vortex wake alleviation prediction

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NASATechnicaPaper24421985

NASAN t iorial Aeronaut icsand S p a c e AdministrattonScientific and TechnicalInformation Branch

Vortex Wake AlleviationStudies With a VariableTwist WingG. Thomas Holbrook,Dana Morris Dunham,and George C. GreeneLangley Research CenterHamp ton, Virginia


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ContentsSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Test Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Langley 4-by 7-Meter Tunnel . . . . . . . . . . . . . . . . . . . . . . . 4Hydronautics Ship Model Basin Water Tank . . . . . . . . . . . . . . . . . 5

Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Variable Twist Wing . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Trailing Wing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

TestMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Presentation of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Effects of Facilities and Measurement Techniques . . . . . . . . . . . . . . . 7Predicted and Measured Vortex Wake Development . . . . . . . . . . . . . . 8Effects of Continuous Span Load Distributions . . . . . . . . . . . . . . . . 10Effects of Partial-Span-Flap Span Load Distributions . . . . . . . . . . . . . 11Effects of Alleviated Vortex Wake Configurations . . . . . . . . . . . . . . . 12

Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Appendix A -Test Method Details . . . . . . . . . . . . . . . . . . . . . . 78Appendix B-Experimental Influences . . . . . . . . . . . . . . . . . . . . 84References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

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SummaryVortex wake alleviation studies were conducted

in a wind tunnel and a water towing tank using thevariable twist wing, a vortex-generator model capa-ble of controlled and measured variations in spanload. Fourteen different configurations of the mul-tisegmented wing model were tested at a Reynoldsnumber of 1 x lo6 and a lift coefficient of 0.6 in theLangley 4- by 7-Meter Tunnel and the Hydronau-tics Ship Model Basin water tank at Hydronautics,Inc., Laurel, Md. In the wind tunnel, detailed spanload measurements were taken and detailed near-wake data obtained with hot-film anemometer andtrailing-wing surveys. In the water tank , near- andfar-wake trailing-wing rolling-moment surveys weremade. The tests examined the roles of span load,drag, and turbulence distributions in vortex wakealleviation. An additional objective was to deter-mine whether relatively simple analytical predictionsof span load and wake roll up could realistically char-acterize the vortex generator span load and the re-sulting vortex wake development.

The variety of measurements allowed results to becorrelated and their accuracy to be checked betweentest facilities as well as between wing and wake mea-surements. In this manner, several facility and mea-surement technique effects were found to have signif-icantly influenced portions of either the vortex wakeroll up or the experimental quantification of vortexwake intensity. Detailed wind tunnel measurementsof span load distributions on the wing and cross planewakc velocities at a semispan downstream correlatedwell with each other and with water tank measure-ments of peak trailing-wing rolling moments. Thesedetailed measurements were used to show that invis-cid analytical prediction techniques accurately por-trayed the vortex generator span load distributionand initial vortex wake development to the resolutionlimits of the data. However, meander and flow angu-larity in the wind tunnel prevented, in other than aqualitative sense, the use of wake velocity data mea-sured at 6 an d 11 semispans downstream. Averagetrailing-wing rolling moments were shown to be un-reliable as a measure of the vortex intensity becausevortex meander amplification did not scale betweenthe test facilities and free-air conditions. High val-ues of meander amplification caused average trailing-wing rolling-moment da ta in both facilities, as well aswake velocity data in the wind tunnel, to falsely in-dicate rapid vortex decay with downstream distance.

A tapered-span-load configuration, which exhib-ited little or no drag penalty, was shown to offersignificant downstream wake alleviation to a smalltrail ing wing. This wing configuration achieved wake

alleviation through span load specification of moreuniform vorticity shedding at the wing trailing edge.In contrast , the greater downstream wake alleviationachieved with the addition of spoilers to a flapped-wing configuration was shown to result directly fromthe high incremental drag and turbulence associatedwith the spoilers and not from the span load alter-ation they caused.Introduction

Large aircraft produce vortex wakes which cancause severe roll upset to encountering aircraft withinseveral miles of the generating aircraft. To precludehazardous operations within airport terminal areas,pilots are advised (and required under IFR (instru-ment flight rules) conditions) to maintain longitudi-nal aircraft spacings of up to 6 n.mi. Should theserequirements be maintained into the 1 9 9 0 ~ ~he ben-efits of new four-dimensional terminal control andlanding systems technology may be limited. Thegrowth of air transportation capacity could thus beinhibited and its cost increased. Both near- and far-term solutions to the vortex wake problem are beingsought in a joint research program conducted by theNational Aeronautics and Space Administration andthe Federal Aviation Administration. NASA is in-vestigating vortex wake alleviation and the FAA ispursuing wake detection and avoidance technology.Portions of this research are compiled in references 1and 2 , respectively.

Since 1970, fundamental and applied vortex wakeresearch has been aimed at understanding the physicsof vortex fiows and determining t hc effects of thevortex-generating aircraft and surrounding atmo-spheric conditions on the vortex wake roll up anddecay. This work has encompassed a broad spec-trum of experimental, computational, and theoreti-cal aerodynamics (refs. 1 to 6); this broad-based ap-proach is necessitated by the extensive domain of vor-tex flows. From birth t o death of a typical aircraftvortex wake system, a vast downstream distance istraversed and flow regimes range from inviscid to vis-cous and laminar t o turbulent. This complex systemis immersed in an atmosphere that can influence thelife of the vortex system according to its turbulenceand stability levels. During this life cycle, the vor-tex wake is generally believed to pass through threeless-than-distinct phases: (1) vortex generation androll up, (2 ) a stable, plateau region often exhibitingthe onset of mutual induction instabilities, and (3 )vortex decay and breakdown. Because each phase isuniquely suited to certain types of experimental andanalytical techniques, and since the wake exists oversuch a large downstream distance, most vortex wake


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research has necessarily been limited to independentinvestigation of each phase.

Another difficulty encountered in vortex wake re-search is the need for very detailed knowledge of thewing load distribution because the aerodynamic sta teof the aircraft or model serves as the initial conditionfor the transformation from wing flow to wake flow.To determine the relationship between wing load dis-tribution and wake development, however, a varietyof load distributions must be tested. Typically, thiswould require the use of several models, each exten-sively instrumented to obtain pressure distributiondat a. The cost of designing and building numerousmodels of this complexity is prohibitive.

