torr ~tirru 'V Q Hz N/m 2 EQUIPMENT z a r 1 INTRODUCTION

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1 8 ~tiu ilf'@m W@~(Q) H~W t N-J ERMEER Delft Univesity f Technlgy, The Nethelands a~ SYNOPSS As a cntinuatin f ealie wk, velcities have been easued in the nea wake f a del t in the wind tunnel By using slanted wie ht wie pbes, the axial and tangential velcity cpnents can be easued n the data eductin schee, the finite blade length and the blade tatin ae incpated F the btained lcal ciculatin and velcities, a C - a plt is cnstucted Althugh the data eductin has nt yet been fully elabated, cpaisn with a easued 2-diensinal cuve, at epesentative Reynlds nubes, shws easnable ageeent in the lw angle aea, and at high angles f attack, the expected stall delay is cnfied the ht wie pbe, the calculated ciculatin is pptinal t the peak-peak value f the fluctuatin NOTATON c blade chd C 9 lift cefficient: - 1-2~p c vltage f ht wie bidge speed f evlutins lift fce: p adial cdinate t adius distance vect influence atix velcity vect velcity axial cdinate angle f attack ciculatin pitch angle A d OR up spee ati: p ai density inflw angle aziuth angle tatinal speed: E f R s T z a cp ' Q Hz N/ /s /s 2 EQUPMENT 21 Wind tunnen 2/s kg/ 3 2~{ As an extensin f this eseach, a change has been ade f css wies t slanted wies, in de t easue velcity cpnents, athe than esultants Als, the finite blade length and the tatin f the blades ae incpated in the data eductin schee The easued lcal velcities ae used t ake an estiate f the lcal inflw t the blade With the ciculatin and the lcal inflw, the lift cefficient and the angle f attack ae calculated ad/s 1 NTRODUCTON n de t get a bette undestanding f the pefance f wind tubine blades, an attept is ade t quantify the lift cefficient n the tating blades f a wind tunnel del n pevius publicatins (1) and (2), it has been shwn that a easue f the bund ciculatin n the blade can be deteined f the velcity fluctuatin induced by the blade passage and easued at a fixed psitin in the nea wake Assuing that this velcity fluctuatin is induced by an infinite vtex line, epesenting the blade, ving paallel alng The easueents have been pefed in the pen jet wind tunnel f the nstitute f Wind Enegy This tunnel cnsists f a flw channel f cicula css sectin (diaete 224 ), with a fan at the inlet, a flw staightene and gauzes, see Figue 1 The flw staightene is ade f thin walled aluiniu, with a hexagnal hneycb stuctue Thee ae th~e identical gauzes: ne just afte the flw staightene and tw at a utual distance f 2 appxiately 2 befe the utlet The axiu velcity is 145 /s The degee f tubulence is 8 pe cent and the axiu deviatin f the aveage velcity is 16 pe cent The nn- unifity is adially distibuted, s the "peatinal tubulence" is less then 5 pe cent (at A= 6) This peatinal tubulence is a e epesentative quantity because a velcity deviatin ve the utlet aea ay be static, but is "felt" as a fluctuatin by a tating blade S the velcity deviatin is ade nn-diensinal with tatinal speed athe than with tunnel velcity 117

2 axis and blade chd n this way, it is pssible t deteine the axial and tangential velcity cpnents 22 Mdel The del has been specially designed f aedynaic easueents in the wind tunnel, see Figue 2 n the eseach, the ephasis is put n the t, which ust theef be well-defined and suitable t pduce data f veificatin f nueical siulatin pgas The aefil f the blades is nt a cn HA WT blade sectin, but it was chsen because f the availability f wind tunnel data ve a wide Reynlds nube ange The blades ae anufactued n a nueical illing achine t btain the highest