Experimental evaluation of a flapping-wing aerodynamic model for MAV applications

Transcription

1 Exprimntal valuation of a flapping-wing arodynamic modl for MAV applications Jun-Song a, Da-Kwan Kim b, Jin-Young a, Ja-Hung Han a a Dpartmnt of Arospac Enginring, KAIS, 335 Gwahangno, Yusong-gu, Dajon, 35-7, Rpublic of Kora b COMS Systms Dpartmnt, Communication, Ocan & Mtorological Satllit Program Offic, Kora Arospac Rsarch Institut, Dajon, , Rpublic of Kora < Articl Info. > Publication itl Journal Hompag SPIE 5th Annual Symposium Smart Structurs and Matrials Publication Yar 8 Volum/Issu Vol.698, 698M Paginations DOI urthr Info. Rmark his PD fil is basd on th final submission to th publishr, and thr might b slight chang from th final form providd by th publishr. Copyright 8 Socity of Photo-Optical Instrumntation Enginrs.

2 Exprimntal valuation of a flapping-wing arodynamic modl for MAV applications Jun-Song a, Da-Kwan Kim b, Jin-Young a, Ja-Hung Han* a a Dpartmnt of Arospac Enginring, KAIS, 335 Gwahangno, Yusong-gu, Dajon, 35-7, Rpublic of Kora b COMS Systms Dpartmnt, Communication, Ocan & Mtorological Satllit Program Offic, Kora Arospac Rsarch Institut, Dajon, , Rpublic of Kora ABSRAC In th prliminary dsign phas of th bio-inspird flapping-wing MAV (micro air vhicl), it is ncssary to prdict th arodynamic forcs around th flapping-wing undr flapping-wing motion at cruising flight. In this study, th fficint quasi-stady flapping-wing arodynamic modl for MAV application is xplaind and it is xprimntally vrifid. h flapping-wing motion is dcoupld to th plunging and pitching motion, and th plunging-pitching motion gnrator with load cll assmbly is dvlopd. h compnsation of inrtial forcs from th masurd lift and thrust is studid to masur th pur arodynamic loads on th flapping-wing. Advancd ratio is introducd to valuat th unstadinss of th flow and to mak an application rang of flapping-wing arodynamic modl. Kywords: Bio-inspird, lapping-wing, Arodynamic modl, Micro air vhicl, Wind tunnl tsting, Advancd ratio. INRODUCION h dsign of wing structurs of flapping-wing vhicls is quit diffrnt from that in fixd- and rotary-wing aircraft. On of diffrncs is th us of arolastic dformation. or th convntional aircrafts arolastic phnomna hav bn rgardd as somthing to b avoidd or prvntd in gnral. Howvr, for birds and inscts, it is not always ncssary to rduc or supprss thos dformations bcaus thy indd us th arolastic charactristics of thir wing structurs. Actually most of birds and bats can chang thir wing shaps activly to gnrat propr arodynamic loads. Howvr, it sms that th passiv pitching causd by th intraction of flxibl wing structurs and arodynamic loads contributs a lot to th incras in arodynamic prformancs. h charactristics of flapping-wing arodynamics ar dpndnt upon th kinmatics of wing motion, wing gomtry, wing structural proprtis and flow condition. h flapping-wing arodynamics govrnd by unstady low Rynolds numbr flow has not bn fully undrstood; spcially th rols or ffcts of lading-dg vortx, span-wis flow, and dlayd stall nd to b furthr invstigatd. Currntly, many rsarchrs dmonstrat thir bio-inspird flapping-wing MAV by trial-and-rror approachs. ik a pigon or magpi, bird-scal natur s flyrs hav highr aspct ratio wing, lowr flapping frquncy and rlativly small wing dformation than inscts or hummingbirds. hos craturs xprinc th quasi-stady flow fild which is much mor prdictabl than unstady on. Daurir [] stablishd