2009 MESA Nationals

1. 2009 MESA Nationals Windmill Pilot Project Patrick Rinckey Leonard Vance 25 October 2008

2. 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)

3. Windmill • Used to grind grain or pump groundwater • Predecessor to modern turbines of an electric society

4. 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

5. 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

6. VAWT

7. 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

8. Figure 2 Competition – Middle School • Device pulls vehicle through speed zone • Vehicle weighs 200 grams (+/- 2 grams) • Fastest vehicle speed determines score

9. 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

10. 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.

11. 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.)

12. 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.

13. 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!

14. 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

15. 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

16. 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)

17. 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

18. 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

19. 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)

20. Questions?