For this invwtigation, the requirements for multi-ple span loads and large downstream distances weremet t)y testing a unique, pressure-instrumented vari-able twist wing (VTW) model both in a wind tun-nel. to obtain detailed wing and near-wake measure-ments, and in a water towing tank, where wake mea-surements were made at near- and far-downstreamdistances. The VTW, shown in figure 1, is amultiscgniented wing model capable of controlledand incasiircd variations in span load. This capa-bility elirni~iates he need for several models. Dragand tiirbulcnce distributions were varied using spoil-ers, splines, or drag plates.

Spoilers a n d splines have becn shown to be vor-t cx at t (lllliiit ors (refs. 7 to 9 ) because whcn prop-crly locat c d o i l a vortex-gcneriitor rnodc~lor aircraft,t li e wak(. o f the vortcx gcnerator imposes a reducedrolling nioiiicwt o i l a smaller trailing wing or aircraft.One spccific ot)jective of these tests was to determinehow spoilers alleviate the roll upset experienced byfollowing aircraft. Thus, spoilers were used as vor-tex attcnuator s in this investigation. However, thesplines arid drag plates were not applied strictly as at -tcniiators, but instead were used to control the dragarid turbulence distributions of the VTW.

Reduction of the rolling moment imposed on atrailing wing results from reducing the vortex tan-gential velocity over the region occupied by the fol-lowing modrl or aircraft. Peak tangential velocitiesare reduced by increasing the size of t he vortex core.An indicator of the vortex core radius is the vortic-ity dispersion radius, which characterizes the spreadof vorticity, either as shed at the vortex generatorwing or in the rollrd-up vortex wake. The vorticityccmtroid b / 2 and the vorticity dispersion radius (1aredinvtly aiialogous to the mean arid standard devi-at ion of the vorticity distribution shed at the wing( d I ( y ) / d y ) . (Sw ig. 2 . ) Similarly, in the wake, thevorticity ciistri1)ut on f2(y,2) deterrniries the vortic-i ty criitroicl (tlic l i i t c d ccntroid position is shownir i fig. 2 ) iilid the vorticity dispersiori radius, but the2

latter is now a function of time or downstream dis-tance. For a given input angular momentum, repre-sented by the vortex generator centerline circulationr o , the aim is to reduce the vortex wake roll upsetpotential to a small trailing wing by increasing thevorticity dispersion radius in the wake.

There are a number of ways to increase the vortic-ity dispersion radius. One direct approach is to alterthe span load of the vortex generator so that thevorticity dispersion is greater initially. In 1933, Betz(ref. 10) developed an approximate analysis describ-ing the relationship between the span load and thevorticity dispersion radius. Span load alteration hasbeen applied in several theoretical and experimentalworks. (See refs. 11 to 13 . ) A second method ofincreasing the vorticity dispersion deals with the dif-fusion of vorticity away from the vortex center, a pro-cess which occurs naturally because of laminar andturbulent viscous effects. In quiescent atmosphericconditions, if little turbulence is produced by the vor-tex generator, this process is much too slow. There-fore, the introduction of turbulence-producing de-vices on the vortex generator can enhance the growthof the vorticity dispersion radius in the downstreamwake. Another approach is to reduce the flux of an-gular momentum into the wake by increasing thevortex generator drag distribution locally. The in-creased drag creates an unfavorable axial pressuregradient and, if properly located, retards the localacceleration of the vortex sheet. Th e convective con-centration of the entire sheet is thus altered, and arolled-up wake with a greater vorticity dispersion ra-dius results. This effect is analogous to the vortexdeintensification that occurs as a result of includingthe wing drag distribution in a Betz inviscid wakeroll-up calculation, as described in reference 14 .

Splines increase the wing drag distribution locallyand thereby impose an adverse axial pressure gradi-ent on the vortex wake. Splines also increase theturbulence shed into the wake. (The original designmotivation for the splines, however, was the desircto create an axial pressure gradient. See ref. 8.)Spoilers produce all three effects, since in additionto increasing the drag and turbulence distributions,they also alter t he span load. This investigation usedthe span load tailoring capability of the VTW andalso made selective use of splines and drag plates forcontrolling drag and turbulence distributions in or-der to determine t he chief mechanism responsible forspoiler-produced vortex wake alleviation.

Fourteen different configuratiolis of the VTWwere tested to examine the roles of span load, drag,and turbulence distributions in vortcx wake allevia-tion with attention t o performance perialties 011 thevortex generator. An additional ohective was to


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determine whether relatively simple analytical pre-dictions of span load and wake roll up could realisti-cally characterize the vortex generator span load andthe resulting vortex wake development. Both the vor-tex generator and vortex wake measurements weresufficiently detailed to allow comparisons with theanalytical predictions of each and to enable an eval-uation of the test facility and measurement techniqueeffects. Appendixes A and B present test method de-tails and experimental influences, respectively.

wing aspect ratio, b2/Swing span, mvorticity centroid of wing liftdistribution relative to wingcenterline (does not includeeffects of lifting centerbody)(see fig. 2), mnormalized vorticity centroid ofwing lift distribution relative towing centerline (does not includeeffects of lifting centerbody)axial-force coefficient AxtApedrag coefficient (referenced togeometric angle of attack a ) ,i23drag coefficient corrected for pos-sible angle-of-attack inaccuracies,CN sin(a + ao )+ C A cos(a + u o )

900slift coefficient (referenced togeometric angle of attack a ) ,alift coefficient corrected for possi-ble angle-of-attack inaccuracies,CN cos(a + ao ) - C A sin(a + ao )

900s

Lift

centerbody lift coefficient,Centerbody lift900s

lift coefficient integrated fromright wing cp data,magnitude of maximum averageC1,Tw value measured for avortex of significant strength ina Y-2 ross plane with trailingwing at fixed y, z position

magnitude of maximum C~,TWvalue measured for a vortex ofsignificant strength in a Y - 2cross planetrailing-wing rolling-momentcoefficient, Rolling momentnormal-force coefficient,