a flapping-wing arodynamic modl, calld modifid strip thory (MS). h arodynamic modl maks it possibl to stimat th arodynamic prformancs of bird-scal flapping-wing MAV in th phas of prliminary dsign and dvlopmnt. Kim [] improvd th MS to considr highr rsultant angl of attack, and addd th dynamic stall modl for not only pitching but also plunging motion. H obtaind th arodynamic paramtrs usd in MS from th stady stat wind tunnl tst data. Evn th flapping-wing arodynamic modl is vry fficint analyzing tool but it should b validatd by th rfind xprimntal data undr various kinmatical and arodynamic conditions. Howvr, thr ar not nough xprimntal rsults at low Rynolds numbr rgim and in th broadn rang of wing kinmatics paramtrs. Accordingly w dvlopd an xprimntal dvic to acquir th arodynamic data undr various flapping-wing motions at low Rynolds numbrs, and th xprimntal rsults wr compard with MS simulation rsults. jahunghan@kaist.ac.kr; phon ; fax ; Activ and Passiv Smart Structurs and Intgratd Systms 8, ditd by Mhdi Ahmadian Proc. of SPIE Vol. 698, 698M, (8) X/8/$8 doi:.7/ Proc. of SPIE Vol M-

3 . EXPERIMENA SE-UP AND MEHODS o analyz th arodynamic charactristics of th flapping-wing, w dcoupld th flapping-wing motion into two mainly ffctiv wing motions: plunging and pitching. Sunada t al. [3] dvlopd a plunging and pitching motion gnrator; howvr thy did th xprimnts in th watr tank at vry low actuation frquncy. Okamoto t al. [4] also trid to masur th arodynamic forcs and momnts around flat-plat wing undr unstady wing motions in th wind tunnl. But thos xprimntal dvics hav som limitations such as small amplituds (~.5c) and low actuation frquncy lvl (~Hz). Birds hav plunging amplituds mor than tims of thir wing chord lngth. lapping frquncy dpnds on th wing span but thy usually hav 3~7Hz for 6cm wing span (c.f. Magpi) [7]. Considring natur s flapping motions, w dvlopd rlativly larg amplitud (pak-to-pak 6cm) and high frquncy (~Hz) motion gnrator.. Plunging-pitching motion gnrator ig. shows th ovrall shap of th dvlopd plunging-pitching motion gnrator, consisting mainly of plunging motion gnrator, pitching motion gnrator and load cll assmbly. Basically th scotch-yok mchanism convrts th rotational motion of th motor into th sinusoidal motion, and th attachd balancd mass rducs th vibration of th ntir systm. h plunging frquncy incrass linarly with th spd of th plunging actuation motor and th spd is controlld by th xtrnal analog signal of invrtr. oad cll assmbly is attachd to th plunging motion gnrator as shown in ig.. It consists of two load clls (KOYO-65AQ-3, 5kgf) to gaug th lift and th thrust dirctional forcs, and connctd to two dynamic strain amplifirs (DN-AM3). his part is hidd in th aluminum fairing for th wind tunnl tsting. h pitching motion gnrator is mountd on th lift dirctional load cll. And it can b rplacd by thr typs of tst bd, () static tst jig to fix th angl of attack for stady stat wind tunnl tst of th tst wing and th plunging-only tst, () passiv tst jig to gnrat th passiv pitching motion by translational spring as shown in ig. and (3) activ tst jig to install th stpping motor for activ pitching control, rspctivly. In this papr, w usd th static tst jig to prform th stady stat wind tunnl tst and plunging motion only tst at fixd angl of attack as an initial study of this rsarch. W usd two long rang displacmnt lasr snsors (B-3/B-) to monitor th plunging and pitching wing motions. Bfor w installd