"At the request of the Junkers Aircraft and Engine Construction Company, Engine Division, Dessau Main Plant, an investigation was made using the interferometer method on the two turbine-blade profiles submitted. The interferometer method enables making visible the differences in density and consequently the boundary layers that develop when a flow is directed on the profile. Recognition of the points on the profile at which separation of flow occurs is thus possible" (p. 1)

von Vietinghoff-Scheel, K.

UNT Digital Library

.— —... ..&. : ~—— -+...,=*--- *.“.. - ,, ,-...?NATIONAL ADVISORY COMMITTEEFOR AERONAUTICSJUfi 4;:~~;!TECHNICAL MEMORANDUMNo. 1171LABORATORY REPORT ON THE tiSTIGATION OF THEFLOW AROUND TWO TURBINE -BLADE PROFILESUSING THE INTERFEROMETER METHODBy K. von Vietinghoff-ScheelTranslation‘ ‘Versuchsbericht fiber die Untersuchung der Stromung um zweiTqrbinenschaufelprofile mit Hilfe der Inter~erenzmethode~” DeutscheLuftfahrfforschung, Untersuchungen und Mitteilungen Nr. 2096Luftfahrff orschungsanstalt Hermann Goring E. V.Institut fur Motorenforschung, Braunschweig, Germany, ZWBMay 31, 1944WashingtonJuly 1947: Illllllllllllllmmlufllllllllllllllll31176014415625— —NATIONALADVISORYCOMMITTEE FOR AETK)NAUTICSTECHNICALIABC)RATORYREPORTwomm NO. 1171ON TE3 INVE3TIGATIONOF T13XFLOW AROUND TWO WINE -BLADE PRQF13iESUSING THE INTW3?EROMETERMETHOIYBy K. von Vietinghoff-ScheelI. PURPOSX AND AIM OF INVESTIGATIONAt the request of the Junkers Aircraft and ~EcgineConstruc-tion Compa,ny,Engine Division, Dessau Main Plant, an investigationwas made usin~ the interferometermethod on the two turbine-bladeprofiles submitted.The interferometermethod (reference 1) enables makins visiblethe differences in density and consequently the boundary layersthat develop when a flow is directed on the profile. Recognitionof the points on the profile at which separation of flow occursis thus possible. By means of the interference photographs theextent of the dead-water region may be a~certained. The size ofthe dead-water region provides evidence as to the quality of theflow and allows a qualitative eotimate Oi’ the amount of the flowlosses. Interference photographs “Lhusprovide means of judgingthe utility of profiles under specific operating conditions andprovide su~&estions for possible changes of profile contours thatmight help to improve flow relations. Conclusions may be drawnconcerning the influence of the blade-spacing ratio, the inlet-air angle, and the connection between the curvature of the profilecontour and the point of seyara~ion of the flow from the profilesurface.In addition, interferencephotographs also make possibleascertainment of the distribution of pressure and velocity overthe blade. Such quantitative evaluation of the interferencephotographs was not undertaken in regard to the present experiments.*“Versuchsbericht~ber die Untersuchung der Str8mung urnzweiTurbinenschaufelprofilemii Hil.feder Interferenzmtitho de,”DeutscheLuftfahrtforschung,Untersuchungen und Mitteilungen Nr. 2096,iwftfahrtforschungsanstaltHermann G&ing E. V., Inst. f. Motoren-forschung, Braunschwei&j Germany, ZWB, May 31, 1944.,.,2 NACA TM No. U.71The rotor blade midsyan sections for “I” and for “III” wereinvestigated. Hereinafter the first blade will be designatedprofile I and the second, profile 11.From the data submitted, it ayqears that the blade sectionsoyerate in the turbine under the following conditions: t, cascadespacing; 2, blade choqd measured as the normal projection on awtraight line tangent to the concave side of the blade; PI, inlet-air angle [NACA comment: As specifically defjned ir,next paragraph;P2, exit angle:ReProfile I 0.676 30-53° 34.6°’>-250,000profile II .676 30-33° 35.5° ‘III. SETUP AND CONDITI01U3OF EXPERIMENTSFigure 1 ehowa the Zehnder-Mach interferometerand the cascadetunnel jn which the blades were installed for the investigations.In figure 2 are shown cross sections of the tunnel, which can beused for investigations involving inlet-air angles from PI = 20°to pl = 90° and turning a~l.es Pu between 36° and 145°. “lnlet-air angle” is here defined as the angle between the cascade lineand the direction of the incident air flow, at the cascade line;the direction pointin~ from the pressure side to the suction sideof the profile is designated the positive djrection.The air is sucked by an exhauster through the inlet duct a,which is square in cross section and yrovided with an entrancefairing (i’ig~.2(a) and 2(b)). The air then flows through the