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On the Motion of a Vortex Ring and a Vortex Pair : Have we had a centurial misunderstanding?: University of the Ryukyus Repository

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Title

On the Motion of a Vortex Ring and a Vortex Pair : Have we

had a centurial misunderstanding?

Author(s)

Nagai, Minoru; Ameku, Kazumasa

Citation

琉球大学工学部紀要(66): 1-5

Issue Date

2004-03

URL

http://hdl.handle.net/20.500.12000/1454

(2)

BulLFacultyofEngineering・Univ、oftheRyukyusNo、66,2004

OntheMotionofaVOrtexRingandaVOrtexPair*

-Havewehadacenturialmisunderstanding?-

MinoruNAGAI**andKazumasaAIVmKU**

FacultyofEngineering,UniversityoftheRyukyus

Nishihara,Okinawa903-O213,Japan

dFnagai@tcc・u-ryukyu・acwjp

Abstract・Tbexaminethcengmeeringapplicationofanartificialvortexring,theinducedvelocity

fleldaroundavortexrmghasbeenstudiedwiththepotentialflowtheory・Asresults,sincethe

inducedvelocitybecomeszerofarapartfiPomthevortexring,theringdoesnotmovebyitsown

inducedflowfield・Inothcrwords,avortexringdoesnotnecessarilymoveatthespeedasusuallyit

mighthavebeenmisundcrstood・

InthispapeBthefIowfieldinducedbyavortexringandthensupemnposingvariousstrength

unifbrmflowsonthefieldarecaIculatedanddiscussed・Thispaperalsoclearsthattwoparallel

slraightvortexlinesncighbormgtoeachotherdonotnecessarilyrotateorgoparallelwiththe

velocities,whichmayhavebeenmisunderstoodfbrIongtime.

Keywords:PotentialflowthemybVbrtexring,VOrtexpair,Inducedvelocity,Vbrtexmotion.

、02:lenglh丘omeachvortexlme R:mdiusofvorteming U:unifblmflowvelociw Ubn:criticalvelociW xbXz:Cartesiancoordinates XYIpositionofvortexpair zmD:cylindricalcoordinates

ZR:positionofvortco[ring

(GにeklctteTs) c:mdiusofaciIcularvortexco祀 り:strcamfimction r:cirmlation 入:=(好功)/(cZ?+功) 兀:mtioofthccimumfbImcc 1.nvTRODucnON OneoflheauthoIshaslccentlyinspiⅡ巴dmeusageofartificial

voltexnngfbrvariousfluidmachmeTydevices(1).Artificial

vorteKringmayseTveasanewwmdfmbrventilation、Whenit issctatmeoutletofadimseWorte9Kringmightimpmvethe di節sereHiciencyatconsiderHbにrate.

Befb”Uleapplicationoflheartificialvortexring,authors

邸ammcdlheinducCdflowfieldbyavortcxringwithUle

potentialflowlheoryThen,apmblemofthenecessalyfbTeto

fixthevoltcxlingtothespacewasmmedouLHowlaIgefbICe

wouldbeneededto5xlheringartificiallymtatingamundits

circumfbにntialvortexline?InotherwoIdsbifmevortexringis

notHxedtospacebmenngshallmovemewayjustasany

conventionaltextbookhastaughtusfbrlongtime. 2.THEORYANDDISCUSSION 21CaseofastationaIyvortexring

Inafluiddynamicstextbook,motionsoftwopamUelstmight

vortexlinesarealsodcscribedasiflheyaェ℃moved応Iativelyto

eachotheTatlhevelociwuniquelydecidedbytheir”lative

mcngthofvortices・m1hispap露aumors,calculationsand

discussionshavefbcussedthesebasicprOblemsofvortexnngs andvoltexpalms.

PotentialflowfieldamundaspacefixedvortexringisObtamed

asmEquation(1)andmFigu泥1.

v'一訂露梺`。

‐表oMpw-厚M

DL-Zハ川鼠-2沢…]'’

準鶉鋤ルーzハnW]',

(1) NOMENCLArURE

dZ2:minimum,maximumlenglhfomvoItexring

D:lengthhOmvortexnng E:secondcompleteeUipticintegral F:filstcomplctecllipticintegml

Figuにlshowsstr麺nlmesmlhecentmlplancmcludmgIhc

centlalflowaxis・Asseen節mEquationlandlhefigU鹿,the

qowvclocityfarapartmmlhevortexringbecomeszcm,sothat

*Received:June20,2003.PrCsentedatUle5lhJSMBKSME

FluidsEngineemlgConfbrenccOWagoya,2002-11)