th motion gnrator to th wind tunnl facility, w valuatd it by data whthr it gnrats propr motions of dsird amplituds and frquncis. Morovr, to find th rlationship btwn [gf] and [mv], ach dirctional load cll was calibratd by th wight of a balanc. his xprimntal dvic nds 5 A/D ports ( load clls-lift/thrust, lasr displacmnt snsors-plunging/pitching, acclromtr-plunging) and D/A ports (plunging frquncy and wind tunnl spd control). All th signals ar managd by RI (Ral-im-Intrfac) DSP board (dspace-ds3). h sampling tim is fixd to ms throughout th xprimnt. Pitching Motion Masurmnt Point Passiv Pitching Motion Gnrator ift c θ Scotch-yok Plunging Motion Gnrator oad cll Assmbly hrust U α h & Static st Jig g r Plunging Motion Masurmnt Point h Y Z X ig Plunging-pitching motion gnrator ig oad cll assmbly and th dirction of forcs Proc. of SPIE Vol M-

4 h low pass filtr with th cut-off frquncy of.5 tims of th plunging actuation frquncy was applid to th ntir snsor signals. h discrt ourir transform filtr was usd to prvnt th phas dlay.. Inrtial forc modling h load clls attachd to th plunging motion gnrator xprinc th acclration of plunging motion. Du to th mass of load cll itslf, w can obsrv th signal, but it can not b dtrmind thortically. o xtract th pur arodynamic loads from th combind signal of th inrtia and th arodynamic forcs, w introducd th dynamic calibration of th load cll to mak an inrtial modl. irst of all, w xamind th structural charactristics of our masurmnt systm by th modal tst (PCB86C, HP356xa). h first natural frquncy of th xprimntal dvic is gratr than Hz. h plunging motion actuation frquncy f is austd from i =Hz to Hz. Hnc, w mad sur that th chang of structural proprtis of load cll assmbly such as phas dlay, and quivalnt mass of load cll ar not varid with th frquncy. h raw data of ach load cll ar composd of = ( f = i ) ( f i ), I A ( f = i ) + ( f i ) I = A + = = () h subscript I and A imply inrtia and arodynamic forcs, and th suprscript and dnot lift and thrust, rspctivly. If thr is no pitching motion gnrator which is mountd on th lift dirctional load cll, w could introduc th quivalnt mass of load cll assmbly m and m to build an inrtial modl of ach dirction. ( ) = m a I, = m I a,, ( ) In cas th lift and th thrust dirctional acclrations ar known, w can dtrmin th quivalnt mass. m ( ) f i = = I, RMS a RMS, m ( ) f i = = I, RMS a RMS () (3) h lift dirctional acclration a is asily calculatd bcaus th plunging motion has th xact sinusoidal form. In contrast, th thrust dirctional acclration a can not b drivd simply. Hnc w mak th two dummy mass which hav th diffrnt wights ( m d =8.98g, m d =43.5g) and it can b assmbld on th lift dirctional load cll just lik th static tst jig in ig. Whn th dummy masss ar installd, thn th inrtia forcs can b xprssd as ( ) = ( m + m ) ( a ),, ( ) = ( m + m ) ( a ), I rom quations () and (4), w can gt th acclration componnts as follows: ( a ) ( f = i ) ( f i ) I, = I, =, ( a ) m I ( ) ( ) I, I, (4) = (5) m inally w avragd thos acclration valus to gt much prcis ons. Basd on th rsult of th quation (5), w can xprss thm to analytical forms. a f i = ( t) = h( πf ) sin(πft), a = i ( t) = C h( π f ) ( sin(πft) + ( + C )sin(π ( f ) t + π )) f (6) whr C =.889, C. for i = to 9. Proc. of SPIE Vol M-3

