NOVEL AIRFOIL DESIGN FOR SMALL HORIZONTAL AXIS WIND TURBINE: A PRELIMINARY RESULT

SASEC2015 Third Southrn African Solar Enrgy Confrnc 11 13 May 2015 Krugr National Park, South Africa NOVEL AIRFOIL DESIGN FOR SMALL HORIZONTAL AXIS WIND TURBINE: A PRELIMINARY RESULT 1* Ajayi Olusyi O, 1 Okowo Opymi, 1 Aasa Samson Abiodun, 2 Aboyad Akinwal O, 3 Willoughby Alx 1 Mchanical Enginring Dpartmnt, Covnant Univrsity, P.M.B. 1023, Ota, Nigria 2 Procss, Enrgy and Environmntal Tchnology Station, Univrsity of Johannsburg, South Africa 3 Industrial Physics Dpartmnt, Covnant Univrsity, P.M.B. 1023, Ota, Ogun Stat, Nigria, E-mail & Tl: olusyi.ajayi@covnantunivrsity.du.ng; +234-8036208899 ABSTRACT Various rsarch fforts hav bn dirctd towards th dsign and r-dsign of wind turbin systms. This is in ordr to hav mor fficint, bttr prforming and cost ffctiv turbin systms. Basd on this, fforts hav bn focusd on wind turbin rotor dsign with mphasis placd on its arodynamics. This is bcaus th important critrion of a wind turbin rotor is th airfoil. It is th lmnt that producs th forcs that maks th turbin rotat. This rsarch builds on xisting knowldg and aims to furthr dpn knowldg in th fild of wind turbin rotor dsign. Th study dsignd and analysd a nw airfoil for us in a small horizontal axis wind turbin. It mployd th flow stag airfoil bhaviour togthr with analytical softwar tools that includ XFLR5, AirfoilPrp_v2.02.01, WT_Prf, and MATLAB.. Thr wll known and tstd airfoils wr mployd and th s wr intrpolatd to crat a nw, mor fficint and bttr prforming small wind turbin rotor airfoil. Th outcom showd th nw airfoil prforms bttr with good glid ratio ovr longr angl rang, chord distribution and blad twist among othr things. Th paramtrs of th nw airfoil wr such that 10.17%, 26.49%, 6.26% and 45.0% of th chord charactrisd th maximum thicknss and its position, and th maximum cambr and its position rspctivly. INTRODUCTION Th dsir to gnrat lctricity from sourcs that ar both clan and nvironmnt frindly has brought about various fforts at dvloping systms which can mploy abundant rnwabl nrgy sourcs. On of such rsourcs is th wind. It is wll known that wind nrgy has th ability to supply a substantial amount of lctrical powr to communitis, ithr as standalon and or grid connctd powr sourc [1-4]. Wind turbin dsign has gon through various dvlopmntal changs in th past yars. Ths changs hav focusd on dvloping systms that would bring down th capital cost pr kw of wind lctricity. Various attmpts hav bn mad to dvlop wind turbin systms that ar mor fficint and cost ffctiv. A good numbr of ths attmpts hav focusd on wind turbin blad dsign optimization [5-6]. Mor rcntly, fforts hav bn gard towards th dsign of turbin rotors that will oprat with maximum arodynamic prformanc. This is prdicatd on th fact that improvmnts in th arodynamic dsign hav associatd bnfits which includ good fficincy and bttr conomic prformanc [7]. Anothr major importanc of having optimum arodynamic prformanc is th associatd ability to mak wind turbin rotor blads produc at low cut-in wind spds. This is bcaus th airfoil is th most important and basic charactristic of a wind turbin blad. It is th lmnt that producs th forcs that mak th turbin