two-dimensional cascade b. The air stream freely emerging from thecascade is collected by the collecting funnel c and led to theexhauster through the diffuser d and a duct elbow attached tothe diffuser by a flexible leather sleeve. The front and rearwalls f of the air channel ahead of the cascade can swing aboutthe two axes g. Thus the cascade can be investigated in operationat variou~ inlet-air angles. For each inlet-air angle a differentinlet duct a may be attached to the cascade tunnel. Also, foreach exit an@e a different diffuser can be bolted to the base @ateof the tunnel. During each experiment, the diffuser is shifted.onthe base plate until equal static pressure exists in both deadspaces m and n. The two windows i are built into the strongNACA ~-No. 1171side walls h of the cascade tunnel in parallel planes. (Seefig. 2(b).) The blades b are held firmly in the tunnel by twotension.wires k of 2-millirn6tcr diameter and are kept fmmcontact with the glass windows by rubber pads 2 glued to theends. (See fig. 2(b).)The model blades were manufactured hers from commerciallyprocessed beech wood. In making the blades, special emphasie waslaid on keeping the spanwise sections the same. The surface ofthe model blades wae lacquered.The spacing ratio t/2 = 0.676 could not actually ~e attainedwjth the model blades jn the air channel. Therefore, profiles Iand II were each investigatedat two syacinG ratios t/1, nameIy,profile I at t/2 = 0.658 and 0.824 and profile II at t/1 = 0.638and 0.800. In order to obtain a better survey of the behavjor oi’the two profiles, the range of inlet-air angleo was extended inboth directions.In most of the experiments hereinafter described, one bladeof the cascade was slightly heated. For this purpose the bladewas provided with a hole o (figs. 2(a) and 2(b)) into which wasinserted a heating coil wound on a ceramic tube. In the photo-&ral]hs,the shadow of the electric cord leadi~ to thi~ heater isvisible. The position of this cord.chanGes with the inlet-airangle. Its direction ngrees very exactly with that of the incidentflow ahead of the cascade. Theoretical considerations indicate thatthe flow field is not influencedby temperature differences if thecharacteristicsof the fluid(density and viacosity)are independentof temperature. Because the temperature differences arising inthis case between the blade surface and the air flowing Tast donot, on the basis of the invest-igations,amount to more than 20° C,the heati~ can have nQ marked effect on the boundary layer and itsyoints of separation.III. DISCUSSION OF INTERFTXENCEPHOTOGRAPHSFi@_me 3 shows an interferencephotograph with no air flow inthe test tunnel. The interferencebands run as straight linesparallel to one another. The black shadows seen in the two ri6ht-hand corners of most of the photographs are simply the frame ofthe observation window. When a flow occurs around the blades, afield of density variation arises. Thereby the bands are deflectedfrom their original positions in proportion to the local densitydifferences. In potential flow, a continuous curvature of the. . —4 NACA ’114No. 1171bands occurs as a result of adiabatic change of state; these bandsmay be noted particularly near the stagnation ~o,intbecause of themore pronounced pressure and density changes oca.nwing there. Abend occurs in the bands at the boundary layer because of the tem-perature rise produced by friction. Ascertainment of the develop-ment of the boundary layer alonG the profile surface and the pointof separation is thus possible. In certain cases it is im~ossibleto decide without further evidence whether what is observed is athickened boundary layer or a yartjal separation of the flow. Thedead-water region is usually characterizedby bands running approxi-mately parallel to the undisturbed bands but shifted relative to theundisturbed bands in a d~rection normal to the bands.Profile I: tjz = 0.658 and 0.824, figllres4 to 13. - Profile Ioperates in the turbine with a spaci~ ratio t 2 = 0.676. Thisspacing ratio lies betw-eenthe values t/1 = 0.658 and 0.624.The flow around this profile was investigatedat six differentinlet-air angles with the smaller spacins ratio and at four differen-binlet-air angles with the lar~er spacing ratio.Fi@re 4 shows the interferencephotograph made with t/1 = 0.658and the in~et-a~r nwle PI = 20°. In this case, the inlet-air angleis substantially s?nallerthan the exit angle. The flow is thereforeretarded by the cascade. The flow had to be markedly