5 8 6 5 ift Dirctional Acclration [m/s ] h=.4m f=5hz a modl a modl a xp a xp hrust dirctional acclration [m/s ] Equivalnt Mass [g] 4 3 m q m q im [sc] ig 3 ift and thrust dirctional acclration modling Plunging rquncy [Hz] ig 4 Equivalnt mass of lift and thrust dirction h cofficints C and C rprsnt th structural coupling factor btwn th lift and th thrust. It is dtrmind by th curv fitting to minimiz th rror btwn th xprimnt data (5) and th acclration modl (6) for i = to 9. ig 3 rprsnts th rsult of th lift and th thrust dirctional acclrations modling at h =.4m and f =5Hz. rom th quation (3), th quivalnt masss of ach dirctional load cll can b valuatd as shown in ig 4. It is confirmd that th quivalnt masss ar not varid with th actuation frquncy, and that thy hav th man valus of m =3.389g and m =.887g with th standard dviation.5g and.33g, rspctivly. Adding th inrtial ffcts of static or passiv tst jig, w can calculat th total inrtial forcs. Evntually w can sparat th signal from th inrtia combind on to pur arodynamic loads. * ( ) = ( m + m + m ) a I tst w whr tst, static d = ( m I + mtst + mw ) a *, ( ) * m = m, m tst, dynamic = md, m w mw + m jo int = = 5.37g (7).3 Wind tunnl tsts of th plunging-pitching motion ig. 5 shows th xprimntal dvic assmbld to th low-spd wind tunnl facility in KAIS. h wind tunnl has 3 x 3cm squar and cm lngth tst sction, and th flow vlocity can b controlld from m/s to 5m/s. asr displacmnt snsor (Pitching) ow-spd Wind unnl st wing Anmomtr (Van yp) Wind unnl Control Panl Plunging Motion Gnrator Acclromtr Amp. (Vrtical) asr displacmnt snsor (Plunging) DAQ Systm (dspace Control board) Plunging Motion Controllr oad Cll Amplifir ig 5 Plunging-pitching motion gnrator installd in th low-spd wind tunnl Proc. of SPIE Vol M-4

6 o us our flapping-wing arodynamic modl, MS, w startd th wind tunnl tsting to gt th static lift and drag cofficints vrsus angl of attack of th tst wing that has th span b =8mm, chord lngth c =3mm, thicknss t =.5mm, aspct ratio AR =6 and mass m w =7.45g. It is mad of carbon/poxy fram and balsa to rsist th arodynamic forcs and it is sufficintly rigid in th rang of ~Hz xcitation frquncy. W simulatd our arodynamic modl at zro frquncy to gt th arodynamic paramtrs which hav th last rror compard with th xprimnt data of th stady stat wind tunnl tsting of th airfoil. hn using ths paramtrs, summarizd in Equation (8), w could stimat th arodynamic forcs inducd by dynamic plunging and pitching motion without furthr xprimnts. As shown in th ig 6, th angl of attack was austd from - dg to dg with dg incrmnts at th flow vlocitis U = 6 and 8m/s, R =4 and 65, rspctivly. η =.9, ( C ) uppr =.36, ( ) lowr C =.9, s d α =, ( stall ) max c C d =3.9, ( ) c d f α =8., ( stall ) min α =-8.8 (8). lat-plat wing AR=6 Cofficints of ift and Drag C, Exp., R=4 C, Exp., R=4 C, Exp., R=65 C, Exp., R=65 C, MS Simulation C, MS Simulation - - Angl of attack [dg] ig 6 ift and thrust cofficints at R=4 and R=65 with MS simulation rsults.4 lapping-wing arodynamic modl, MS Daurir [] proposd th flapping-wing arodynamic modl by using simpl strip thory. Mainly, this thory is volvd from th modification of th fluttr analysis for larg amplitud wing motion and low spd flow. Modifid strip thory has th svral assumptions: invariabl finit span, continuous sinusoidal wing motion, and low rsultant angl of attack. Various arodynamic ffcts, such as cambr ffct, partial lading dg suction ffct, viscous ffct, unstady wak ffct, and dynamic stall modl of pitching motion can b considrd in this modl. Kim [] improvd this arodynamic modl for th highr rsultant angl of attack, and applid th dynamic stall modl not only for th pitching but also plunging wing motion. his papr is focusd on th xprimntal vrification of our flapping-wing arodynamic modls ( MS is original vrsion [] and MS-stall is improvd on []). 