rotat. Howvr, according to Singh and Ahmd [8], arodynamic optimization of th rotor blads is associatd with optimization of th chord and twist distribution, numbr of blads, choic of airfoil shap, and th tip spd ratio. With this in mind, rsarch fforts hav bn dirctd towards dtrmining th optimum rotor shap that producs dsird lctrical powr at low cut-in wind spds. This study focusd on dvloping a nw airfoil suitabl for small horizontal axis wind turbin (HAWT) that will b mor fficint with improvd prformanc at low cut-in spds. Thr ar svral familis of airfoil profils in xistnc for diffrnt applications. For instanc, thr is th vry popular National Advisory Committ for Aronautics (NACA) sris and th National Rnwabl Enrgy Laboratory (NREL), USA sris. Ths ar availabl for rsarch purposs. NREL has som airfoils that ar spcifically availabl for small wind turbins (SWT). Howvr, th stratgy adoptd in this study was to dsign/dvlop airfoils whos glid ratio is high at a rang of angls of attack rathr than just at on pak angl or fw angls. This will nhanc th prformanc of th dsignd blad bttr than othrs such as th NREL or NACA sris. Som profils of th NREL sris that hav gon through optimization procss includs FX 63-137, S822, S834, SD2030, SG6043 and SH3055 [9-10]. 181

RESEARCH METHODOLOGY Rotor Charactristics Th most important componnt of a wind turbin rotor is th airfoil. This is bcaus it is th lmnt that producs th forcs that mak th turbin rotat. Th forcs ar calld th lift (L) and drag (D) forcs and givn by th quations (1) and (2) rspctivly. Th paramtrs of utmost importanc ar th cofficints of lift (C l ) and drag (C d ). (2) whr: ρ = dnsity, s = airfoil span, v = air vlocity, c = airfoil chord. Equation (3) is calld th glid ratio. It is th most important factor that affcts th prformanc of th wind blad. Th pitching momnt cofficint (C m ) This is anothr important paramtr, apart from th cofficints of lift and drag that affcts th Rynolds numbr. It is drivd from (Manwll t al. [11]: whr: M = pitching momnt Th airfoil bhaviour Thr ar basically thr flow stags of airfoil bhaviour. Ths ar th attachd flow stag, th high lift/stall dvlopmnt stag and th flat/fully stalld stag. Howvr, small wind turbins ar gnrally dsignd in th attachd flow stag. This study thrfor mployd th attachd flow stag. Blad radius and siz This is dtrmind from quation (5): P R 1 2 vcp 2 (5) whr: R = radius, P = powr xtractd from th wind, ρ = dnsity, v = wind vlocity and C p = cofficint of powr. Chord distribution Th wind blad solidity is affctd by chord distribution. Th chord spcification at th blad tip dtrmins th magnitud of nrgy lost as a rsult of th wind vortics. Equation (6) [12] was mployd to dtrmin th chord distribution. whr: is tip spd ratio, N is th numbr of blads (= 3), is th maximum cofficint of lift and r is radius. (1) (3) (6) 4 Th chord distribution is important in th dtrmination of starting tim and also th strsss at th connction of th blad to th hub. Th closr th chord distribution is to th tip of th blad, th fastr th blad movs through th air. Hnc, th rlativ vlocity of th wind incrass with incras in radius. Blad twist ( ) This is a significant dtrmination of th cofficint of powr obtaind at ach sgmnt of th