2009 mesa nationals
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2009 MESA Nationals. Windmill Pilot Project Patrick 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). - PowerPoint PPT PresentationTRANSCRIPT
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?