i-etardedu~onentering the channel between the blades if it was to fill this spacecom-pletely.Because the flow cannot overtone the press’urerise con-nected therewith, it separates :rou the back of the blade behind thestagnation point. ‘l’hedead-water region cccupies about three-fourthsof the flow channel. It is only on the concave side of the blade thata mall region o.?satisfactory 71OW can be found, althouah the flow inthe interblade channel is a~a;inaccelerated. The blade was unheatedwhen this photograph was taken. Tliepronounced separation may be seenin figure 4 on the back of the ,left-handand center blacdes. Theright-hand blade, however, behaves differently. It is not similarlysup~>liedwith an unobjectionable flow because the leadin~ edge ofthe yrofile is too near the rear wall f of the air channel aheadof the cascade (rig. 2(a)).Profile I was also investigatedwith both spaci% ratios at thefollowing inlet-air angles: !31. 25°, 34°, 40°, and 48J; and withthe smaller spacing ratio at ~~ . 9CP in addition. The resultingphotographs comprise figures 5 to 13.NACA TM No. 1171 5.J .-A% the inlet-air angle of 25°, a separation immediatelybehindthe leading edge again appears with both spacing ratios (figs. Sand 10)w This separation is -connectedwith the ‘factthat the angleP1 = 25° is still too small for satisfactory flow relations and,conversely, it is also caused by the sudden transition in thecurvature of the back contour. Apparently, in both cases the dead-water region narrows in the direction of the flow as far as thepoint where the arc turns into the straight line; thereafter thedead-water region again broadens. The dead-water region increaseswith the spacing; therefore, the flow losses increase.With the next inlet-air angle, 34°, (figs. 6 and 11) at whichthe blade operates with approximately zero pressure drop acrossthe lattice, a separation on the back behind the sta~nation pointstill occurs. In figure 11 it is just possible still to recognizethis separation in a discontinuity in the course of the bands nearthe surface of the profile. In both spaci~s, the dead watercould have been observed more distinctly if the interferencebandshad been arranged to run at right angles to their actual directionin fig.mes 6 and 11. The dead-water re~ion is smaller than whenPl = 25° but it attains a considerableextent at the straightfinal portion of the back s~mface. Probably the long trailinged~c of the blade could be somewhat shortened without changingthe flow around the blade.The next inlet-air angle, B1 = 40° (figs. 7 and 12), is thefirst one at which the separation from the back of the bladebehind the stagnation point is almost entirely eliminated. Thedead-water re~ion at the straight final portion of the back sur-i“aceis also smaller. When the inlet-air angle is increasedto 48° (figs. 8 and 13), the relations become still better; theinterferencephoto~raphs show a separation on the back of the bladeonly at the point of transition from the arc contour to the straight-line yortion of the back. This separation may be observed with bothspacings.If the inlet-air angle were to be increased still further, aseparation would occur on the front side downstream oi”the leadingedge. This phenomenon is especially unmistakable at 131= 90° infi~ure 9; on the front side downstream of’the impact point theflow does not follow the contour of the profile but separates atthe leading edge. In this experiment, the blade equipped with theheating coil was not heutad. On the basis of the interferencephotographs taken, profile I does not operate altogether satis-factorily in the range of inlet-air angles ~1 = 30° to 33°.6 NACA TM No.-ll?lThis statement applies to both snacing ratios; with the lar$erspacing ratio the losses are greater, ~fienwith 131= 34°) certainlosses must still be expected. Not until 131 amounts to about 40°or more does the flow become satisfactory over the greater part ofthe back contour.The separation occurrinfj close behind the stagnation point atsmaller inlet-air angles seems to Influence markedly the flow at thepoint of transition from tha curved contour to the straight portion.In any case, the sharpness of the yrofile nose is not recommended.ITofile II: t/2 = 0.638 and 0.800. - Profile II was also investi-——gated for two spacing ra~ios. The value specified, t/2 = 0.676, liesbetween these two syacings. The investigationof this profile includedthe four inlet-air angles PI = 25°, 34°, 40°, and 48°. The photographsobtained comprise figures 14 to 25.On