900Ab

Normal force900s

wing chord, msection lift coefficient, Sec$zciftce at wing centerlinesection normal-force coefficientintegrated from chordwise cpdatastatic pressure coefficient,vorticity dispersion radius ofwing lift distribution relativeto vorticity centroid position(does not include effects of liftingcenterbody) (see fig. 2 ) , mindicesincremental length vector, mgrid square element length oninterpolated wake velocity grid,mindex for labeling vorticitycontour levels, where !&/Urn =f e n / 2 , n = 0, 1, 2, ...static pressure, Padynamic pressure, Paradius from center of vortex, mwing reference area, m2V T W semispan, mlift centroid position of wing liftdistribution (does not includeeffects of lifting centerbody) (see

time, sectotal velocity vector, m/sec

900

fig. 2), m

velocity components in X ,Y ,2Cartesian coordinate system,respectively, m/sec

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averaged velocity componentsin X ,Y ,2 Cartesian coordinatesystem, respectively, m/secinterpolated velocity componentsin X , Y ,2 Cartesian coordinatesystem, respectively, m/secright-hand Cartesian coordinatesystem originating at centerlineof VTW trailing edge with Xaligned to wind tunnel or watertank longitudinal centerline, Yaligned horizontally along rightwing and perpendicular t o X .and 2 aligned vertically upward(see fig. 3)VTW body axis aligned withlocal chord and originating atwing leading edgelongitudinal, lateral, and verticaldimensions along X ,Y ,2 Carte-sian coordinate system, nidimension along XLEaxis, mlateral vorticity centroid of VTWwake relat ive to wing ccmtcrlinc,111

y riiagnitutle at which C~,AVnicasurement oht ained, my value of vortex center deter-mined from wake velocity mea-surcnients, mgeometric angle of attack of wingcenterline chord, degangular offset between free-stream velocity and a = Oo , (legwing segment twist angle relativeto wing centerline chord (wingsegment leading edge up isposit ivc), drgvorticity dispersion radius for aGaussim distrit)ution of vorticity,I r icircrilat oi i Iricwurcd over wakesurvcy cross plaii~ll seitiispaiiwakr of VTW (see fig. 2 ) , 111~/sec

I 'o

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P

R

circulation a t wing centerlineas derived from lift distributionmeasurements (does not includeeffects of lifting centerbody) (seefig. 21, m2/seccirculation distribution alongVTW semispan as derived fromlift distribution measurements(does not include effects of liftingcenterbody) (see fig. a ) , m2/secdensity, kg/m3standard deviation of u elocitycomponent, m/secstandard deviation of w velocitycomponent, m/secstreamwise component of vortic-ity measured over wake surveycross plane in semispan wake ofVTW (see fig. 2 ) , sec-l

Subscript:00 free-stream conditionsTest Facilities

Two test facilities were used in this investigation:the Langley 4- by 7-Meter Tunnel and the Hydro-nautics Ship Model Basin (HSMB), a water towingtank at Hydronautics, Inc., Laurel, Md. The windtiinnel tests emphasized detailed model aerodynamicdata and detailed near-wake data, whereas the wa-ter tank tests were used primarily to collect far-wakerolling-momcmt data.

Langley 4- by 7-Meter TunnelThe test section of the Langley 4- by 7-Meter

Tunnel (fig. 1) has a height of 4 .4 2 m, a width of6.63 m, and a length of 1 5 .2 4 m. The VTW w asbladc rnounted atop a sting in the upstream end ofthe test section, near the entrance cone, and rnain-tainetl at test section centerline during test runs. An-gle of attack w as determined from an accelerometermounted in the fuselage. A six-component strain-gauge balance w a s used t o determine lift and dragfor the wing and centerbody conibinat ion.A survey rig, also pictured in figure 1, w as usedin t hese tests for Y,2 cross plane sampling of eithert hc. t hrce wake vc.locity colnponrlit s or the rollingIlloiiic~nt11 a trailing-wing rnod~ln the VTW wake.Tlici siirvey rig could be positioned ir i th e test sectionfrom 1 to 11 se.mispans behiiid the VTW. Either ahot-film probe or a trailing-wing 1110ddw as mounted


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to the motor-driven traverse mechanism on the sur-vey rig t o allow both la teral and vertical movements.Digital encoders on the traverse mechanism providedthe lateral and vertical position of the sensor duringtest runs.

Hydronautics Ship Model Basin W ater TankThe HSMB is a water towing tank facility 125 m

long and 7.32 m wide, with a water depth of 3.81 m.Two independently powered carriage systems wereused to propel the VTW and trailing-wing modelsthrough the tank. (See fig. 3 . ) The VTW quarter-chord line was located 1.12s below the waterlineand the model was attached overhead to the leadcarriage by a blade mounted to a tilt table. Thetilt table provided for angle-of-attack adjustment.Variable reluctance force measuring block gauges(ref. 15), attached internally to the VTW centerbody,measured lift and drag from the model wing only.(Centerbody forces were not measured.)The trailing-wing carriage had a motor-drivenscan system which traversed 46 cm vertically duringeach run at a rate of 4 cm/sec through the wake ofthe VTW. The lateral position of the blade-mountedtrailing wing was changed manually between runs.Separation distance between the two models wasdetermined using the time differential for the twocarriages to pass the midlength point of the watertank and the measured speed of the two carriages.Prior vortex wake work in this facility indicatedthat 15 rriinutes between runs was sufficient timeto allow the model-induced turbulence levels in thetank to damp t:, quiescent conditions. hlthoiigh theturbulence was not measured directly, a comparisonof flow field steadiness at z/s = 11 in both testfacilities indicated a substantially lower turbulencelevel in the water tank.Models

Variable Twist WingTwo variable twist wing (VTW) models were

used during th is investigation: an extensively instru-mented aluminum model which provided force andmoment data as well as detailed span load measure-ments in the wind tunnel, and an anodized aluminummodel which provided force and moment d at a only inthe water tank. The wind tunnel VTW was mountedatop a faired support strut which attached to thecenterbody. The water tank VTW was mounted be-low a faired supp ort st rut which attached to the tailcone. Other than model installation differences, theVTW models were geometrically identical and werethe same size.