3. RESUS AND DISCUSSION Using th xprimntal st-up and mthods dscribd in th prvious chaptr, now th xprimntal data and th simulation rsults ar analyzd. h xprimntal conditions in this papr ar flow spd U =6m/s, plunging amplitud h =.4m, plunging frquncy f =~9Hz (Hz inc.) and fixd angl of attack θ =, 4, and dg. Shown ig 7 is th tim history of plunging motion, angl of attack, and lift and thrust cofficints at fixd angl of attack of 4 dg and th plunging frquncy of 5Hz. MS-stall and xprimnt data ar vry clos but MS can not Proc. of SPIE Vol M-5

7 follow th valu nar th pak of lift cofficint. It addrsss that th dynamic stall modl and th stall critrion of MSstall ar bttr than thos of MS. h thrust cofficint of MS is diffrnt with that of xprimntal rsult and MS-stall. rom th stall critrion usd for MS, thr is a big discontinuity during th upstrok. It producs th signal having th twic frquncy, bcaus w applid th numrical filtr to mak th sam signal procssing condition as th xprimntal data..4 h [m] α [dg] Exp MS-stall MS C. C Exp MS-stall MS im [sc] ig 7 im history of plunging-only tst, U = 6m/s, θ = 4, f = 5Hz h ffctiv way to validat th arodynamic modl is to compar th man and RMS (Root Man Squar) valus of lift and thrust cofficints. h igs. 8 and 9 show that th MS-stall is bttr than MS with bttr comparison with th xprimntal data ovr 5Hz. Evn though thr is no pitching motion; th dynamic stall modl with MS-stall critrion calculats th accurat arodynamic loads around th tst wing. h rsultant angl of attack γ is calculatd from th wing kinmatical paramtrs []. So, th γ is incrasd with th incras in th plunging amplitud, plunging frquncy and fixd man angl of attack θ at fr stram vlocity U. (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS Man valus of lift and thrust cofficints.3. h =.33c θ = 4 dg R = Man valus of lift and thrust cofficints h =.33c θ = dg R = Plunging rquncy [Hz] Plunging frquncy [Hz] ig 8 Man lift and thrust cofficints h =.4m, θ =4 and, R =4 Proc. of SPIE Vol M-6

8 (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS (C, Exp. (C, MS-stall (C, MS RMS valus of lift and thrust cofficints h =.33c θ = 4 dg R = 4 RMS valus of lift and thrust cofficints h =.33c θ = dg R = Plunging rquncy [Hz] Plunging rquncy [Hz] ig 9 RMS lift and thrust cofficints h =.4m, θ =4 and, R =4 h xprimntal conditions of igs. 8 and 9 ar th sam xcpt th fixd man angl of attack θ. So, th fixd angl of attack dirctly affcts th stall critrion. or th cas θ =4 in ig 9, th RMS valu of lift cofficint of MS-stall starts to show discrpancy from th xprimntal data ovr th 6Hz. In addition th man thrust cofficints hav all ngativ valus; th plunging-only tst with fixd angl of attack could not mak th positiv man valu. h fixd angl of attack without pitching motion cass dirctly acclrats th stall phnomnon of tst wing. Howvr th wing of almost natur s flyrs is flxibl. It dforms passivly or activly thir pitching angl during th flapping motion to prvnt or dlay th stall phnomna. It is nough to us th MS-stall to calculat th arodynamic forcs of th birds at th cruising flight condition. Instad of monitoring th rsultant angl of attack, w introduc th advanc ratio J to judg th applicabl rang of MS. h MS is actually basd on th