feasible f accuacy Specificatins f the del: Radius 6 Nube f blades 2 Aefil sectin NACA 12 Rt cutut 3 pe cent Chd 8 Blade length 42 Blade twist 9<?) = (6 + 9tip) 'R, f 3 ::; 'R ::; 9 Replaceable tip 6, n twist The t is placed n an extended tube leaving 75 fee space behind the t plane The pbe psitin is set by a tavesing syste n adial diectin, this can be dne by cpute, with an abslute e f 2 n axial diectin, the adjustent is dne by hand; the abslute e is 2 (the exact psitin f the t plane is difficult t detect!), but with an inceental e f nly 2 A data acquisitin syste, cntaining a high-speed vltete, a ultiplexe and a cunte, is used t easue and ste the signals f the ht wies and the aziuth cunte The axiu saple fequency f the vltete is loo khz, this is enugh t keep tack f the 72 saples pe evlutin f bth wies atf= 16Hz Specificatins f the test ig: Hub height 233 (= tunnel axis height) Pitch angle adjustable within 1 Axial fce ete 5 N, between hub and fist beaing, signal tansissin by slipings Tque ete 1 N Aziuth cunte 1 and 72 pulses/evlutin Mt/geneat 15 kw, 4 quadant peatin, speed f evlutins adjustable t 16Hz 3 MEASUREMJEN'fS 31 Cnfiguatins and cnditins F the detailed velcity easueents, five diffeent cnfiguatins have been cnsideed: at A= 8: 9tip = 4, 2 and ; at A= 6: 9tip = 2 and Duing all the easueents the speed f evlutins was kept cnstant atf= 1165 Hz, the tunnel velcity was adjusted, t "" 55 and 73 /s, t atch the tip speed ati f espectively A= 8 and 6 n this way the Reynlds nube at the tip is kept cnstant (Re= 24 ) f cpaisn n each f the five cnfiguatins, adial taveses with the ht wie pbe have been ade at 4 axial psitins: R = 53, 7, 13 and 137 The taveses wee ade f 'R =4 t 'R = 11 with inceents f 1, and additinal statins at 'R = 95 and Data acqlllisitillil 23 nsftuentin The undistubed tunnel wind velcity is easued with a Pitt tube cnnected t a Betz anete The Pi tt tube is placed at a psitin epesenting the aveage velcity ve the utlet aea The velcities in the nea wake ae easued with cnstant tepeatue ht wie equipent The slanted wie pbe is calibated using the s-called effective angle appach (3) n this ethd, the velcity in King' s law: E2 = + B", S wntten f" :2 "2 k22 as an e 1ect1ve ve c1ty: eff = v nnn + pa, ia whee nnn is the cpnent nal t the wie and pa is the cpnent paallel t the wie The k-fact is a easue f the diectinal sensitivity f the wie with espect t paallel cling n a velcity calibatin, the cefficients B and n ae deteined n an angle calibatin, the effective angle is deteined This is the angle between the flw and the wies, which is a e iptant ppety than the angle between the t axis and the pbe hlde Because f tepeatue changes in the labaty venight, the calibatins have been dne befe evey easueent sessin Duing the easueents, the pbe ientatin is set with the plane f the wies paallel t the plane set by t 118 F each statin in the taveses velcity saples wee taken ~ f bth wies evy 5 aziuth angle f the blades ve 5 successive evlutins n Figue 3, a typical plt is given f the axial and tangential velcity distibutin ve 1 evlutin (72 pints), aveaged pe aziuth angle ve the 5 evlutins The blade passages can clealy be distinguished at 9 and 27 by the deteinistic fluctuatins; the stchastic fluctuatins aund 14 and 32 ae caused by the tailing vtex sheet ll DA1'A irediuc1'on n (2), an estiate f the lcal ciculatin was calculated f the peak-peak value f the velcity fluctuatin 1 assciated with the passage f a blade n the atheatical siulatin, the Bit-Savat law was used:

