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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).
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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)
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
Figure 1 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 2 Competition – Middle School • Device pulls vehicle through speed zone • Vehicle weighs 200 grams (+/- 2 grams) • Fastest vehicle speed determines score
Figure 4 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 5 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.
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 50 cm 75 cm 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!
20” Box Fan Wind & Power levels Min Velocity = 0 m/s Wind Velocity Distribution Relative Power Distribution Extent of Propeller Fan Max Velocity = 4.4 m/s Power Available = ½ * air density * (velocity)3 * area of flow Total Power Available = 6.46 W
Definitions of Torque and Angular Rate Angular rate (commonly w, or omega) is the spin rate of the turbine in radians/sec w = RPM *(2p)/60 Where RPM is the spin rate of the turbine in revolutions per minute r Power = Torque * w This is what you’re trying to maximize Fload Load torque comes from multiplying the drag (or load) force times the radius of the spindle Torque = Fload * r
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 quickly Load Torque is zero – No Power The optimum is somewhere in between, but where? A dynamometer measures power, establishing the optimum speed for any turbine Load Torque (Nm) Power (Watts) Optimal Speed Free Spinning Turbine 0 0 Turbine Speed (rad/s)
Simple Equations for Dynamometer Fcw= Fload+ Fref - Fscale 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) w: angular rate of turbine (rad/s) g: local gravity (= 9.81 m/s2) or… wturbine Fload= Fcw+ Fscale - Fref Fcw= mcw* g Fload Fscale= mscale* g Fref= mref* g r Plugging in… mcw Fload= g*(mcw+ mscale – mref) Fscale mref From chart 3… • Choose a (fairly heavy) reference mass • Choose a counterweight mass • Measure turbine speed • Measure scale mass • Calculate power • Go to step 2, repeat Power = Torque * w 357 g Torque = Fload*r (from chart 3) so… Postal Scale Power = g*(mcw+ mscale – mref)*r*w
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
Power Output Measurements 0.2 2 Optimal power (1.05 W) at 9.5 rad/s angular rate Efficiency = Power Output Power Available Power (Watts) Load Torque (Newton meters) Efficiency = 1.05 W 6.48 W 0.1 1 = 16.3% Demonstration turbine shows 16.3% efficiency There’s Room for Improvement! 0 0 0 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 Angular Rate (rad/sec)