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

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 = V f – V b / V f V f = 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 Total Power Available = 6.46 W Max Velocity = 4.4 m/s Extent of Propeller Fan Wind Velocity DistributionRelative Power Distribution Power Available = ½ * air density * (velocity) 3 * area of flow Min Velocity = 0 m/s

Definitions of Torque and Angular Rate F load r Torque = F load * r Load 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 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 Power (Watts) Turbine Speed (rad/s) 0 0 Optimal Speed Free Spinning Turbine Load Torque (Nm)

Simple Equations for Dynamometer m cw r m ref 357 g F scale Postal Scale F cw = F load + F ref - F scale F load F cw = m cw * g F scale = m scale * g F load = F cw + F scale - F ref F ref = m ref * g F load = g*(m cw + m scale – m ref )  turbine F cw : Weight of Counterweight (N) F load : Drag on Turbine Spindle (N) F ref : Weight of Reference object (N) F scale : Weight on scale (N) m cw : Mass of Counterweight (kg) m ref : Mass of Reference object (kg) F scale : Mass measured by scale (kg) r: Spindle radius (m)  : angular rate of turbine (rad/s) g: local gravity (= 9.81 m/s 2 ) or… From chart 3… Power = Torque *  Power = g*(m cw + m scale – m ref )*r*  Torque = F load *r (from chart 3) so… Plugging in… 1)Choose a (fairly heavy) reference mass 2)Choose a counterweight mass 3)Measure turbine speed 4)Measure scale mass 5)Calculate power 6)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

Power Output Measurements Angular Rate (rad/sec) Power (Watts) Load Torque (Newton meters) 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?