WidWise Educatio Wid Eergy Activities for Studets Cotets LESSON 10: WHICH BLADES ARE BEST? Forward...1 Itroductio...7 Uit 1: Eergy...17 Uit 2: Wid... 75 Uit 3: Turbies.... 147 Lesso 8 How Does a Widmill Work?...149 Lesso 9 How Does a Geerator Work?...161 Lesso 10 Which Blades Are Best?...177 Lesso 11 How Ca I Desig Better Blades?...191 Appedix: Advaced Wid Turbie Blade Desig ad Airfoils...201 Appedix to Uit 3 Usig WidWise to prepare for a KidWid Challege...207 Uit 4: Wid & Wildlife...215 Uit 5: Sitig Wid Turbies... 273 WidWise Educatio Curriculum Copyright 2011 WidWise Educatio Secod Editio with ew material copyright 2012 WidWise Educatio Third Editio with ew material copyright 2015 WidWise Educatio Reproductio of this curriculum is prohibited except for studet use i the classroom. For iformatio o obtaiig curriculum materials ad to lear more about the WidWise Educatio program, go to www.kidwid.org ISBN 978-1-4951-4354-0
TURBINES LESSON 10 WHICH BLADES ARE BEST? KEY CONCEPT Studets lear through experimetatio how differet blade desigs are more efficiet at haressig the eergy of the wid. TIME REQUIRED 1 2 class periods GRADES 6 8 9 12 SUBJECTS Physics Techology/Egieerig Mathematics www.kidwid.org BACKGROUND The blades of a wid turbie have the most importat job of ay wid turbie compoet ; they must capture the wid ad covert it ito usable mechaical eergy. Over time, egieers have experimeted with may differet shapes, desigs, materials, ad umbers of blades to fid which work best. This lesso explores how egieers determie the optimal blade desig. OBJECTIVES At the ed of the lesso, studets will: uderstad how wid eergy is coverted to electricity kow the process of scietific iquiry to test blade desig variables be able to collect, evaluate, ad preset data to determie which blade desig is best uderstad the egieerig desig process METHOD Studets will use wid turbie kits to test differet variables i blade desig ad measure the power output of each. Each group of studets will isolate oe variable of wid turbie blade desig, the collect ad preset data for that variable. If time allows, studets ca use their collected data to desig a optimal set of wid turbie blades usig the ext lesso, How Ca I Desig a Better Blade? MATERIALS You will eed oe set of the followig materials for each group: 1 model turbie o which blades ca quickly be iterchaged 1 multimeter or voltage/curret data logger 1 box fa Milk cartos, PVC pipe, or paper towel rolls (optioal) Ruler Pictures of wid turbie blades Sample blades of varyig sizes, shapes, ad materials Balsa wood, corrugated plastic, card stock, paper plates, etc. ¼" dowels Duct tape ad/or hot glue Scissors Protractor for measurig blade pitch Safety glasses Poster-size graph paper (optioal) Studet readig passages ad studet worksheets* *icluded with this activity Additioal Resources for every lesso ca be foud at http://lear.kidwid.org/widwise/. Resources iclude presetatios, videos, extesio activities, ad other materials. 177
WHICH BLADES ARE BEST? REDUCE DRAG More Drag Less Drag GETTING READY Studets should already have a basic uderstadig of wid eergy, icludig the followig: what a wid turbie is the fudametal parts of a wid turbie how wid turbies trasform eergy from the wid basic variables that impact turbie performace Most of this backgroud was covered i the lesso How Does a Widmill Work? The additioal resources listed at the ed of this lesso also provide helpful iformatio. The Blade Desig PowerPoit foud i the Additioal Resources sectio will also be helpful for this lesso. This slideshow features descriptios of differet blade desigs ad close-up pictures of wid turbie blades. Set up a safe testig area. Clear this area of debris ad materials. Make sure the ceter of the fa is aliged with the ceter of the wid turbie. If you are workig with multiple turbies, set them up so studets will ot be stadig i the plae of rotatio of a earby turbie. Prepare three or four simple blade sets as samples for studets to begi to see several variables ad figure out how to build blades. Make sure the sample blade sets display differet blade variables, such as legth, material, ad umber of blades. Make copies of worksheets. ACTIVITY Step 1: Begiig questios for studets What do you thik makes oe turbie work better tha aother? What variables affect the