3 n a 2-diensinal situatin, with a ptential vtex in a paallel flw, the velcity is: v = v+ sxd 2 27tl si With a sens ving n a staight line alng the vtex, it can be deived that the peak-peak value f the bseved velcity fluctuatin is pptinal t the vtex stength and invesely pptinal with the shtest distance between vtex and sens: ~ = The ciculatin and lcal velcity can nw be calculated by ~~ J 1 [ n+l 21t isin l n a 3-diensinal situatin, with a staight infinite v- tex line f cnstant stength, the sae esult is btained as in the 2-diensinal situatin This appach has been used in (2), but, althugh easnable esults wee btained, it lacks the input f the finite blade length and the tatin f the blades These ppeties have been added in the extended data eductin schee 41 suing the eains cnstant in the aziuth ange This set can be witten in atix f: ~ C alcu l~in f the ciculatin The velcity vect at a single psitin (, z, '') in the wake can be witten as: (, Z, \jf) = O +- ip 41t () s X d Exainatin f the del es, by cpaing the easued velcities with the calculated velcities using the 3 s t When the blade is divided int n pats, the ttal BitSavat integal can be split up int n pats: v(,z, \jf) = v + + _l_ 41t [ l s X d s X3 d + + n s X3 d S 2 S As a fist attept, 7 axial velcities have been taken at diffeent aziuthal psitins, but at a fixed adial psitin, t calculate 6 adial 's nveting T, shwed that this atix is vey bad cnditined Nt vey supisingly, because the 2-diensinal appach using ~ aleady shwed easnable esults The velcity fluctuatin cntains the st infatin abut the ciculatin at the sae adial lcatin as the ht wie pbe; in deviatins give infatin abut the ciculatin distibutin n the est f the blade S, it is bette t use e adial statins and e aziuthal saples Because f the availability f velcity saples, it is easy t cnstuct an ve-deteined set f equatins and slve this using the least squae ethd l S Assuing n is cnstant ve pat i, they can be taken utside f the integals, which eain nly dependent n, z and '' The integals can nw analytically be calculated, esulting in a suatin f bth the axial and the tangential velcity: n del' w - T [:J shwed that with the tangential ve- lcities bette esults can be pduced, than with the axial velcities Finally, with the abve tw cnsideatins in ind, a highly ve-deteined set f equatins has been used t calculate the ciculatin in each f the 5 cnfiguatins: a ttal f 78 tangential velcity saples have been used f 6 adial statins (f 'R =4 t 9), with 13 aziuthal psitins each (f '' =4 befe t 2 afte the blade passage), t calculate the 6,ang's and the 6 s at the sae adial statins as the easueents have been pefed 42 Calculatin f the angle f attack ax (, z, '') = ax + 'L,Cax,in i= l n ang (, z, '') =,tang + L,Cang,in i= l F this, it can be seen that bth the axial and tangential velcity signal cntain the sae infatin abut the ciculatin dist1ibutin, nly the cefficients in the suatins ae diffeent T calculate then 's and a, a iniu f n+ 1 velcity easueents ae needed An bvius chice wuld be t take n+ 1 aziuthal velcities at ne adial statin, as- As easy as the definitin f the angle f attack is in a 2-diensinal paallel flw, s difficult it is in a 3-diensinal tating situatin: the path f the blade sectin is cuved and, as shwn in Figue 3, the velcity is highly fluctuating in bth agnitude and diectin Within the scpe f this pape, nt a theetical slutin has sught, but a pactical ne: the easued axial and tangential velcities have been used t ake an estiate f the inflw angle: <p = ac tan ( ax ) O -,tang S, the angle f attack is given by a= <p- 8('/R) 119