blad. Equation (7) was usd to dtrmin th dsignd blad twist [12] as: (7) whr, λ is tip spd ratio at a particular radius r. Wind spd, rotational spd and blad pitch In th dsign, th oprating conditions wr assumd to b th following: - Oprating wind spd = btwn 3 and 15 m/s - Blads rotational spd = btwn 200 and 600 rpm - Blad pitch was takn to b zro. Tools usd Th rotor charactristics ar th foundation of SWT blad dsign. Thrfor, bfor th procss of crating a wind blad bgins an airfoil must b nvisagd and slctd. This is bcaus th airfoil is th most important and fundamntal aspct of crating a wind turbin s blad. Th airfoils ar thn analysd for suitability and adaptability. Basd on this, this study mployd th XFLR5 tool to analys and study th charactristics of diffrnt airfoils with th viw to slct th bst airfoil dsign that optimally mt th dsird goal. XFLR5 is a program that analyss airfoils using th Xfoil cod dvlopd by Profssor Mark Drla of th Massachustts Institut of Tchnology. In ordr to undrstand and validat th rsults from th XFLR5, a st of diffrnt airfoils wr slctd and xamind so as to b abl to dtrmin th bnfits of th airfoil to b cratd. Th slction was basd on th critria that thy must hav data with which comparisons could b mad. Airfoils mployd in this study, and thir charactristics ar prsntd in Tabl 1. Furthr to this, th XFLR5 was usd to find th arodynamic paramtrs of th airfoils E214, S1210 and NACA 7409 and thraftr usd to crat a novl airfoil calld OP 2-3 airfoil and also dtrmin its arodynamic paramtrs. Th rsults from this srvd as input for th Microsoft Excl tool, AirfoilPrp_v2.02.01. This xcl tool was usd to prpar and procss th arodynamic paramtrs of th novl OP 2-3 airfoil for us in th program WT_Prf (Wind Turbin Prformanc). WT_Prf was dvlopd by NREL. It uss th Blad Elmnt Momntum (BEM) thory in computing th prformanc of a wind turbin. MATLAB cods wr usd to gnrat th chord distribution and twist of th wind turbin blads. Th cods wr writtn by Profssor David Wood of th Dpartmnt of Mchanical and Manufacturing Enginring, Univrsity of Calgary, Canada. 182

Tabl 1: Small Wind turbins airfoil in litratur Airfoil Airfoil Charactristics Blad Charactristics NACA Max thicknss Ratd powr 63-415 15% at 34.9% 20kW, dsign chord. Max wind spd cambr 2.2% at 10m/s, rotor 50% chord diamtr 10m, blad numbr 3. SD Max thicknss Ratd powr 7062 13.98% at 27.2% 600W, dsign chord. Max wind spd cambr 3.97% at 10m/s, rotor 39% chord diamtr 2m, blad numbr 3. SG Max thicknss Ratd powr 6043 10.02% at 32.1% 2kW, rotor chord. Max diamtr 3m, cambr 5.5% at blad numbr 3. 49.7% chord S 809 Max thicknss Ratd powr 21% at 38.3% 19.8kW, cut-in chord. Max wind spd 6m/s, cambr 1% at rotor diamtr 82.3% chord 10.06m, blad numbr 3. DU 96- Max thicknss Frquntly usd W-180 18% at 35.2% in combination chord. Max with othr cambr 2.5% at airfoils on larg 36.3% chord wind turbins. Rfrnc [13] [14] [15] [16] [17] RESULTS AND DISCUSSION Whn th airfoils in Tabl 1 wr inputtd into th XFLR5 and thir prformancs wr analysd basd on diffrnt critria such as thir cofficints of lift, cofficints of drag, pitching momnt cofficints and th most important, th lift to drag ratio, Fig. 1 rsults. Fig. 1: Graph of Glid ratio against angl of attack