the basis of previous experience, a marked separation on theback of the blade near the impact point was to be assumed a“~ (1~ = 20°.This separation is still present at 131= 25° althouah the dead-waterregion does become smaller. Th3s is seen in figures 14, 18, and 19.Particularly at the larger spacing ratio the dead-water regior.is oflarge extent. At the next inle-L-airangle 131= 34°, the extent ofthe dead-water region does decreasebut a separation c,nthe back nearthe stagnation point still occurs as may be ascertained from the bendin the interferencebands near the profile surface in figures 15, 20,23, and 24. Here again the interferencephotographs indicate thatthe losses increase with increased spacing.At the inlet-air =@e Pl= 40°, a marked improvement alreadyexists as compared with B1 = 34°. At only the larger spacing ratiodoes a small degree of separation seem to occur behind the leadjngedge (figs. 21 and 25); at t~l = 0.638, this separation of theflow is not unequivocally recognizable (fig. 16). Of course, inboth cases a separat~on occurs at the ~oint of transition from thearc contour to the straight final portion of the back surface; thisseparation is caused by the sudden change in the curvature.At 131= 48° (fiSs. 17 and 22), the separation on the back nearthe stagnation point disappears jn both syacjng ratios and only theseparation of flow at the straiGht final portion of the back surfaceremains. With further increase of the inlet-air angle, a separat~onon the front side of the profile would gradually develop; thisdevelopment would a&ain lead to greater flow losses.NACA TM NO. 1171 7From the comparison of the two profiles, it may be concludedthat the flow around profile II is scarcely more favorable in spiteof the rounding of the leading edge. Probably the radius of thero’mding is too small to prevent a separation at inlet-air an@esother than the most favorable one. The results obtained indicatea most favorable inlet-air angle that is in every case larger thanthe angle of shock-free entry derived in the usual manner from theproi’iledrawing.Translation by Edward S. Shaf’er,National Advisory Committeefor Aeronautics.1. Ecksrt, E., and von Vietin&hoff-Scheel,K.: Versuche ~ber dieStr&nznG durch Turbinenschaui’elgitter.Vorabdrtickefrom:Jahrb. 1942 d. 1).Lufti’ahrtforschung,Lfg. 5-6. Tech.Berichte, Bd. 9, Nr. 7, 1942.u^Section A—p6.^—Aa► .NACA TM No. 1 171	F i gs. 1, 2l 1Fi gu re Ililra	 Inlet ductb	 CascadeC	 Collecting funneld	 Diffusere	 N i p p I es for p ressu re-equ a l i zat i on I i n esf	 Front and rear wallsof inlet channelg	 Axes upon whi ch wal I sf turnFi gu re 2h	 Si de wal I si	 p a r a I I el—pI ane gl ass wi ndowsk	 Ten s  on wi resI	 Rubber padsm, n	 Dead spaceso	 Ho I esp	 Adjusting screwsr	 Tap s fo r p ressu re measu rements	 Holes for pitot tubeNACA TM No. I 171 Figs. 3, 4, 5Figure 3Figure 4Figure 5t~z = 0.658P, = 25°Re = 294,0001 —.NACA TM No. 1171Figure 6Figure 7Figure 8Figs. 6,7,8tIZ = 0.658P, = 34°Re = 283, W0t/Z = o.658p, = 40°Re = 260,000tlZ= ().658P, = 48°Re = 230,000NACA TM No. I 17 IFigure 9FigureFigure10IIFigs. 9,10, tlt~l = 0.658P, - ~“Re = 155,000tll = 0.824 [NACAcomment: Val uecorrected from theGerman. ]~1 = 25°Re = 279,000tll = 0.824P, = 34°R~k 257,000NACA TM No. I 171Figure 12Figure ISFigure 14Figs. 12, 13, 14t// = 0.824P, = 40°Re = 241,000tfZ = 0.024P, - 40°Re = 216,030tl) = 0.638@l = 25°Re = 285.000hJACA TM No. ii71 Figs. IEJ, 16, 17Figure 15FigureFigure1617W2 - 0.63%PI - 34°Re= 271, 51XI~lZ = 0.638P, “ ~“RO = 253,000tlz = ().638P, “ e“R. = 215,000~—...-l.—. -—(J1’(W/,,NACA TM No. .1171FigureFigureFiguro181920Figs, 18, 19, 20t}t = Q.8Q0P, “ 25°Re - 266.000t/z - 0.800P, = 25°Re = 266,000tlz = 0.800P, = 34°Re = 25%000/’1’‘1,LJNACA TM NO. tFigure21Figure 22Figure 23171 Figs. 21.22,23tit = (3,80Q~1 . *ORe = 246,000tlz = Q .800$, = 48°Re = 223, oootlz = 0.638P, = 34°Re= 271,500———NACA TM No. I 17 I. .Figure 24Figure25Figs. 24, 25w = O.aooP, = 34°Re = 255,000tlt = 0.800$1 = W“Re = 246, Wo;- .’--’-’Illlllllllmmmtllnll~‘4‘1. ,+1‘i ‘“)V’J.. ,.F.’:’. .,,’ .0,.,;, ,,,.. ,,, ,,, ,.,. -—--,- —, ,-—,-, , , , m1 nl= -—lIM1 ■ ■ Imllllmllll Im 1 lml 1111, ,, I11111, ,,

Versuchsbericht über die Untersuchung der Strömung um zwei Turbineschaufelprofile mit Hilfe der Interferenzmethode

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Versuchsbericht über die Untersuchung der Strömung um zwei Turbineschaufelprofile mit Hilfe der Interferenzmethode

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