of the blades than behind them, deflecting airflow around the blades instead of through them

a = Vf – Vb / Vf

Vf = Velocity of wind stream from afar Vb = Velocity of wind through the blades a = axial induction factor which Betz derived to be 1/3

for an optimal wind turbine design.

Box Fans Produce Substantially Imperfect Wind Distributions

Wind varies substantially in both direction and magnitude as you move about the table

A telltale will help you understand this

Note: You will want a turbine that rotates the same direction as the fan

Turbine Size and Placement appear to be important – Remember Power goes as wind velocity cubed!

75 cm 50 cm

20” Box Fan Wind & Power levels

-40 -30 -20 -10 0 10 20 30 400

10

20

30

40

50

60

horizontal distance (cm)

vert

ical

dis

tanc

e (c

m)

-40 -30 -20 -10 0 10 20 30 400

10

20

30

40

50

60

horizontal distance (cm)

vert

ical

dis

tanc

e (c

m)

Total Power Available = 6.46 W

Max Velocity = 4.4 m/s

Extent of Propeller Fan

Wind Velocity Distribution Relative Power Distribution

Power Available = ½ * air density * (velocity)3 * area of flow

Min Velocity = 0 m/s

Definitions of Torque and Angular Rate

Fload

r

Torque = Fload * rLoad torque comes from multiplying the drag (or load) force times the radius of the spindle

Angular rate (commonly , or omega) is the spin rate of the turbine in radians/sec

= RPM *(2)/60

Where RPM is the spin rate of the turbine in revolutions per minute

Power = Torque *

This is what you’re trying to maximize

Dynamometer Optimizes Power Output

Power = Torque * Angular rate

As you increase load torque, turbine angular rate slows, eventually stopping it.Angular rate is zero – No Power.

As you decrease load torque to zero, the turbine spins quicklyLoad Torque is zero – No Power

The optimum is somewhere in between, but where?

A dynamometer measures power,establishing the optimum speed forany turbine P

ower

(W

atts

)

Turbine Speed (rad/s)00

Optimal Speed

Free Spinning Turbine

Loa

d T

orq

ue

(Nm

)

Simple Equations for Dynamometer

mcw

r

mref

357 g

Fscale

Postal Scale

Fcw= Fload+ Fref - Fscale

Fload Fcw= mcw* gFscale= mscale* g

Fload= Fcw+ Fscale - Fref

Fref= mref* g

Fload= g*(mcw+ mscale – mref)

turbine

Fcw: Weight of Counterweight (N)Fload: Drag on Turbine Spindle (N)Fref: Weight of Reference object (N)Fscale: Weight on scale (N)

mcw: Mass of Counterweight (kg)mref: Mass of Reference object (kg)Fscale: Mass measured by scale (kg)r: Spindle radius (m): angular rate of turbine (rad/s)g: local gravity (= 9.81 m/s2)

or…

From chart 3…

Power = Torque *

Power = g*(mcw+ mscale – mref)*r*

Torque = Fload*r (from chart 3) so…

Plugging in…

1) Choose a (fairly heavy) reference mass2) Choose a counterweight mass3) Measure turbine speed4) Measure scale mass5) Calculate power6) Go to step 2, repeat

An Earlier Wind Power Experiment…

This experiment was to see how fast a wind powered car could go straight into the wind.

This turbine was then adapted to today’s demonstration

0 2 4 6 8 10 12 14 160

1

2

0 2 4 6 8 10 12 14 160

0.1

0.2

Power Output Measurements

Angular Rate (rad/sec)

Pow

er (

Wat

ts)

Loa

d T

orqu

e (N

ewto

n m

eter

s)

Optimal power (1.05 W) at 9.5 rad/s angular rate Efficiency = Power Output

Power Available

Efficiency = 1.05 W 6.48 W

= 16.3%

Demonstration turbine shows 16.3% efficiency

There’s Room for Improvement!

Questions?