**DeparhnemofMeChanicalSystemsEngineering

(3)

NAGAI・AMEKU:OntheMotionofaVortexRingandaVortexPair 2 enti定Howfieldisatl己sttothevorte9[1ing・II1olherwolds山e vortexringisfixedtoUlespace,evidentlybecausethe calculationhasbeenpracticedabout`hspacefixedvort甑Iing'1 lhisspeedas‘℃ritical,,、Itiscleaエcdthatifthesuperlmposmg unifbmlflowislargerlhanUlecriticalspeedlheouternowcan gothmughthemsideofthevmtexring・Ifthespeedisweek,

outerHowcannotgommUghmthelingandlhefluidaroundthe

。』,}/

、(Iiiiii).~〆fL.

~上←/1

;:

:!

「~ ̄い、、;

■(轍■↑、<■

0.151(

vortexringcannotgooutmmUlenearfield 0.1 m.i

do51

….…-,←.:.… 。、.I

罫輿、_

星 2 皇 1 0 0 0 麹〆 /: 。‐。。?$O・・・・ゲル・・・い・・・o・」・ 0.05:

/i

0.1 I 2 2-1o1 Z FiglStreamlineamundastationalyvortexling (R=1,1=1,U=O) 2 Z -2‐1o2 Z Fig、2S口已amlinesaJoundaslowb/movingvortexring (R=1,1=1,0=0.125) ThemducedflowspeedatlhecenterofUlengulCiscalculatedas fbUowmgEquation(2).Wemaycallthisspeedaslhecritical speed,bBcauseUlisspeedmaybecomcthekcyspeedmlhecase Whendlevortexringismoving”IativelytotheSpace. (CriticalSpeed)(2)

。-孟一ひ“

Inthcnonnalizedflowfield(R=1,吟1)inFigul巳1,thecritical speediscalculatedas0.5. 2 ~ 0 Z2Casesofseveralmovingvortexlings FigurB2showsthesupenmposingofaunifbnnflowonthe voTtcxringinducingflowindicatedinFig1rCl,andtheunifb[m flowstr己ngUlisonefburlhoflhecTiticalSpeedLe,0.125.WhiIe thefigul巳ishPacedonthecoordinatesfixedtomevorte,、ing,we canseethefigur巳asdleflowamundaslowlymovmgvortex ringlBlativeitolhespace,Inlhiscase,theflowaccompanied wiIhthevort甑ringischcuIatmgonlyinsideofasphericalarea, OnehastonoticethatitisnotsocalledHiU,ssphericalvortex flowbbecausemtheHill,svortexthevorticesarcunifbnnly distributedinthesphericalarBa. Z -2 ‐】 0 2 Fig3StIEamlinesamundavortexring movmgwiUlcriticalspeed (R=1,1=1,ひ=o,5) Figu照4isthehildcaseoflheflowwheTC1heunifbrmflow strBngUlistwiceofmecriticalspeed・Itisthecaseof値stmoving vortexTing応lativelytolheSpace,Asdescribed曲oveblheouter flowcangothmughlhemsideoflhevortexnng・Thefhmiliar flowflcldaroundlhecigalBttesmokelingmaycmcSpondto lhisfigu妃. Figurc3showssccondcaseofamovingvortexring,inwhich thesupenmposmgunifbrmHowstrmglhisexactlylhecritical・ nefigul巳isobservedbylhecooldinatesfixedtothevolte9mng lhatismovingatmecriticalspeedr巳lativelytolheSpaca EvidcnUybBowspeedatlheccnterofthefiguにbecomeszem, sincetheunifbrmnowandthevortexinducingflowaIc cancelledeachotheratUlecenteTbmUliscase,theouterflowcan nevergothJDughorpenetmteUleinnerfieIdofdlevortexring ThesupenmposmgunifbrmflowisIhesameSpeedbuthas opposiに。i応ctiontothemducedveloci坪Solhat,wemaycaIl ComparingFiguにs2,3and4,itiscleamedthatonlytherelative movlngspeedtolhecritical印eedWhichislhefimctionofthe ci1℃ulationandmeradiusoflhevorte9〔ring,decideslheflow fields. 「 …-0.8.1- -0.6 : --.-0.4-- --0.8…↑ ←=q-P ̄P ̄ --.-1.…_  ̄ げ一十⑭--0?

