www.kidwind.orgwww.kidwind.org
KidWind Project | www.kidwind.org
KidWind Project | www.kidwind.org
What is KidWind?
 The KidWind Project is a team of teachers, stdents, engineers and !ractitioners e"!loring the science #ehind wind energy in classrooms
arond the $%. 'r goal is to introdce as many !eo!le as
!ossi#le to the elegance of wind !ower throgh hands(on science acti)ities which are challenging,
engaging and teach #asic science !rinci!les.
 
'rientation  Tr#ines can #e categori*ed into two
o)erarching classes #ased on the orientation of the rotor
  Vertical Axis Horizontal Axis
Advantages • 'mnidirectional
 – cce!ts wind from any angle
• -om!onents can #e monted at grond le)el  – Ease of ser)ice  – ighter weight towers
• -an theoretically se less materials to ca!tre the same amont of wind
Disadvantages • /otors generally near
• Poor self(starting ca!a#ilities
• /e0ires s!!ort at to! of tr#ine rotor
• /e0ires entire rotor to #e remo)ed to re!lace #earings
• ')erall !oor !erformance and relia#ility
• 1a)e ne)er #een
aerofoil #lades  – 5ore e6cient
c! sha!es are !shed #y the wind
 
+WT’s ha)e not #een commercially sccessfl, yet:
E)ery few years a new com!any comes along !romising a re)oltionary #reakthrogh in wind tr#ine design that is low cost, ot!erforms anything else on the market, and o)ercomes all of the !re)ios !ro#lems with +WT’s.  They can also sally #e installed on a roof or in a city where wind is !oor.
Wind%tor 5ag(Wind
WindTree Wind Wandler
F   a  c t   o r 
 
1ori*ontal "is Wind Tr#ines
• /otors are sally $!(wind of tower
 
cti)e )s. Passi)e  ;aw
• cti)e ;aw <all medim & large tr#ines !rodced today, & some small tr#ines from Ero!e=  – nemometer on nacelle
tells controller which way to !oint rotor into the wind
 –  ;aw dri)e trns gears to !oint rotor into wind
• Passi)e ;aw <5ost small tr#ines=  – Wind forces alone direct
rotor
KidWind Project | www.kidwind.org
irfoil >omenclatre wind tr#ines se the same aerodynamic !rinci!als as
aircraft
ift & 2rag orces
•  The Lift Force is !er!endiclar to the direction of motion. We want to make this force @AB.
 
hord line and the diretion o the relative
wind$ VR %
VR = wind s&eed seen #' the airoil – vetor
sum o V (ree stream wind) and ΩR (ti&
s&eed)%
 
 Ti!(%!eed /atio
 Ti!(s!eed ratio is the ratio of the s!eed of the rotating #lade ti! to the s!eed of the free stream wind.
 There is an o!timm angle of attack which creates the highest lift to drag ratio.
@ecase angle of attack is de!endant on wind s!eed, there is an o!timm ti!(s!eed ratio
ΩR
R = Rotor Radius
 
C Power -oe6cient +aries with Ti! %!eed /atio
C -haracteri*ed #y -! )s Ti! %!eed /atio -r)e
0%*
0%+
0%,
 Twist &  Ta!er• %!eed throgh the air
of a !oint on the #lade changes with distance from h#
•  Therefore, ti! s!eed ratio )aries as well
 
• Pitch -ontrol  – @lades rotate ot of
the wind when wind s!eed #ecomes too great
• %tall -ontrol  – @lades are at a D"ed
!itch that starts to stall when wind s!eed is too great
 – Pitch can #e adjsted for !articlar location’s wind regime
• cti)e %tall -ontrol  – 5any larger tr#ines
 
irfoil in stall
C %tall arises de to se!aration of ow from airfoil
C %tall reslts in decreasing lift coe6cient with increasing angle of attack
C %tall #eha)ior com!licated de to #lade
 
!lanform area to total swe!t area
ow solidity <F.7F= G high s!eed, low tor0e
1igh solidity <HF.IF= G low s!eed, high tor0e
R
A
a
Rotor Wake
Rotor Disc
ll wind !ower cannot #e ca!tred #y rotor or air wold #e com!letely still #ehind rotor and not allow more wind to !ass throgh.
 Theoretical limit of rotor e6ciency is 8J9
 
>m#er of @lades 'ne
• /otor mst mo)e more ra!idly to ca!tre same amont of wind  – Bear#o" ratio redced  – dded weight of
conter#alance negates some #eneDts of lighter design
 – 1igher s!eed means more noise, )isal, and wildlife im!acts
• @lades easier to install #ecase entire rotor can #e assem#led on grond
• -a!tres 7F9 less energy than two #lade design
• $ltimately !ro)ide no cost sa)ings
 
• d)antages & disad)antages similar to one #lade
• >eed teetering h# and or shock a#sor#ers #ecase of gyrosco!ic im#alances
• -a!tre 89 less energy than three #lade designs
 
• @alance of gyrosco!ic forces
& transmission costs
 
 – Po!lar on do(it yorself tr#ines
• %olid !lank • aminates • +eneers • -om!osites
 
easy to work with
 
• ightweight, strong, ine"!ensi)e, good fatige characteristics
• +ariety of manfactring !rocesses  – -loth o)er frame
 – Pltrsion
• 5ost modern large tr#ines se D#erglass
 
1#s
 The h# holds the rotor together and transmits motion to nacelle
 Three im!ortant as!ects • 1ow #lades are attached
 – >early all ha)e cantile)ered h#s <s!!orted only at h#=
 – %trts & %tays ha)en’t !ro)ed worthwhile
• i"ed or +aria#le Pitch? • le"i#le or /igid
ttachment  – 5ost are rigid  – %ome two #laded
designs se teetering h#s
 
• 2irect 2ri)e <no transmission=  – Lieter & more
relia#le  – 5ost small tr#ines
• 5echanical  Transmission  – -an ha)e !arallel or
!lanetary shafts  – Prone to failre de
to )ery high stresses  – 5ost large tr#ines
<e"ce!t in Bermany=
BE N.O 5W <a#o)e=
5lti(dri)e -li!!er i#erty N.8 5W <right=
 
 
 
 
 
 
controls  – @lade tter
mo)es to redce frontal area facing wind
 – -oning <downwind= rotor #lades come to a shar!er cone
 – Passi)e !itch go)ernors #lades !itch ot of wind
 
 Towers
• 5ono!ole <>early all large tr#ines=  – T#lar %teel or
-oncrete
• attice <many 5edim tr#ines=  – NF ft. sections
• Byed  – attice or mono!ole
• O gys minimm
 – Tilt(! • gys