The VTW model is shown mounted in the windtunnel in figure 1, and a schematic with dimensionsis shown in figure 4. The model had a metal wingwith an aspect ratio of 7, a span of 2.489 m, and anNACA 0012 airfoil section. The wing consisted of72 segments (each 2.96 cm wide and independentlyrotatable about its quarter chord), with 36 installedon each side of a wing center panel of 35.56 cmspan fixed to the centerbody. A body-of-revolutionwing-tip cap was fitted to each wing tip and twistedin unison with the final outboard wing segment.Spoilers, splines, or drag plates were added to severalVTW configurations, as shown in figure 5. Thesedevices were centered at y/s = f0.607 and thesplines and drag plates were mounted aft of thetrailing edge at about z / s = 0.122 (or z/c = 0.43).

The wind tunnel VTW model had 580 pressuretaps for measurement of spanwise and chordwisepressure distributions. Pressure coefficient da ta wereobtained along 19 spanwise positions on the rightwing and 1 symmetrically matching position just leftof the wing centerline. Spanwise and correspond-ing chordwise positions of each pressure orifice aregiven in table I. Right-wing segments were hollowedto accept either pressure orifice tubing or electronicscanning pressure transducers and associated wiring.Generally, alternate segments contained the pressuretransducers, which accepted the pressure orifice in-puts from the adjacent segment through openings ineach side of the segment. These openings were sizedand located to accommodate up to 15' twist betweenadjacent segments without unscaling the openings tothe free stream. Pressure data were taken undercemputer contro! with a!! 580 orifices electronicallyscanned and recorded in 0.1 sec.

Thus, the VTW design allowed the span loaddistribution to be tailored via wing segment twist,and the pressure instrumentation permitted accuratemeasurement of the pressure distribution over thewing. Fourteen VTW configurations that differed ineither wing twist distribution or wing device installa-tions were tested for this investigation. The configu-rations, shown in figure 6, are categorized into threegroups-continuous span load distributions, partial-span-flap span load distributions, and alleviated vor-tex wake configurations. This grouping system dif-ferentiates between the configurations of group I ,which produced one predominant vortex per semi-span, and those of group 11,which shed multiple semi-span vortices. The configurations of group I11 weretested to examine the mechanism of spoiler-producedvortex wake alleviation. The configurations aregiven designations and are described in table 11.These groupings and configuration designations willbe utilized throughout the remainder of this report.

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Details of the wing twist distributions and wingdevice installations are given in table I11 and areplotted with the span load dat a.

Trailing WingMeasuring the rolling moment on a smaller wing

positioned in the wake of the vortex generator hasbecome an accepted means of quantifying the hazardposed by the vortex wake system of a particularconfiguration. (See refs. 16 t o 27.) The aspect-ratio-5.35 trailing wing used for these tests has a spanequal to 13 percent of the VTW span. A photographaiid dimensions of t he unswcpt trailing-wing modelinstalled o n t he wind t iinriel traverse mechanism areprcstwtcd in figiirc. 7. In each test facility, the modelwas rnoiinted 011 a roll balance and attached to atrav(mc mechanism capatdc of positioning the modelboth laterally and vertically as required in the VTWwakr. Thc trailing-wing balance used in the watertank tests also measured lift and drag. Positiveand negative lift on the trailing wing was used t odetermine i f it was in an upwash or downwash region.This dctcrmination aided in positioning the wingrtlat ivc t o major-strength vortices.Test Method

The VTW was testctl at a Reynolds nuriiber ofI x t)ased on wing chord, i i i tmth facilities.This coiidit ioti rrquirrd frer-st rcaiii dynamic prcs-siirc and volocity values of 1005 Pi t and 40.52 m/sec,rcq)cc.tivcly, i r i t h e wirid tunnel and 5049 Pa and3.179 n i / s ( ~ ,espcctivc~ly,n the watcr tank. All niea-siiroirieiits of VTW span load distributions, trailing-wing rolling i i ioInents , and wake velocities were madewith tho VTW at a CL f 0.6 to avoid stall overany twistcd portion of thc wing. Additional VTWaerodynamic data were taken through an angle-of-attack range in the wind tunnel. The types of da tataken i n this investigation are summarized in table IVaccording to downstream distance and test facility.(:encrally. t h e wind tunnel test was used to obtaindctailcd niodcl and near-wake data and thc watertank test was used to obtain far-wake rolling-momentda ta . The following paragraphs summarize each se tof nieasiircinents i n both facilities; details of the mea-surement tochriiqiies are presented in appendix A.

Wind tiinnel measiireiiients of CL and CD foreach VTW corifigurat on were taken from an an-glc of at tack of -4 to twyorid stall in iricrcnicntsof 2. ICxwpt o r i t l i c untwist cd wing configuration(VTW ) , wittcr i u i k iiic;tsiirciiicrits of t h e loiigitudi-i i a l ;wrociyii:tiiiic (1at it worv mad(. only at CL = 0.6.Scvrral factors i i i f l i i c w c d t l ie w*curacyand repeata-bility of t h ~ L itIi(l Cu iii(~tsiir(iiii(~iits1)taint.d in

both facilities. At CL = 0.6, force balance accu-racy for lift was within f4.5 percent in the windtunnel and f l . 1 percent in the water ta nk, whereasdrag accuracy of the utilized force balances was quitepoor-for a worst case situation, drag accuracy waspossibly only within f 5 3 percent in the wind tunneland f 25 percent in the water tank. The da ta signalsfrom both test facilities were low-pass filtered and av-eraged over long time periods to remove the effectsof model vibrations, flow turbulence, and qoo fluctu-ations. Although these techniques could not improvethe measiirenierit accuracy, they brought the overallrepeatability for CL o within f 3 percent in both fa-cilities and improved the CD repeatability t o withinf 7 percent in the wind tunnel and f 3 percent inthe water tank. This level of CD consistency wasadequate for the purposes of the present tests sincedrag was mcwured mainly to obtain significant CDdifferences between VTW configurations in the samefacility.