 ̄貢~~-=---

-寸OL_ 0。Ⅱ。 ---.-0-.雷一・,‐‐

(4)

BulLFacultyofEngineering,Univ・oftheRyukyusNo、66,2004 3

U-2☆-会一喝にiiucaIspeed)⑥

Z ~ 2

。!

、、、0

/0

~…7

× 州/ 」P ’〆 。〆 〆 if,』 デ ’ノノ》 〆 β 坤ノグ ウ ヴ ゴ ヰ〆〃} 1,i11.34.1……4..…‐..『 0 0 -1 2 -2-1o z2 Fig.4StlEamlinesaroundafiLstmovingvort甑【ing (R=1,1=1,吟1) -2-2-10l2 Z

Fig、5s甘CamlinesamundastationaIyvortexpair

(X=1,-1,1=1,ひ=O)

PmfbssorBahchelorShowedUlesamedIccflowfieldsinduced

byvortcxringsinhistextbook(2),howevablheywe『edescnbed

asthepossibilitiesoftheflowfield・Heindicatedlhatthe

di碇冗nccsoftheflowpattemmnonglheseHgu”s8reonly

comefomUleChamcterofvortexringsnotcomemm血eoutcr

nowsh巳、9.1.HealsotaughtUlatmeouternuidcouldgo

lhroughthemsideofvolte9【ringonb/whmthemtioofstrengUl

ofvoIteo【E1amenttoringladiusissmallerU1anacriticalvalue、

TheOIcticaUybheanalyzcdselfinducedmovingspeedofavolteo【

Imgappmximateb/aslhefbUowingEquaUon9),whereemeans

lhesmallmdiusoflhe``tubevortices,,.

U一念鰯(÷ノ

(4)

Acmally,BatChelorandanyolherpmfbssorsdidnotdiscusslhe

瓢penmposmgunifbrmnowsonavorte9mingmducingnow

field,solhatbdleyseemnottoaccepMhemolionofvolt邸ring

wilharbimlyvelociWmhefluid5Uedspaceatl巳sL

Furthem1ore,ithasbeenundcrBtoodfbrIongtimeU】atdlespeed

ofselfmovingvorte9mngcouldnotcalculated,otherwisebc

infinite,becauseoflhemaUlematicalsingularibノofIhering

519ment 2.4Casesofsevelalmovingvorte0[pahs

Figul巳6showsnowneldamundaslowlymovingvortexpahblt

isaspecialcaseofUleflowwhendlcmperimposedunifbnn

flowspeedisonefburlhofdlecriticalSpeed・Inlhiscase,dle

nowaccompaniedwilhlhevorteo(pairiscilpulatingonMna

nearchcularcylindricalzone、OnemightcaUitachCUlar

cylindricalvort邸nowlikeasHill,svortexsphe妃.

2 × 1 -1 2.3Casesofastationalyvolteo【pa1r

Equanon(5)andFigure5describelheflowficIdinducedbya

vorteoKpa1rbapairofpamUel副mightvortexlinesSincetheflow

vclociWElr8parttheorigmbecomeszemandthevoItexnngis

fixcdtolhespaceblhevortexpajrdoesnotmovcldativeb/tothe

Spacc、IndliscaSc,lhecTiticalouterunifbrmflowisobminedas

mEquation(6).

妙--釜'w笏汁圭如吃ノ

(5) 2 -2-1・01

Z2

Fig.6s賑amlinesamundaslowlymovmgvorteo[pair

(X=1,-1,Jと1,U=UbrWVノ

Figul己7showsUlecriticalflowfield8mundamovmgvorte9【

painTheouterunifbnnnowandlhevortexinducingnowis

cancelledeachotheratlhecentemfthefiguに.Ifd1eouterflow

stJmgUlorlhemovmgspeedofthevort甑pairisequalorundeT

1hecriticalspeed,theouternownevergoeslhmughlhefield

areabetweenlhevort甑Iines.

‐‐圭鰄(芸I

耽小mxハ(>]'ノ,]'’

(5)