Ths rsults wr compard to th airfoils rspctiv data in litratur and a clos corrlation was obtaind, thus validating th application of th XFLR5. In ordr to crat a novl and mor fficint airfoil, thr airfoils (S1210, E214, and NACA 7409; s Tabl 2) widly considrd as som of th most fficint [18, 19], wr slctd and usd to crat a nw airfoil. In addition to thir arodynamic charactristics, airfoil E214 and NACA 7409 wr chosn for thir rlativ thicknss in ordr to mak th rsulting airfoil (OP 2-3) asy to manufactur. Tabl 4.2: Intrpolatd airfoils and thir charactristics Airfoil Charactristics By S1210 Max thicknss 12% at 21.51% Michal Slig chord. Max cambr 7.2% at 51.11% chord E214 Max thicknss 11.1% at 33.1% Richard Epplr chord. Max cambr 4.03% at 52% chord NACA 7409 Max thicknss 9% at 29.1% chord. Max cambr 7% at 39.5% chord NACA Morovr, thr ar two mthods of dsigning airfoils [20]. Ths includ using an invrs dsign cod (.g. Epplr cod) to prscrib flow paramtrs and com up with a dsird gomtry. Th scond mthod uss a trial and rror approach in combination with a numrical optimisation (itrativ) tchniqu/cod. Howvr, th mthod mployd for th cration nw airfoil in this study was to carry out an intrpolation btwn E214 and S1210 airfoils. Th rsultant airfoil was furthr intrpolatd with NACA 7409. Th outcom ld to th dvlopmnt of a nw airfoil dsignatd th OP 2-3 airfoil. This dsignation was just for th purpos of idntification. Th configuration of OP 2-3 airfoil is shown with Fig. 2 183

nsuring that it has th bst of all sids. Th Tabl 4 shows th s of th airfoil OP 2-3. Fig. 2: Th configuration of OP 2-3 airfoil Tabl 3 shows th charactristics for th rsulting airfoil whil Fig. 3 shows th glid ratio to angl of attack for th intrpolatd airfoils and th rsulting airfoil. Tabl 3: Charactristics of th nw airfoil (OP 2-3) Nam Charactristics Airfoil dsignation OP 2-3 Max Thicknss 10.17% of Chord Position of Max Thicknss 26.49% of Chord Max Cambr 6.26% of Chord Position of Max Cambr 45% of Chord Fig. 3: Glid Ratio of airfoil E214, NACA 7409, S1210, OP 2-3 Fig. 3 shows that airfoil E214 has th highst glid ratio. Howvr, it has its optimum angl for which th glid ratio is gratst at on angl point (7 ). Also from th graph, airfoil S1210 has a larg rang at which its glid ratio is high (abov 40 o from -1.5 to 10.5 ), although it dos not possss th highst glid ratio. Likwis airfoil NACA 7409 has a good rang though not as high as S1210. Comparing ths charactristics with that of th dvlopd airfoil, OP 2-3 shows that OP 2-3 airfoil has a good blnd of all thr. It has th scond highst glid ratio and th scond highst rang, thrby Tabl 4: OP 2-3 Airfoil Coordinats X Y X Y X Y 1 0 0.17538 0.08979 0.19789-0.00396 0.99298 0.00334 0.15523 0.08495 0.21988-0.00166 0.9804 0.00845 0.13608 0.07974 0.24274 0.00074 0.9642 0.01427 0.11798 0.07423 0.26641 0.00317 0.94524 0.02033 0.10099 0.06846 0.29086 0.00559 0.92414 0.02658 0.08515 0.06248 0.31602 0.00794 0.90128 0.03295 0.07052 0.05633 0.34186 0.01017 0.87699 0.03935 0.05715 0.05006 0.36832 0.01226 0.85151 0.04573 0.04512 0.04368 0.39535 0.01416 0.82504 0.052 0.03448 0.03727 0.42289 0.01591 0.79775 0.05811 0.02526 0.03095 0.4509 0.01762 0.76979 0.064 0.01747 0.0248 0.47932 0.01925 