As noted previously, electronic scanning pressuretransducers were incorporated within VTW wingsegments for the wind tunnel test to allow computer-controlled recording of all 580 pressure orifice val-lies in about 0.1 sec. These values were then trans-forrried to c p data, integrated chordwise to obtainspan load pressure distributions, and integrated overthe right wing t o obtain the wing-alone lift coefficientC L , ~ .he accuracy of the electronic scanning pres-sure transducers assured that each chordwise cn inte-gration was within f0 .02 of the true value and tha toverall CL,?, rror w as typically less th an f 2 percent.Several parameters were computed from the mea-sured span load distributions for comparison with themeasured vorticity distributions in the wake and alsowith the trailing-wing rolling-moment data. The liftcentroid 3 , wing centerline circulation ro,vorticitycentroid b/2, and vorticity dispersion radius d werccalculated as shown in appendix A. This report em-phasizes span load data derived from the pressuredistribution measurements rather t han chordwise c pda ta . Complete chordwise arid spanwisc c p measure-ments for the VTW configurations tested in the windtunnel are given in reference 28.

Trailing-wing rolling-moment surveys of the VTWwake were made at four downstream distancesnear-field data were taken in the wind tunnel atx/s = 6 and 11, and far-field data with a near-fieldoverlap were taken in th e water tank at L / S = 11, 40,and 70. In the wind tunnel, thr trailing-wing rolling-moinent signal was sent through a 0.1-Hz low-passfilter and the output was averaged over a long pe-riod at each y , z survey point. I n t h c water tank,the trailing-wing rolling-momc.rit sigriiil was recordedwith a 20-Hz resolution in an a~ialog orriiat from

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which peak and long-period average data were deter-mined. In bo th facilities, a sufficient number of runswere made at each downstream survey cross planeto insure that the maximum rolling-moment coeffi-cient had been measured for each vortex of signifi-cant strength. These maximum rolling moments arepresented as C~,PKor water tank peak data and asC l , ~ vor wind tunnel and water tank averaged data .Wake velocity surveys were made in the windtunnel at three downstream positions (z/s= 1, 6,and 11) behind the right wing for each of four wingtwist configurations (VTW4, VTW7, VTW7S0, andVTW7S3). At each downstream location, semispancross plane surveys of u, u, nd w velocities wereniade using a three-component hot-film probe at-tached to the traverse mechanism on the survey rig.The hot-film probe traversed the cross plane contin-uously a t 1.3 cm/sec along about 55 horizontal rowswhich were separated vertically by 1.3 cm (0.01s)in high-vorticity regions and spread to about 5 cm(0.04s) apart near the upper and lower cross planeboundaries. Th e analog hot-film voltage signals weresampled at the r ate of 50 points per second and 0.02sspatial averages of probe position and flow velocitieswere computed in running-average fashion for eachhorizontal traverse. To compute vorticity (a)on-tours within each cross plane, the averaged velocitieswere linearly interpolated to a 0.02s (2.6-cm) meshgrid and vorticity was determined at the center ofeach grid square by taking the line integral of velocityaround thc square per unit area. Additional detailsof the computation of the vorticity cross planes canb o found ir , appendix -4. he interpolated vclocitieswere also used to determine the total circulation rand the lateral vorticity centroid position y in thewake cross plane for comparison with their counter-parts measured on the VTW, roand b/2.Presentation of Results

Results are presented under the five text subhead-ings listed in th e first column of th e table below.Figures pertinent to each subheading are also listed.Within each subheading (except that entitled Pre-dicted and Measured Vortex Wake Development) theresults will be addressed in th e following order:

Aerodynamic dataSpan load da taTrailing-wing rolling-moment da taWake velocity data

Additional overall results are presented in tables Vto VII.

Text subheadingEffects of Facilhies and

Measurement TechniquesPredicted and Measured Vortex

Wake DevelopmentEffects of Continuous Span

Load DistributionsEffects of Partial-Span-Flap

Span Load DistributionsEffects of Alleviated Vortex

Wake Configurations

TextPage

24

27

31

35

37

Pertinent,figures

B l - B l l

8--11

12-16

17-21

22-28

DiscussionEffects of Facilities and Measurem entTechniquesSeveral facility and measurement technique ef-fects were found to have significantly influenced por-

tions of ei ther the vortex wake roll up or the experi-mental quantification of vortex wake intensity. Thesefindings and their impact on the interpretation of thetest results are summarized here. A detailed discus-sion of these results can be found in appendix B,entitled Experimental Influences.

Aerodynamicdata. A comparison of the wind tun-nel and water tank V TW l aerodynamic dara from ailcy of -6" to 16' was made to ascertain that the CLand CD data correlated between facilities and thusthat the wakes shed at the wing trailing edge weresimilar. It was determined that CL and CD datacould be correlated between the test facilities onceangle-of-attack corrections were applied. Althoughflow angles were not measured directly in either testfacility, this and other investigations with the VTWand similar models indicated a wind tunnel cy cor-rection of about +0.5' due to flow angularity and awater tank cy correction of about -0.5' due t o refer-ence frame offsets. Application of these correctionscorrelated the two data sets well. Since CD is verysensitive to cy corrections (a 1' correction in angle ofattack changes C D by 33 percent) and because theexact cy correction for each facility is unknown, theCD data cited in this report are uncorrected and areuseful mainly for drag comparisons between VTWconfigurations in the same facility.

The survey rig was located at x/s = 6 or 11when aerodynamic da ta were measured through an (Y

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range. At these locations. the survey rig had no effecton the aerodynamic data. However, when the surveyrig was used for niaking wake velocity surveys behindthe right wing at z/s = 1. it caused an upwashof greater tha n 0.6 across the right wing and anincreased CL. The effect of the survey rig on thewake velocity data at this station was negated for themost part by making a reduction in Q to maintainCL = 0.6. This reduction left a small swirl in thewake iridiiced by the higher loading on the right wingof the VTW.