amout of power a turbie ca geerate? Do some variables matter more tha others? (For example, is turbie height more importat tha the umber of blades?) What do moder wid turbie blades look like? Is this similar to those o older widmills? Why? How may blades do most wid turbies have? What do you thik would happe with more or fewer blades? Step 2: Braistorm blade variables Provide studets with photos of differet turbie desigs, usig the Blade Desig PowerPoit or other photos foud i the Additioal Resources. Ask studets to braistorm some of the variables that affect how much eergy the blades ca capture while they are lookig at the photos. www.kidwid.org Variables may iclude: blade legth umber of blades weight/distributio of weight o blade blade pitch/agle blade shape blade material blade twist 178 Lesso 10
WHICH BLADES ARE BEST? Step 3: Determiig variables Orgaize studets ito small groups. Four studets per group is optimal. Give each studet a worksheet. Have each group select oe variable to test. Legth, umber, pitch/agle, ad shape are easy variables to test, but studets ca come up with additioal variables as well. Before costructig blades, groups should determie what eeds to be held costat i order to effectively test their variables. If you are coductig this exercise as a demostratio, ask studets which variable will perform better ad why before testig it. Studets will complete their worksheets while the teacher tests each variable. Studets ca take turs attachig blades or readig the multimeter. Step 4: Buildig blades Depedig o the variable beig tested, some groups will have to build multiple sets of blades, while other groups will oly build oe set. For example, the group testig blade material will have to build oe set of idetical blades with each material beig tested. The group testig pitch/agle, however, will oly build oe set of blades ad the test the agle of these blades o the turbie. Groups should collect their blade materials, the work together to costruct blades. Step 5: Testig blades The group will attach each set of blades to the turbie ad test it at both high ad low wid speeds. The group ca chage wid speed by movig the turbie away from the fa or turig the fa lower. Wid comig from a fa is very turbulet ad does ot accurately represet the wid a turbie would experiece outside. To clea up this turbulet wid, studets ca make a wid tuel by buildig a hoeycomb i frot of the fa usig milk cartos, PVC pipe, or paper towel rolls. This will slow the wid comig off the fa, but it will also straighte it out. BLADE PITCH Blade pitch is the agle of the blades with respect to the plae of rotatio. The pitch of the blades dramatically affects the amout of drag experieced by the blades. Efficiet blades will provide maximum torque with miimum drag. Measure pitch with a protractor. 0º 45º 90º Be sure studets uderstad what blade pitch (agle) is ad how they will measure it or keep it costat. This cocept was itroduced i How Does a Widmill Work? Make sure that studets keep pitch costat while testig other variables or the results ca be problematic. Studets will measure the voltage with a multimeter ad record their data o the worksheet. If time permits, ask studets to do three replicatios of each variable ad average their results. Step 6: Aalysis Oce studets have collected their data, tell them to aswer the questios o the worksheet ad make a graph of their data to preset to the class. If poster-size graph paper is available for studets, ask them to replicate the graph o this paper for their presetatios. www.kidwid.org Lesso 10 179
WHICH BLADES ARE BEST? CAUTION! Do ot stad i the plae of rotatio of the rotor! You could be hit if your blade flies off durig testig. The spiig rotor blades ad metal rod ca be dagerous. Make sure studets work with cautio. Be careful whe workig with the metal rod. Do ot swig or play with the rod! The eds ca be protected with tape, foam, cork, etc. Wear safety glasses whe testig widmills. Safety glasses must be wor ay time blades are spiig. Stad behid or i frot of the plae of rotatio - ad wear safety glasses! Step 7: Presetatio Each group will have five miutes to preset its data to the class. Studets should discuss their variables, how they desiged the blades, ad the results. Ask all the studets to record the results from each group o