0.74131 0.06965 0.01111 0.01894 0.50807 0.02078 0.71242 0.07504 0.00627 0.01346 0.53711 0.02216 0.68323 0.08013 0.00285 0.00845 0.56636 0.02333 0.65385 0.08491 0.00069 0.00393 0.59575 0.02429 0.62437 0.08934-0.00007-0.00003 0.6252 0.025 0.59488 0.09342 0.00072-0.00341 0.65464 0.02543 0.56545 0.09711 0.00295-0.00629 0.68398 0.02558 0.53616 0.1004 0.00664-0.00861 0.71311 0.02542 0.50708 0.10326 0.0119-0.01029 0.74195 0.02495 0.47828 0.10567 0.01857-0.01161 0.77038 0.02415 0.44982 0.10762 0.02656-0.01271 0.79827 0.02302 0.42177 0.10909 0.03594-0.01343 0.82549 0.02158 0.39418 0.11006 0.04671-0.01376 0.85189 0.01983 0.36711 0.11041 0.0588-0.01376 0.87729 0.01777 0.34061 0.11005 0.07216-0.01347 0.90149 0.01544 0.31474 0.10896 0.08676-0.01288 0.92424 0.01285 0.28955 0.10718 0.10256-0.01201 0.94525 0.01004 0.26509 0.10477 0.11951-0.01088 0.96412 0.00704 0.24139 0.10177 0.13756-0.00951 0.9803 0.00397 0.21851 0.09824 0.15668-0.00791 0.99297 0.00119 0.19649 0.09423 0.17681-0.00606 1 0 Analysis of Rotor Paramtric Charactristics Basd on th nw airfoil, a SWT was dsignd with th charactristics shown in Tabl 5. Tabl 5: Wind Turbin Blad Charactristics Numbr of Blads Thr bladd Rotor Radius 1 mtr 184

Airfoil Typ OP 2-3 Approximat Tip Spd Ratio 6 Ratd Wind Spd 11m/s Cut In Wind Spd 3m/s Cut out Wind Spd 25m/s Typ of Wind flow Upwind Hub radius 0.1 mtrs A radius of 1.0 m and 3 numbr blads wr chosn so as to mak th wind turbin as compact as possibl. Th purpos of adapting th cratd airfoil to a wind turbin blad was to b abl to furthr th analysis and to ascrtain its applicability and fficincy. Fig 5: Blad Chord Distribution Th figurs show that an invrs rlationship xists btwn radial distanc from th cntr and twist angl as wll as with chord distribution. Using th chord distribution and blad twist from th MATLAB cods by Wood [12], a solid modl of th blad dsign was cratd as shown in Figs. 6 and 7. Chord Distribution and Twist Th chord distribution and twist of th blad wr dcidd using quations 6 and 7 rspctivly togthr with valus of 0 o for ovrall blad pitch angl and 0.1 m for radius of th hub. A MATLAB cod dvlopd by Wood [12] was mployd for th analyss. Th rsults of th analyss of th chord distribution and blad twist ar givn in Figs. 4 and 5 rspctivly. Fig. 6: Modl of Wind Blad Fig 4: Blad Twist Distribution Fig. 7: Th blad plan form and sction cuts CONCLUSION Th prliminary rsult showd that th novl airfoil OP 2-3 is mor fficint with bttr prformanc critria. Whn th arodynamic paramtrs of th airfoil, gnratd with AirfoilPrp_v2.02.01, wr mployd with WT_Prf, th outcom showd that th torqu, bnding momnt and optimum gnration incrasd with rotor rvolutions pr minut (rpm). Th maximum cofficint of powr (C p ) was 0.45 and th torqu varid btwn 6 Nm at 200 rpm and 26 Nm at 600 rpm. Th bnding momnts, at ths rotor spds, wr also btwn 11.5 and 35.0 Nm. Th wind spd that producd th maximum C p, torqu and bnding momnt rangd btwn 11.0 and 12.0 m/s. Th powr curv is shown with Fig. 8 185