Span load data. Wind tiinnel pressure distri-h i t oii incwurcrrirnts on all VTW configurations in-dic*;ittda wing ccnt erline span load asynimetry. Asiiiiill lateral flow angularity toward the left wingcii1ised the ceiitcrhody to block the flow on the lowersurface of the wing just left of centerline and therebyr c d ~ i c e d e at y/s = -0.0612. Negligible rolling nio-iiiciit on tho VTW indicated tha t the span load effectwas localized just left of centerline. For this reason,the cp data at y/s = -0.0612 were ignored in eval-uating ( L .~ , S , ro.b/2, and d . (The determinationof thcsc valurs from the span load data is given inappcwdix A , )

Whorl the lift of thc centerbody was takcii intoaccount iritcgriitions of wing lift from the pressure(list rihitioii da ta agrcwl well with t h e lift nieasiircdcod( . W i t s iisccl t o iipproximitc the ccnt crbody lift.Siiiw t l i c distri1)iit on of lift on tlie centerbody wasi i i ikr iowii . its c4 ec t o i l S , IoTb / 2 , arid 2 s notiiicluclt.cl.

b y t 1 1 ~or(.( )iilitiic(. A pot(1it id-flow 1)iiIicl niet hod

Trailing- wing rolling-moment da ta. Averagedtrailing-wing rolling-moincnt data were significantlyirifliieiiccd b y vortex Irieandcr in both test facilities.In thc wind t i i n r i d , vortex rneander increased froman miplitiidt of about 0.02s at z /s = 1 to about0.2,s at z / s = 11. In th e water tank, meander ampli-tiidr Yitiigd from ricgligible at z/s = I1 to at least0 . 1 3 s at T / S = 70. As a rcwilt of this meander, the1nodcl was not cciitorcd steadily in tlie vortex, aridthus (~.Av ata falsely indicated rapid vortex decayw i t h downst rcaiii distance becausc thc long averagingpc.riod atrid incrvasing meandcr effectively enlargedt lic spatial averaging x o ~ i e . In both test facilities,t l iv iIi(~iiii(l(~rrnplificat on was well beyolid t ha t ex-pwttd i i i c a l ~ r i iir . possibly because of arnbient tur-I)iilrtico or the. cwlosiitg walls of each test facility.( SW itI)~)(iitlix3 for ii clisciissioii of the rricaiidcr am-I)lificitt i o i i . ) llio clioico of ;t shortc r avrragiiig periodw a s t 1111so i i t irvly itrl)it ritry sin(-r thc . averagc (,l,TWworil(1 (*orr($l i i t1 wit Ii fiill-scalt~ oll iipsct only iiiiclcrsi1iiiliit. ~ t i ( w i ( l w wiiclit ioiis.

To illustrate the length of t he rolling-moment av-eraging periods, the water tank and wind tunnel av-eraging periods can be scaled such that the VTWrepresents a full-scale transport airplane. Doing soyields full-scale periods of 18 and 64 sec, respec-tively. A comparison of these averaging periods withthe typical 1- to 3-sec period of a vortex encountershows that the experimental averaging periods arefar from characteristic aircraft roll response times.In comparison, the peak rolling-moment data con-tained fluctuations with a period analogous to about0.05 sec at full scale. Thus, C l , p ~an be expectedto provide a better nieasure than c i , A V of the poten-tial roll upsc.t for calni-air conditions. Because th epredominant rriearidcr period was long (equivalent tothe Crow instability period in the water tank), therelatively short response time for CL,PKat a allowedconsistent C l , p K values to be obtained for a giventangential velocity profile regardless of meander level.Thereforc, C l , p ~at a (where available) will be usedover C l , ~ v at a in evaluating attainment of down-stream alleviation by a VTW configuration.

Wake velocity data. Several factors influencedthe accuracy and applicability of the wake veloc-ity dat a measured in the wind tunnel . Two factorswhich affected the measured velocity near the vortexcore werr oscillations of the hot-film probe and vor-tcx meander. Probe oscillation effects were negatedby the 100 point per 0.02s spatial averaging tech-ni qw applied to the data ; however, vortex meandereffectively increased the spatial averaging of the ve-locity and vorticity profiles. Because vortex meanderincreased with downstream distance, the measuredvorticity profiles at both z /s = 6 and z /s = 11 weresignificantly reduced and distorted. Thus, as it didfor averaged trailing-wing rolling-moment data, mc-ander amplification caused the wake velocity dat a tofalsely portray rapid vortex decay with downstreamdistance. Another factor tha t influenced the accu-racy of the complete cross pl an t of velocity dat a wasa right-to-lcft wing flow angularity which caused thcvertical VTW mounting blade to shed its own wakeinto the cross plane beyond z/s = 1. In view ofthese contaminations, the wake velocity data wcrequantitatively accurate within 10 to 20 percent onlya t x / s = 1. At z / s = 6 and 11, these data mustbo taken as qualitative arid were useful primarily injudging whether complete merger of niult iple vorticeswithiii the wake had occurred.

Predicted and Measured Vortex WakeDevelopmentThis discussioii addresses corrrlat io i i of t hc. VTWspan load with vortex wilkr devc+q)iiient.

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Comparisons of the measured vorticity dat a and pre-dicted vorticity distributions based on both measuredand predicted span loads are made at x/s = 1 . Oneobjective is to determine if wake development can becharacterized accurately using relatively simple tech-niques to predict span load distribution and vortexwake roll up. A second, more specific objective is toevaluate the degree of similarity between wind tun-nel and water tank VTW configurations chosen tomatch the span load of VTW7So (the configurationutilizing spoilers for downstream wake alleviation).

First, to establish that the vorticity measure-ments at x / s = 1 were in correspondence with thespan load measurements and t ha t significant contam-ination had not yet resulted from wind tunnel flowasymmetries, a vortex blob code was utilized to pre-dict wake development with the measured span loadas input. The vortex blob technique is discussed indetail by Leonard in reference 29 . As an initial condi-tion for the blob code. the wing vorticity distributionwas derived in a manner similar to tha t of Westonand Liu (ref. 30) by discretization of the measuredspan load distribution into 50 equally spaced Gaus-sian vortices, each having a constant vorticity dis-persion radius p. The thickness of the shed vorticitysheet was then proportional to p, which was foundto best represent the velocity data for all VTW con-figurations when set to 0.0185s. As expected, thi svalue was very near the wake averaging length, orthe resolution limit of the data set.As the vortex blob technique is essentially in-viscid, it cannot be applied to model the wake ofVTW7So hecause of the turbulent and separatedflow caused by the spoilers. Of the three remain-ing VTW configurations having measured wake ve-locity, VTW7S3 had the most complex wake. Th ecomputation of its wake development based on themeasured span load is compared with the measuredvorticity field at x / s = 1 in figure 8. Although th einviscid nature of the roll up for the unseparated-flowVTW configurations may be considered dominant u pto x/s = 11, comparisons of predicted and measuredwake vorticity beyond z/s= 1 are pointless becauseof the unsteady nature of the flow field and the re-sultant effects on the measurements.The prediction shown in figure 8(b) matches themeasured data well in terms of the distribution ofthe residual vorticity sheet and the strengths andpositions of the dominant vortices. Note that theinboard region of negative (opposite sign) vorticityis predicted from the asymmetric loading measuredat wing centerline. This region is predicted as moreextensive than measured because the centerline Cewas taken as th e average of measured values on eitherside of the center. A more realistic result of the

lateral-flow angularity would be to reduce the liftacross the centerline only near the centerbody ( y / s


