Waka, Ryoji

Yoshino, Fumio

Tottori University Research Result Repository

翠翫「■23ヾThe lnfluence of the Side―Wall on the Flow around the?????，???Circular Cylinder with Tangential lniectiOn Of AirbyFu■lio YosHINO*and Ryoti VAKA*(Received October 20,1975)ThO experiinental investigation has been carried out tO inquire into thecause of the three_dimensionality Of the fIOw around the circular cyユind rwith tangential intectiOn Of air. It was found by means Of the oiユfーlo  neトhod that a strong vortex is shed from the surface of the cylinder near aside_wall and that seems to be the cause of the three…dimensiOnality.l lntЮductio■Ve have carried out the experiment about the flow arollnd a circular cylinder withtangential injection of air for some years, and many knotty problems resulted fromthe experiinentl)。 SOme of them were those of the influence of R夕, θデ and Cμonthe transition of boundary layers of the external flow, the influence of 買ヮ andス買on the relation of CPぅ toθυsP,the structure of the slot, induced drag at the centerof span and so on.However we took the most interest in the existence of the induced drag even atthe center of the span, because, in he experilnent of this kind,the flow around thecylinder is in general regarded as two―dilnensional,  Then we carried out the expe‐rilnent2)tO require into the cause for this induced drag under the condition that4只 and C″were varied wh■eFヮ and θデ were kept constant.As a result of thisexperiinent,the strong vortex was found in the wake of the cylinder near the side―Wall(See Fig。 1). It iS thought that this vortex seems to be generated by the sec‐ondary flow of the boundary layer on the side‐wall and is concerned with the threc‐dilnensionality of the flow.In this report, we present he experilnental result obtained so far.*Department of Mechanical EngineeringFumio Yoshino and Ryoji Waka:The lnfluence of the Side=Wall on the Fユowaround the Circular Cylinder with Tangential lniectiOn OE AirFig.l The vortex in the wake visualized by means of the tufts method.(X/D=4.6,R,=0.5x10S,4尺=8 and cμ=0・22)2  NomenclaturesX = 工)istance from the center of the cylinder along the tunnel axis doヽVnstream;77 = Distance from the side一、Vall in panwise direction,Z= Perpendicular distance froHl the horizontal plane passing through the centralaxis of the cylinder;D = Diameter of the cylinder;bO= Width Of the slot;θ = Angle measured clockヽVise froFn the leading edge;θ′= Angular positiOn of the s10t lneasured froHl the top of the cylinder dOWnstr‐eam;θysP&θとsP = Angular positions of the upper―and the lo、Ver―separation points onthe cylinder, respectively;Ps= Static―pressure on the surface Of the cylinder;P∞= Static―pressure l■the wind tunnel;C, = Static―pressure coefficient   ( = 撓  ),C,ぅ= Base―pressure coeffiCient,）???〓???t i  RёPorts ot the Faculty of Engittёering,TOttOri University,Voユ.6Cた= Sectional lift COefficient,                  ― 十Crt= Momentum むoёfficiさnt Of jet(.下 司ラ豆デ::τl多瓦ラー ),″ = wlomentum of iet at the outlet of the slotiRヮ=Reynolds number(=y∞= Tunnel speed;4R = Aspect ratio of the cylinder;P忌じフ = Density and kinematic viscosity ёoefficients of air in the 、vind tunnel,respectively.3 Experi】mental installlllent and methodThe experimental apparattls was the same that we had used before'). The exp‐erilnent was carried out under the conditiorl that R, and θデ vere constant,that is,2,lx105 and O° ,respectively.The measurements of the static―pressure on the cylinder were made at three asp‐ect ratios, 4, 6 and 8, by properly varying Cμ from O to about O,3, However the obs‐ervations of the flow and the other measurement described below were made atonly one aspect ratio,8, and in some narrow range of Cr from O to about O.25,but,in this case,翼。 