their worksheets so they have all of the class results. Step 8: Wrap up Wrap up the lesso with some of the followig questios: What variable has the greatest impact o power output? What type of blades worked best at low speeds? High speeds? What umber of blades worked best? What shapes worked best? What legth worked best? What problems did you ecouter? Did loger blades bed backward i the wid? Was this a problem? What happeed whe the diameter of the turbie rotor was bigger tha the diameter of the fa? Ask studets to aalyze the class data ad describe a optimal blade desig. If time permits, this ca be used as a startig poit for the extesio lesso: How Ca I Desig a Better Blade? EXTENSION The followig extesio may be made for grades 9 12: Ask studets to also collect amperage data ad calculate power. Discuss voltage, amperage, ad power ad how they relate to oe aother. Ask studets to determie the efficiecy of their turbies. The efficiecy of a turbie is a compariso betwee the theoretical power available i the wid ad the actual power output of the turbie. To calculate the theoretical power i the wid, studets ca use this equatio: P = ½ ρ (π r 2 )V 3 P = total power available i the wid ρ = air desity (1.23 kg/m 3 at sea level) π = pi (3.14) r = rotor radius (legth of oe blade) V = velocity of the wid Turbie efficiecy is equal to the total power output of the turbie divided by the theoretical power available. Do ot be surprised if your efficiecy is uder 5 percet. The maximum theoretical efficiecy of a wid geerator is 59 percet. Research Betz Limit to lear more about this. www.kidwid.org 180 Lesso 10
WHICH BLADES ARE BEST? VOCABULARY amperage A measure of the rate of flow of electrical charges. 1 ampere = 1 volt = 1 watt or I amp = V = P 1 ohm 1 volt R V blade pitch Agle of the blades with respect to the plae of rotatio. (Blades perpedicular to the ocomig wid would be 0 degrees. Blades parallel to the wid would be 90 degrees). drag I a wid turbie, also called wid resistace. The frictio of the blades agaist air molecules as they rotate. Drag works agaist the rotatio of the blades, causig them to slow dow. lift A force ecoutered by the blades that is perpedicular to the ocomig flow of air. Lift is a force workig to speed up the rotatio of the blades. multimeter A electroic istrumet that ca measure voltage, curret, ad resistace. power The rate at which eergy chages form from oe form to aother, or the rate at which work is doe voltage The electrical pressure or potetial differece that drives the electric curret. 1 volt = 1 amps 1 ohm = 1 watts / 1 amps wattage the metric uit of power. I electricity, oe watt of power is equal to oe ampere of electric curret beig forced to move by oe volt of potetial differece. Oe watt is also equivalet to oe joule of eergy per secod. 1 watt = 1 volt 1 amp. RELATED ACTIVITIES Lesso 8: How Does a Widmill Work? Lesso 11: How Ca I Desig Better Blades? Advaced Blades Appedix USE A MULTIMETER WITH YOUR WIND TURBINE Studets eed to kow how to record voltage ad amperage with a simple multimeter. Make sure you have doe this yourself ad ca explai it to the studets. It is importat to esure that the uits are correct. If you multiply volts by milliamps, you will get a cofusigly large ad icorrect umber for power. It is okay to just record voltage, which ca make thigs easier. Small DC motors do ot produce much power whe spu slowly. A wid turbie without gears will ot get more tha 2 volts. O a wid turbie with gears, power output ca be icreased (2 8 volts) usig gears to spi the shaft of the geerator faster tha the hub. For videos o usig a multimeter see additioal resources at http://lear.kidwid.org/widwise Lesso 10 181 www.kidwid.org
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Studet sheets ENERGY TRANSFERS AND CONVERSIONS IN A TURBINE Blades up to 60 m log Wid at least 8 m/s Blades rotate 12 20 RPM 1 1 2 3 4 5 75 m tall 1. Blades attached to hub (rotor spis i the wid) 2. Spis drive shaft (trasfers force to gearbox) 3. Gearbox (icreases shaft speed) 4. High speed shaft (trasfers force to geerator) 5. Geerator (coverts spiig shaft to electricity) 6. Wires to grid (provides electricity) 6 Lesso 10 www.kidwid.org 183