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velocity survey was made behind V T W 2 , which isincludcd in the comparison because it exhibited thesharpest span load gradients of all the VTW config-urat ions t e s t e d . In the figure, measured d c e / d ( y / s )values wcrc derived from linear point-to-point spanload slopes arid assigned at t h e midpoints of 9-stationda ta pairs. whereas predicted dca/d(y / s ) values wereoutput from a 51-point (equally spaced) cubic splinefi t to the lattice span load prediction at 42 equallyspaced sciiiispari positions.

It cipp(wh fro111figurr I) that the lattice tcch-tiiqiic is ca1)al)l(> f providing a realistic assessmentof s1);tIiwiw vorticity distri1)iition at tho wing trailingc~ lgo .As would bo cxpcct c d , tlic largest discrcpan-ties oc c * i i r r c ~ ltt t 1ic high-gradient regions of the spanload. Tlicsv cliscwpaticics arc probably at tributablcto t 11c truly t lirc~c~-diiiic~risioiialature of wing flowatid tliiis of sp;tti loitd dtvc~loprnrlit. The obviouslyt l i r (~c~-clir i ic~risioii~ilI)it11 load discontinuity causedby t l i r i wing-tip vortcx for V T W 2 is, of course, iiotprcvlictcd b y thc l i i t t icr technique. A question re-niairis a s t o wlict hw t l i t ~ypes of discrepancies arcsignificaiit whcn witkt iriitiatiori is computed with asI) i t t ial r(\sOlut oii 011 the. ordc r of 0.02s, t h r witkc itv-eritgiiig lmgtli.

Thc lat iw preclict ioiis waliiat od i i i f i g i i r ~ woreut i l i m l wit 11 thc. vortcx blot) t(~clitiiqii(~o prcdictV T W 7 . ; t i id VTW7S:$. T l i ~ s ~csiilts ar c ~ o ~ ~ i p i t r dwit I1 t 1 1 ~ 1 0 1(I\l)oii(liiigvorticity t i ~ ~ ~ i t s i ~ r ~ ~ t i i ~ ~ t i t sr i fig-i i t x I O . Tli(~ vc3r;tll cliitrwtci tt ioii of witkc dcv~l-o p t i i c t i t . iiicslucliiig vorticity distriht on itrld iriagiii-t i i c l r , is h w i i to be very g o o d . Even t h c riiultipleco i ic r i i t ritt ions of vorticity, which arc bclicvcd t o bediic t o tho 1 wing scgincrit twist c1iscoritinuitic.s oftlw VTW4 csorifigiiratioti.arc prctlictcd well. Thesecomparisons are niciiriingful only at an d abovc thespatial rcsolut ion limit of the da ta , which was de -t crtniiicd by t lie 100-point averaging technique andt hr spat ia1 itv(~rttgi1lg aused by vortex rricandcr. AtS / S = 1, thcsc. conibiiicd effects prodi ictd a spatialrosoliit iori l i i r i i t of about 0.02s to 0.04s. At scalessiiiiillcr t l i i t1l this, t lie vortcx blob prcdic*tioti s artifi-cially forc~do iiiatch the avcngcd vorticity field byt h c . clioicc of it vorticity shw t tliickrwss parameterthat is proport ioriitl t o thc spatial averaging lengthof t lit. (~xp(~riiiioiit1 ~~~e asiir e~~ie iits.

Tlici witicl tuiiiic.1 and wator tank tests each uti-l i m l VIW wifigiiratiotis t l l i t t werc twisted slightly( l i f f c ~ t s t i t ly i i i i t t t c i i i p t > to m t t c l i thv cxpcvt(v1spa11t i t i i v 01 t l i o t w t > t i ( w s h i t ; t t ( v l t l i c w approxiit1:Lt iorls; t t i ( I t x ~ ~ i i l t ~ v lt i VIW7S2 I)c411g tcist(d i l l t l w wtttcrt i t ~ ~ kt i i c l VIW~SI( i r i g tcstwl i l l t l i c i witid t i i r i r i c~ l .Of t l i ( w t l i t ( ~ 1 wiifigiirat ioiis. spa11 load t1ioas1irc-

t 11( vert (X witkt d(~v(~lo1)lil(~lito S / S = I for VTW4,

l o < t ~ l VIL27So. l t i ( ~ o i t I l ) I ( ~ t ( ~l ) i t i i lo;t(l dttt:t itt the

ments were obtained only on VTW7So and VTW7S3.As shown in figure 11, the differences between thethree configurations in ternis of their measured andexpected vorticity distributions at the wing trailingedge are minor.

Effects of Continuous Span LoadDistributionsAerodynamic data. Figlire 12 compares the aero-dynamic data of V T W configurations in group I-continuous span load distributions. All four config-

urations w ( w bclow stall at the CL = 0.6 test con-dition, arid interest itigly, considering the wide vari-ation in span loads t)ctwtwi th e configurations, allexhibited about the same measured drag level atC?L = 0.6. This result was verified in the water tank(see tablc V I I ) , whcrc V T W l (the untwisted wing)and V T W 4 (the tapered span load configuration) hadessentially idmt ical CD nieasiireinciits at CL= 0.6.

Span load data. A s c;tn be seen in figure 13,the vortc.x-lattice-predicted span loads compare fa-vorably with the nieasured span loads, with rna-jo r discropancics occurring only at the wing tip ofV T W l , V T W 2, and VTW3, and the wing center-line of V T W 4 . Vortex lattice underprediction a t thewing tip WBS caiisccl by the rapid roll up and passageof thc tip vortcx over the aft portion of the wingtip. Exaniiiiat ion of the most outboard chordwise c pdata (ref. 28) showed that the wing-tip vortex influ-enced thc last half of the wing chord. Over predic-tion at the wing centerline of VTW4 was probablydue to ceritort)ody influence at t h e high angle of at-tack of this configuration. Because V T W 4 had thelargest negative discrepancy between measured CI,and C L , ~table V) and because the lattice predic-tion was quite good for y/s 2 0.2, the actual inboardspan load was probably greater than that shown be -caiisc of iiriaccouritcd-for chordwise pressure forcesarid ceritcirbotly lift.