and ιl「 were remained unchanged.The streamline on the side―、vall wa  visualized by using the tufts method.ふ江ore‐over the streamlines on the cylinder and the side―wall ivere visualized by using theoil―flow method.  Finally we measured the static―pressure in the symmetric planeincluding the center of the span in it. It was measured by means of the disk―statichead、vith round edge, This disk has di=nensions of 15 η″η in diameter and O.3η%in thickness and is drilled the static―pressure―hole of O.5 知″修 n diameter at thecenter of it. In this measurement, 買, was l.5x10S,since the vibration of the diskwas too large to measure accurate static―pressure.4 Results and DiscussionThe results of this experilnent are represented in graphs and pictures.Fig。 2 shows the separation lines of the flow in the spanwise direction. In thisfigure, the symbols indicate the separation points obtained from the static―pressuredistribution on the cylinder and the lines indicate the separatibn lines obtained fromthe oil‐f ow method(see Fig. 6). The larger the Cris,the later the upper‐separationis,however the lower―separation is scarcely influenced by Cr・ When Cμ= 0, the???Fu“liO Yoshinc and Ryoil Waka:「rhe lnfluence of the Side―Wall on theFlow arolnd the Circular Cylinder with Tangential lnieCtiOn of Air?? ??〕????? ????? ?????? ???。????。?。?。?。?。?。?．。????。???。????。?ets, 500Fig。2 The separation lines on the cylinder.Yw/D40      30      20      10      0Fig,3 The spanwise distribution of Crs.upper―and lower―separation lines are allnost straight except very near the side―wall. On the other hand,when Cμ】>0, the upp r―se a ation line is varied in span―wise direction so much ;the separation point begins to move gradually toWard doW‐nstream from someWhere about r7/D - 1.5 and reaches the farthest point at about77/D = 0。7, after that it retreats rapidly as approaching to the side―wall.Fig。 3 shows the spanwise distribution of Crs. C′ is al nost cOn tant over the、7hOlespan when Cr=0,When Cμ> Os iS also almost constant as far as about r7/D≧1.5, hoWёver it decreases rapidly near the side―wa l. WIoreover the larger the Cμ is,the larger the rate of decrease of Cys near the side―wa1l is.Fig. 4 shows the spanwise distributiOnof Cb´. When CP= 0,C´b is all■ost cOn‐竃監耳顎qt税♭【hi二i∬::・mttV猛:扇 YジDbegins to decrease rapidly from someW‐   好6here about y7/D = 1・5 and reaches the   :&!旱fminimum value at about r7/D= Oo6,   転4then it increases rapidly as approaching :ユ9息子to the side―wall.Fig.4 The spanwise distribution oF C,b.It is found froni these figures that theflo、v around the cylinder may be consid‐ered approxilnately two―dilnensional in the region from the center of the span tosomewhere about 77 貴 1.5, if induced velocity is ignored, since the characteristicvalues like C,b, θ,sP and CJs of the flow in this region are alinost the same as thoseat the center of the span.  The influence of the side―wall Stro gly appear  in pa‐rticular near the side―wall, that is, in the region from someWhere about y7/D =1,5to the side―wall. However it is thought that the f10W patterns near the side―wallare qualitatively Jike and is independent of AR tthen CP>O or,in other words,isa function of the distance only from the side―wall, since all the variations of theReporta cF the Facultty Of Engineering,「rOtt。■二univereitt7,V01・6characteristic values near the side―wall occur within the same range from the wallirrespective to望4R.Re=2 09XlざAR= 8Cμ =OC,bF-1 26eut,= 1127°el.,= 282.3Re=2 09XldAR= 8Cメ i O.238C,b=―O08eu.,= 161.O°ell。