Studet sheets Name Date Class Variable What variable will you test for your experimet? Costats What variables do you have to keep the same (costat) as you perform this experimet? Experimetal desig Describe how you will perform this experimet. 1. What materials will you use? 2. How may times will you test your variable? 3. How log will you ru the test? 4. How will you chage your variable? 5. What will you use to measure your output? Hypothesis 1. What do you thik will happe? 2. Why do you thik this will happe? 184 www.kidwid.org Lesso 10
Studet sheets Data tally sheet : grades 6 8 VARIABLE (e.g., legth, i cm) LOW SPEED VOLTAGE (mv or V) HIGH SPEED VOLTAGE (mv or V) Graph your data Voltage output Variable tested (legth, umber, etc.) Lesso 10 www.kidwid.org 185
Studet sheets Data tally sheet: grades 9 12 LOW SPEED VARIABLE VOLTAGE (e.g., legth, i cm) (mv or V) AMPERAGE (ma or A) (V A) = POWER (mw or W) HIGH SPEED VARIABLE (e.g., legth, i cm) VOLTAGE (mv or V) AMPERAGE (ma or A) (V A) = POWER (mw or W) Graph your data Voltage output Variable tested (legth, umber, etc.) 186 www.kidwid.org Lesso 10
Studet sheets Name Date Class What happeed? 1. How did the voltage chage as a result of maipulatig the variable? 2. What was the optimal settig for the variable that you tested? 3. Do you thik that the variable that you tested has a large or small effect o how much power the turbie ca make? 4. What problems did you ecouter as you performed your experimets? How could you fix these problems? Lesso 10 www.kidwid.org 187
Studet sheets Class results Record the results from the class experimets i the table below. Power = Voltage (V) Curret (A) Make sure you are recordig volts ad amps (ot milliamps). 1 A=1,000 ma VARIABLE VOLTAGE (V) AMPERAGE POWER OUTPUT (e.g. legth cm) (extesio) (ma or A) (optioal) (mw or W) 15 cm 1.7 100 ma 0.17 W 1. If you were a lead desig egieer, what would you recommed your compay do to their turbie blades based o the class results? Why? 188 www.kidwid.org Lesso 10
Aswer sheets Variable What variable will you test for your experimet? Aswers will vary. Example variables: Blade pitch, blade shape/size, material of blades, umber of blades, etc. Costats What variables do you have to keep the same (costat) as you perform this experimet? Aswers will vary. Example variables: Blade pitch, blade shape/size, material of blades, umber of blades, etc. Experimetal desig Describe how you will perform this experimet. 1. What materials will you use? Aswers will vary. Balsa, corrugated plastic, paper plates, cardboard, etc. 2. How may times will you test your variable? Variables should be tested at least twice. 3. How log will you ru the test? Aswers will vary. Trials should last at least 20 secods. 4. How will you chage your variable? Aswers will vary. 5. What will you use to measure your output? Output should be recorded usig a multimeter or other quatitative measuremet. Hypothesis 1. What do you thik will happe? Studets should hypothesize about how chagig their chose variable will affect the power output of the wid turbie. 2. Why do you thik this will happe? Studets should explai why they thik chagig the variable will affect power i this way. What happeed? 1. How did the voltage chage as a result of maipulatig your variable? Chagig the variable should cause the voltage to icrease or decrease. 2. What was the optimal settig for the variable that you tested? Which trial yielded the most voltage? For example, if the test variable is blade pitch, studets may aswer Blades pitched at 20 degrees produced the most voltage. 3. Do you thik that your variable has a large or small effect o how much power the turbie ca make? Aswers will vary. Lesso 10 www.kidwid.org 189
Aswer sheets 4. What problems did you ecouter as you performed your experimets? How could you fix these problems? Aswers will vary. Oe commo problem is that it is hard to keep all other variables costat while testig oe specific variable. Class results Record the results from the class experimets i the table below. Power = Voltage (V) Curret (A) 1. If you were a lead desig egieer, what would you recommed your compay do to their turbie blades based o the class results? Why? Studets should describe the optimal blade desig based o class results. This aswer should discuss at least three variables e.g., legth of blades, umber of blades, blade pitch, blade material, etc. 190 www.kidwid.org Lesso 10