NAGAI・AMEKU:OntheMotionofaVortexRingandaVortexPair 4

InJapanesetextbook,ProfbssorTatsuminfbrexampleshowcd

U】esamestrBamlinesofFigurB6whα】avortexpa1rmovesatdlc speedofonefburlhofUleauthorscoldcriticalspeed,because

lhatisIhemduccdspecdusuallyunderstood,Tntsumisaidthat

Ulefigur己isobsewedbythecoordinatefixedtothevorte9(par justlikeasPrandtltoldThatis甘ueinUlecaseofslowlymovmg

voItexpairs,howevaiiflhecaseofstationaIyvortexpairs,lhe

flowfieldbecomestothat8sinFigu定S1tmightbedeclamed

matthesetwoorfburfigul巳sareenti妃1ydiHbTmtflowfieldsto

eachothe凪 × 1 3.DISCUSSIONandCONCLUSSION Itisclea配dlhatanyvolte9(ringsoranyvortem(pahBdonot

necessaエilymovebyIheirownmducmgflowfie1.s,andlhat,d1e

flowpattemisdecidedbylheldativestrengUlsofouterunifblm

nowandvortices,inotherwords,宛lativemovingspeedof

voTtexrings/Pahstod1ecriticalspecd・Sofanalmostall

textbooksoffluiddynamicshavedescribedasifvort。(Iingsand

voltexpairsshouldmoveatafixedspeedbyUlcirownselfor

mumalmducingflowfields. -1 ・2 Z 0 -1 -2 Z

Fig.7Str巳amlinesarcundavortexpair

movingwidlcriticalspeed (X=1,-1,Jと1,ひ=〔ん減ノ

TIleaumo盃doacceptU1epossibnityofmovementsofavoltex

nngmdpahHowcv甑1heydonotagrBelheconceptU1ateveTy

vortexIingandpairShouldmoveato町onefixcdvelociWasso

farunderstood・TheTBmighthavebeenacrucialmi副md幹

standingonfluiddynamicsduringacenturialage、Oneoflhe

reasonsofmisunderstandingmaycomemmasimpleconfhsmg

abouMherdativeObservationsystemsofnowamundamovmg

bodyForthepmof;itiseasytosaylhatusuallywecan

undeIstanddledi碇冗nceofflowfieldsbetweenastationaJy

double‘i、e、,sourCbandsink,andamovingdoubletWhiCh

becomesaflowaroundamovingcimularcylindricalbody.

2 一

一・・…・…・・・

--1 ̄ × -0.8 --0.6 -0.4 =-0.2 -0.1 --0 -.0.1 1 0

[jEL墓二三

-1

ThcotherにasonofmisunderstBndingmi8htcomc廿0m⑪e

mathematicalsingulariticsofvoltexfilaments・Itmaybesaid

matsupenmposingofanyflowsjustonlyonapointof

singularityismcanmgless,becauselhesingulaJitydoesnotbe

affbctedbyUlesupenmposition・Solhat,calculatedwell-known

innnitivespeedofvortexlingfilamentandlheonefblmhof

criticalspeedinlhecaseofvmtexpairfilamentsmaybejudged

simultaneouslytobemeaningless. -2

zZ

 ̄Z ̄101

Fig.8stェcamlinesamunda値stmovingvortexpa1r

α=11~1,1=1,U=ZUia"ノ

Fi創施8showsanolherspecialcaseoflheflowwhenlheouter

unifblmnowhaslhestlCnglhtwiceUlecriticalSpeedlnUliS

case,theomerflowcangolhroughmemnerm巳abetwcentwo

vmtexlineswiUlthccenterSpeedjustsameasmecriticalsPeed

butoppositeflowdiにction.Obviouslyb1hisisdlecaseofafilst

movingvolteKparimhefIuidfiUedspaceatlpst.

Aquestionmaybeleft,saybmamass-IikcprObIemofvortex

nngandvortexlines、niactualphysicalpmblems,tomadoesor

q/phoonsfbrexample,twovorticesmaybemtelactedbyeaCh

othenandusuallylheweekvortexshallbeinfluencedmuch

mol巳thanlhesmngvortices・HoweveEhowcouldwedccide

Ulemassofvolte9(ringfi1amentorlinefilaments?Zemmassand

mfinitiveSpeedisthusUlemathematicalsingularity・AnyvoTte9[

doesnotbeaflbctedbyanysupeIpositionandmaymoveatany

arbimIyspeeddecidedbylheotherphysicalboundariesor

initialconditions・T11eflowpattemsofFigmc1toFigUrB8aI℃

concludedasUledi匪祀ntcasesofastationaIyand/ormovlng

vort甑nngandavoTtcxpainAnyvortexnngsandpairsshould

ProfbssorPrandtlseemedtohaveanotherunders位ndmg曲out

lheseHows・Inhistextbookp),Prandtltoldlhatthedi歴Imce

betweenFigu応sandFigu虚6onbcameECmlhedi錠rcnceof

Obscwationsystemsandsomattwonowsw巳rp1hesame・Hc

seemstohavcsamcmmmderstfmdingwilhBatcheloEThey

mighthaveaconvictiomhatanyvortexringsandanyvoltc9K

pairsshouldmovebytheirowninducingflowfields.