4 6 CONCLUSONS 43 Calculatin f the lift cefficient F the calculatin f the lift cefficient, the sae pble ccus as f the angle f attack: in a 3-diensinal situatin, thee is nt a ppe definitin This is 'slved' by just taking the 2-diensinal ne Substituting the definitin f the lift fce in the definitin f C1, the fllwing is btained: 2 c,=-p;nc in which ;nc epesents the incing velcity, given by: --/ (O-,tang) 2 + (={ 5 RESULTS The final esults ae shwn in Figue 4, tgethe with 2-diensinal NACA 12 easueents (4) The Reynlds nubes f 1 and 2 ae epesentative f espectively 4 and 8 pe cent f the adius n FigueS, the sae esults ae shwn with atching es The plt shws that in the egin f s t 1 angle f attack, the ageeent with 2-d lift data is encuaging n this angle f attack ange, the 2-d lwe suface bunday laye is cpletely laina On the uppe suface a Jaina sepaatin bubble gadually ves fwad with inceasing angle f attack Belw s, the 2-d flw is dinated by laina sepaatin f the bunday laye n bth uppe and lwe suface At elatively sall angles, eattachent f the bunday laye even passes the tailing edge, esulting in a athe cplicated flw situatin n this egin with elatively lage aeas f sepaated flw, the bunday laye will be vey sensitive t influences f tatin The plt shws highe calculated lifts, which ight be caused by tansptatin f bunday laye ateial in adial diectin Stall f NACA 12 at lw Reynlds nubes is caused by busting f the laina sepaatin bubble n the aefil nse Calculated esults f the t egin indicate stall delay, which ight be due t the fact that this busting des nt ccu in the tating situatin At 9 pecent adius, the pesence f the fee tip vtex will have its influence n the easued velcities Since the tip vtex is nt included in the data eductin schee, the calculatin esults will thus be stngly influenced in this egin 12 With the cuent easueent ethd and data eductin schee, easnable esults can be btained f the 1- a cuve f a tating wind tubine blade c The change in equipent f css wies t slanted wies has been successful with espect t the deteinatin f the axialand tangential velcity cpnents in the nea wake The extended data eductin schee incpating fite blade length and blade tatin, has nt yet been fully elabated, but lks pising At high angles f attack, appeaing in the t aea at high blade lads, the appeaance f stall delay is ecnfied Additinal flw visualizatin in the tating situatin is?esable t eveal the flw cnditins f the bunday laye de t bette undestand the cause f the stall delay ACKNOWLEDGEMENTS wuld like t thank Sin Tet f his assistance duing the ~sueents, Wi Biebs f his help in the data pc~ssg and pf Jan B Dagt f his suggestins and suppt the data eductin REFERENCES (1) ERMEER, N-J, AN BUSSEL, GJW, elcity easueents in the nea wake f a del t and cpaisn with theetical esults, Fifteenth Eupean Rtcaft Fu, Asteda, The Nethelands, 1989, pape n 2 (2) ERMEER, N-J, AN BUSSEL, GJW, elcity easueents in the nea wake f a del t and cpaisn with theetical esults, ECWEC Pceedings, Madid, Spain, 199, (3) BROEKHOEN, MJW, (in Dutch) The calibatin f slanted ht wies using the effective angle appach, Meandu W-9147M, nstitute f Wind Enegy, Delft Univesity f Technlgy, The Nethelands, 1991 (4~ Unpublished NACA 12 easueents, Lw Speed Wd Tunnel Labaty, Faculty f Aespace Engineeing ' Delft Univesity f Technlgy, The Nethelands, 1979

5 16 ;=====,---T, ----,---, - /R= /R=5 _ ----v c /R=6 "- /R=7 12 v /R = j x-/r=9 Re = 1<> ~f- t: -Re=2'"1 6! ""Lil i J M 2 Fig 1 The pen jet wind tunnel Fig Angle f attack () Lift cefficient vesus angle f attack / - -, <~ \ - ; ~ Fig 2 The test ig and t del ~~~~~~~~~~~~~ Angle f attack(') Fig 5 E gaph Fig 3 Aziuth angle (') Aziuthal velcity 121