quasi-stady flow rgim; w can not apply it to th unstady rgion. h unstadinss of flapping-wing motion can b xprssd as a dimnsionlss paramtr, th advanc ratio J. It is originally dfind by th ratio of th flight spd to th spd of th wing tip for rotor blad. h smallr valu of J has largr unstadinss of th flow fild. In this rsarch, th advanc ratio is dfind as J = U h& U / hω. / = (C.5. (C θ = dg EXP MS-stall MS θ = 4dg EXP MS-stall MS θ =dg EXP MS-stall MS θ = dg EXP MS-stall MS θ = 4dg EXP MS-stall MS θ =dg EXP MS-stall MS (C ) rms (C ) rms Advanc Ratio J ig ( C, ( C ) rms, ( C and ( ) rms C Vs. Advanc Ratio J at Advanc Ratio J θ =, 4, Proc. of SPIE Vol M-7

9 h man and RMS valu of lift and thrust cofficints in igs 8 and 9 ar rprsntd again by changing th x-axis from frquncy to advanc ratio. W found that our xprimntal conditions blongd to th rgion of th quasi-stady flow. Howvr th advanc ratio is smallr, th xprimntal data of lift and thrust cofficints ar apparntly incrasd but th MS simulation rsults could not follow up. Du to th fixd angl of attack, it associats frquntly to th post-stall critrion and it contributs not only to nlarg th man lift cofficints but also to drop th man thrust cofficints. 4. CONCUSIONS W dvlopd th plunging-pitching motion gnrator to masur th arodynamic charactristics of unstady wing motions at low Rynolds numbr flow. h dynamic calibration mthod of load cll assmbly is introducd. Evn though th acclration information was not availabl, it was succssful to build th inrtial modl of ach dirctional load cll. h arodynamic loads xprimntally masurd ar compard with th simulation data of MS and MS-stall. h stall critrion using th highr rsultant angl of attack was xprimntally validatd in th rang of h =.4m, θ =, 4, dg, f = to 9Hz. inally w rplacd th frquncy to th advanc ratio to find th applicabl rang of our flappingwing arodynamic modl. W can stimat th arodynamic forcs around th flat-plat wing for th cas of th lift cofficints, J 5 and th thrust cofficints, J In th nar futur, w will prform th nxt stp xprimnts undr passiv and activ pitching motions. It will giv us th propr pitching motion to nhanc th charactristics of lift and thrust. Morovr, th applicabl rang of our flapping-wing arodynamic modl will b rvaluatd. ACKNOWEDGEMEN his work was supportd by th Kora Rsarch oundation Grant fundd by th Koran Govrnmnt (MOEHRD) (KR-7-33-D). h first thr authors would lik to thank th Brain Kora Projct in 7. REERENCES J. D. Daurir, An arodynamic modl for flapping-wing flight, Aronaut. J. 97(964), 5-3 (993). D.-K. Kim, J.-S., J.-Y. and J.-H. Han, An arolastic analysis of a flxibl flapping wing using modifid strip thory, SPIE Smart Structurs and Matrials & Nondstructiv Evaluation and Halth Monitoring, San Digo, CA, USA, Mar S. Sunada and A. Sakaguchi, Unstady forcs on a two-dimnsional wing in plunging and pitching motions, AIAA J. 39(7), 3-39 (). 4 M. Okamoto and A. Azuma, Exprimntal study on arodynamic charactristics of unstady wings at low Rynolds numbr, AIAA J. 43(), (5). 5 M. J. C. Smith, P. J. Wilkin and M. H. Williams, h advantags of an unstady panl mthod in modling th arodynamic forcs on rigid flapping wings, J. Exp. Biol. 99, (996). 6 S. A. Ansari, R. Żbikowski and K. Knowls, Arodynamic modling of insct-lik flapping flight for micro air vhicls, Prog. Arosp. Sci. 4, 9-7 (6). 7 A. J. Ward-Smith, Biophysical Arodynamics and th Natural Environmnt, 68-, John Wily & Sons, 984. Proc. of SPIE Vol M-8