(6)

BulLFacultyofEngineering,Univ・oftheRyukyusNo、66,2004 5

notnecessariIymoveatthefixedspeedlhatmightbe

misunde応toodfbrlongtime. authorsattheirtimeofCaIifbmialnStituteofTbchnologybhas scntauthorsmirlypositivecommen侭.Hesaid`UnIessl己alfluid effectsarcincludedanddueconsideranonisgiventothefbICes lEquiredtomove(orkecpstationaIy)thevoltices,aUsoIutions a1℃possible、TT1elCqui1℃dfb1℃esmayormaynotbefbasibleto aPply,,. FinallybitmustbenoticedonceagainthaMheabovecalculations anddiscussionsarcrEstrictedtotheinviscidsteadypotentiaI flowtheoIics・IteDKcludesU1eefIbctofviscositiesofactualnuid, norUlegenemtion,st2bUityanddecayprocessesofaphysical voIt欧ringorpamAslhemattcroff嵐ct,PIcfbssorBachelor discussedthestdDiliwofalammarvoTtexIingandstudiedthe vortexringgenemtioninthewakesbehindblufrbodiesatla【ge

Reynoldsnumberc).Then,heconcludedd1epossibilitiesofIhe

stablelammarvoItexringsasdescIibedmrBgammgFigul巳s2,3 and40ntheotherhand,ourdiscussionsandthefindmgsaIBm thepuldymviscidmathematicalpmbIemsoflheidealnow fieldsbutwilhsinguIaJitiesofvoltexHlaments. PmfbssorA1iOgUt,atRochesterlnstimteofTbchnologyandthe

ChiefOIganizerofthe41hASR胆』JSMEJomtFluidEngineeTing

Confbrence,planedandcaIIedfbrcollabomtionswithaulhorson apanclconcemingthemovingvorticesmtheConfbrencc、 Howeventheplanbasbcenpostponedtolhcnextchanceofthe Confbrence. Autho応expresstheirsincereapp1℃ciationstoalldiscusselBof Iheseacademicfieldsofnuiddynamicsandhopetohaveanother chancctodiscussomheprObleminnearfnturc. SincethetopicsmightbeconcemedwidlacmciayccnturiaI misunderstandingonfluiddynamics,aulho応hopefhlly”quest soonerinspectionofthealticleandlhenrevisionsoftextbooks andtheothewortcxconnectingpapeTsonnuiddbmamics. REFERENCES [1]Nagai,M、,VbrtexRmg,JapanPatentAppliedNo2001‐ 125003,20014(InJapanesc). [2]Bachelo囚G、K,AnlnhuductiontoFluidDynamics, CambridgeUniv,囲已ssb19674,525. [3]PrZmdtl,L、,Fi1hrerdu1℃hdieSUtmungslehne,Friedlb Vicwcg&Sohn,1141,72. M]Tntsumi,正,FluidDynamics,Baifh-kan,1,82斗,119(In Japanese) [5]BachelonGK.,Aproposalconceminglaminarwakcsbehind blufrbodiesatlalgeReynoldsnumbeTblFluidMeCh、1956, 388-398. [6】SharifTICandLeonardA,VbrtexRings,AnnualRevicwsof FluidMechanics,24(1992),235-279.

[7]LimmandNickclsTB.,VbrtexRings,FluidVbrtjces,ed、

GrcenSL,1995,95-153. ACKNOWREDGEMENT ProfbssorM.InoueandPmfbssorEmeritusYSenoo,Kyushu University,kindlydiscussedwimauUlo鱈onlhesesomewhat confUsmgbutimportantagqユdaandgaveUlemmuchusefUl adviscs・OtherJapaneseprofbssoIsinJSMEandmheSoci幻of FluidMech8nicscouldnotundelsmdlheautholB,pomtsof findmgsandgavelhemlhefiBirlyncgativecommcntsProfbssor Max、PlatzeqNavalPostgmduateSchool,hasslmwcdmuch inte配standadvisedaulhorsmol己pmdentinspcctiontolhe

findmgsinhoducinganarticleonVbrtexRings⑥mdabookof

Fluid1brticcsm・PlatzeralsoinmducedcommentsofPmfbssor

SalpkayaatlhesamesChool,ahhoughlhosewelBnotappmval

wilhaumors,FinaIlMDnG、Y8tes,acoUeagueofoneoflhe

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