・ 2665°Fig.5 The streamlines on the side‐wa11.000(SIot)180270ら=0090(SIot)Cど=0.252Fig.6 The streamlines on the cyユニnd r visuanzed by means Of theoil■low method.g鬱=2 1×05)Fig. 5, Fig. 6 and Fig. 7 shoW the streamlines on the side―wall, on he cylinderand the static―pressure distributions in the symmetric plane at the center of thespan,respectively. Fig. 5 is obtained from tufts method (solid lines) and Oil―flowmethod (dotted lines, see Fig. 8). Fig. 9 shoヽvs the equal―staticpressure lines aro・und the cylinder obtained from Fig. 7.When Cμ= 0,it is found froni these figures==、 ｀~―― ―＼ヽ｀ ｀ ―___(→ ― ― ― ― ― ― ―=二上4/″~~~Fumio Yoshiio and Ryoji Waka i The lnfluence of the Side―Wall on theFlow around the Circular Cylinder with Tangential lnjection of AirAR=8膏と:♀46 X iODCpb=―12630X/D-50…CPFig.7 The static‐pressure distributioAS arOund the cylinder in the syH metric Plane.Cμ=O                             Cμ=0249Fig.8 The streamlines On the side_wall visualized by means of the cilfiow method.cF9=2.lx105)that the flow is allnost sy■llnetric with respect to X axis and the influence of theside―wa■on the flow is not seen so clear.When Cμ>0,hOWeve ,t e static―pre sureof the fiow is iower at the upper―side than that at the lower―side of the cylinder(see Fig。 9). ThiS indicates that circulation around the cylinder arises, sO that aer‐odynaH?cal force actS on the cylinder. On the other hand, the strea■1lines n tlleside―wall direct upwards behind the cylinder. This may be thought as follows ;AR・8C"=q249Rei 146 kCpb―O.15??????????????rr/Cp=o＼Reports of the Faculty of Engineering,TOttori University,Vol.6皇を三!:愁箋105Cpb=-0.15Cp=-0 75       Cp=-05AR= 8侵ど:三  !.46)(105Cpb=-1.261// Cp=―o5Cp=-075＼ Cp=-10 CP=0、さ cp=-025CP=(上5 ヽ X/DCP=-075Cp=-05Fig.9 The equalttstatic‐pres ure lines around the cyユinder in the symmetric Plane.the static―pressure gradient around the cylinder is not s:'mmetric and the static―pressure on the upper―side is lo、ver than that on the lower―side.  Therefore thesecondary flow ought to be directed upwards behind the cylinder(See Fig. 8).lヽoreover a strong vortex appears on the cylinder near the side―wall(see Fig. 6)and it is shed from the surface of the cylinder.  The central position of thisvortex which rotates counterclockwise is about r7/D=0・6 regardles of ARand it nearly coincides with the position of the vortex observed in the 、vake(see Fig。 1). And this voftex seems to have a certain relation to the secondary flo、von the side―wall.Concludingly, it is thought that the variation of the characteristic values nearthe side―、vall are caused by this strong vortex,which means that those variationsare the function of the distance frottl the side一、vall and not of AR.5 Conclusion(1)The strong vortex exists on the surface of and in the wake of the cylinderヽVhenCμ〕> O and it is shed fro■l there downstream.(2)The f10W around the cylindeF iS COnsidered to be nearly t、vo―dilnensional in theregion frotti the center of the span to 77//D≒1.5, but it is necessary to take//よヾCp=025B      Funお,Yoshino岳nd Ryeit W餌ぬ:The rnflusnω ol,the Side―Wan_on theF二ow around the Circular Cylnder with Ta4gential 14卜CtiOn oE Airinduced velodty into account.(31 All the characteristic values aFe funCtions of the dおtance from the side工walヽnot of ttt,and he variations.of those are related to the vortex mentioned in位).Referenceつ Ful■ya and YoslinoP Buli`JSME,18■23c1975-9J,1002つ Furuya,Yoshino and Wak4,Preprint of Bulleth Of JSME and JSPE,cn Japanese), tShOWa49_1り,7.

The Influence of the Side-Wall on the Flow around the Circular Cylinder with Tangential Injection of Air

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The Influence of the Side-Wall on the Flow around the Circular Cylinder with Tangential Injection of Air

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