[9] Miglior P, Orlmans S. Wind tunnl aroacoustic tsts of six airfoils for us on small wind turbins. National Rnwabl Enrgy Laboratory, 2003 [10] Tuhf Göçmn, Barıs Özrdm, Airfoil optimization for nois mission problm and arodynamic prformanc critrion on small scal wind turbins, Enrgy 46, 2012, pp. 62-71 [11] Manwll, J.F., McGowan, J.G. and Rogrs, A.L., Wind Enrgy Explaind: Thory, dsign and application, 2 nd dn., Unitd Kingdom, John Wily & Son Ltd, 2009 [12] Wood, D., Small Wind Turbins: Analysis, Dsign and Application, Springr, London, 2011 Fig 8: Graph of Powr Gnratd against Wind Spd (powr curv) REFERENCES [1] Ajayi, Olusyi O., Th Potntial for Wind Enrgy in Nigria, Wind Enginring, 34(3), 2010, pp. 303-312 [2] Ajayi, O.O., Fagbnl, R.O. and Katnd, J. Assssmnt of wind powr potntial and wind lctricity gnration using WECS of two sits in South Wst, Nigria, Intrnational Journal of Enrgy Scinc, 1 (2), 2011, pp. 78-92 [3] Ajayi, O.O. Fagbnl, R.O. and Katnd, J. Wind profil charactristics and conomtric analysis of wind powr gnration of a sit in Sokoto Stat, Nigria, Enrgy Scinc and Tchnology, 1 (2), 2011, pp. 54-66 [4] Ohijagbon O.D. Ajayi, Olusyi. O., Potntial and Economic viability of stand-alon hybrid systms for a rural community of Sokoto, North-Wst Nigria, Frontirs in Enrgy, 8 (2), 2014, pp. 145 159 [5] Jurczko M, Pawlak M, Mzyk A., Optimisation of wind turbin blads, Journal of Matrials Procssing Tchnology 167, 2005, pp. 463-471 [6] Xiongwi Liu, Lin Wang, Xinzi Tang, Optimizd linarization of chord and twist angl profils for fixd-pitch fixd-spd wind turbin blads, Rnwabl Enrgy 57, 2013, pp. 111-19 [7] Sdaghat, A. Mirhossini M., Arodynamic dsign of a 300 kw horizontal axis wind turbin for provinc of Smnan, Enrgy Convrsion and Managmnt 63, 2012, pp. 87-94 [8] Ronit K. Singh, M. Rafiuddin Ahmd, Mohammad Asid Zullah, Young-Ho L, Dsign of a low Rynolds numbr airfoil for small horizontal axis wind turbins, Rnwabl Enrgy 42, 2012, pp. 66-76 [13] Song, F., Ni, Y., & Tan, Z. Optimization dsign, modling and dynamic analysis for composit wind turbin blad. Procdia Enginring, 16, 2011, pp 369-375 [14] Wright, A.K., and Wood, D.H., Th Starting And Low Wind Spd Bhaviour Of A Small Horizontal Axis Wind Turbin, Journal of Wind Enginring and Industrial Arodynamics, 92, 2004, pp. 1265-1279 [15] Clifton-Smith, M. J., and Wood, D.H., Furthr Dual Purpos Evolutionary Optimization of Small Wind Turbin Blads, Journal of Physics: Confrnc Sris 75, 2007, 012017 [16] Chn X., Agarwal R. Optimization of FX, DU and NACA airfoils for wind turbin blads using a multi-objctiv gntic algorithm, Procdings of th 51st AIAA Arospac Scincs Mting, Grapvin, TX, 7-10 January 2013, AIAA Papr 2013-0782 [17] DUWIND, sction wind nrgy, Faculty CiTG,, availabl onlin [http://gcp.stanford.du/pdfs/nrgy_ workshops_04 _04/wind_van_rooij.pdf, Sptmbr 8, 2014], 2004 [18] Prasad Chougul, Sørn R.K. Nilsn. Simulation of flow ovr doubl-lmnt airfoil and wind tunnl tst for us in vrtical axis wind turbin, Journal of Physics: Confrnc Sris 524 (2014) 012009, doi:10.1088/1742-6596/524/1/012009, 1 10, 2014 [19] Prathamsh Dshpand and Xianchang Li. Numrical Study of Giromill-Typ Wind Turbins with Symmtrical and Non-symmtrical Airfoils, Europan Intrnational Journal of Scinc and Tchnology Vol. 2 No. 8, 195 208, 2013 [20] Martin Hpprl, Dsigning and Airfoil, availabl onlin [http://www.mh-arotools.d/airfoils/mthods.htm, accssd Dcmbr 19, 2014], 2007 186