Two of these configurations, V T W I and VTW4,were investigated in thc water tank tmt. The rriajordifferences in their span loads can be noted in fig-ure 13 and table VI. Essentially, V T W l representsa span load which is between elliptic and rectangu-lar distributions, whereas the VTW4 span load liesnear a parabolic distribution in t e r m of its 6/2 aridro, ut has approxiniately liiiear regions of span loadsimilar to those foiiiid with triangular loaditig. To-t a1 aiigiilar Inonicnt uiri shed i r i t o t l l ~t>ltlispiirlwitkc>,as cktcrriiiiicd by ro3 as considerihly greater forV T W 4 . Howcwr, the distributioll of this IIIOI~ICIItiini. indicate(I t)y d . sliould 1)e s1iI)st itlit i d l y lriorediffused in the fully rolled-up wake. A s expected,

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the centroidal lift position S was about 13 percentless for VTW4 than for VTWl and indicated a cor-responding drop in wing root bending moment.

Trailing- wing rolling-moment dat a. As shown infigure 14, the tapered span load of VTW4 presents asignificantly reduced rolling moment to a small trail-ing wing when compared with the untwisted VTWlconfiguration. Peak rolling-moment data in the wakeof VTW4 exhibit a nearly level trend. whereas Cl,pKdata for VTWl decay slowly from 48 to 38 percentabove those of VTW4 from z/s = 11 to z/s = 70.Thus the vorticity dispersion in the wake, ratherthan the total circulation, was the dominant param-eter in characterizing the roll upset potential for asmall wing. This result is reasonable considering th atthe smallest vorticity dispersion radius for any VTWspan load was comparable to the trailing-wing semi-span. Vorticity dispersion is not strictly an invariantof the wake (ref. 11); indeed, the slow Cl,pK decayfor VT Wl is indicative of an increasing vorticity dis-persion radius with downstream distance. However,for the span loads of group I the vorticity dispersionradius can be expected to accurately depict vorticitydistribution following initial roll up. In fact, the cor-relation between C1,pK and dispersion holds up overthe small downstream distances in the wind tunnelfor all four VTW configurations, a fact not necessar-ily expected for C~,AVeasurements as the meanderamplitudes approach dispersion radii levels.

Comparing Cl,pK and c l , A V da ta merely substan-tiates that c l . A v dat a are unreliable as a measure ofrolling moment. This unreliability is especially no-ticeable in the wake of VTW4. where c [ , A V drops60 percent while Cl,pK remains essentially constantover 115 x / s 5 70. Comparing the wind tunnel aridwater tank c l , A v data at x / s = 11 again points outthe higher meander level, and thus lower c l , A V mea-surements, in the wind tunnel at this downstreamdistance.

This group of configurations illustrates the signif-icant wake alleviation attainable through span loadalteration alone. A comparison of the VTWl andVTW4 configurations shows that VTW4 achieveda 27-percent reduction in Cl,pK at z/s = 70 whilemaintaining essentially identical drag and reducingthe wing root bending moment by 13 percent. In thiscase, C1,pK was reduced on th e small trailing wing bymore uniform vorticity shedding at the VTW trailingedge. This more uniform shedding resulted in greatervorticity dispersion in the developed wake. The limit-ing case for this type of wake roll up with simple spanloads is triangular loading. (See table VI(b) .) Al-though the vorticity dispersion for VTWl was tighterthan that for an elliptical span load, it was probablynot unlike the dispersion local to vortices originating

at the discontinuous, high-lift flap systems of mod-ern jet transport aircraft. Thus, a significant level ofwake alleviation for small encountering aircraft ap-pears possible on future air transport aircraft if thespan load is tailored to increase vorticity dispersionin the wake.

Increasing the vorticity dispersion radius in thewake through this type of span load alteration in-curs a significant increase in total angular momen-tum (i.e., I shed into the semispan wake, and thusimplies an increased roll upset threat to encounter-ing aircraft with semispans much larger than the vor-tex generator vorticity dispersion radius d. Althoughit is true that C~,TWor a relatively large vortex-encountering airplane will theoretically increase di-rectly with vortex generator To , the corollary thatthe upset will increase correspondingly is not well es-tablished. Since it is not within the scope of thisreport to address vortex hazard correlation, it mustsuffice to state that because the inertia and energyrelationships between a small aircraft intercepting alarge aircraft's wake and a medium-size aircraft inter-cepting a large aircraft's wake are entirely different,it may be expected that the dynamic interaction be-tween the wake and the encountering aircraft may besignificantly different.

Wake velocity data. Figures 15 and 16 displaythe wake survey data for VTW4 as vorticity contourmaps at the three wind tunnel downstream measure-ment cross planes and as averaged u and w velocityprofiles through localized vorticity concentrations atx/s = 1. Roll up is seen to proceed from a sheetat L / S = 1 (fig. 15(.)) with several vorticity cnncen-trations due t o the 1' increments in wing twist to asemispan wake at x / s = 11 (fig. 15(c))with its domi-nant vortex outboard and a residual vorticity concen-trat ion inboard. Velocity profiles a t z/s = 1 portrayrelatively tight vortices with axial flow deficits. Tur-bulence levels, inferred by cw and uu (fig. 16). areseen to be negligible outside vortex cores, whereasthe high peaks a t the cores result from the combinedeffects of the high-level velocity gradient, hot-filmprobe'oscillation. and vortex meander. A s noted pre-viously, the inboard negative vorticity at x / s = 1 waspossibly due to the centerline wing lift asymmetry,whereas the positive vorticity on the centerline is be-lieved to be shed from both the VTW blade support,under the influence of the lateral flow angularity, andthe VTW centerbody.

Effects of Partial-Span-Flap Span LoadDistributionsAerodynamic data. Figure 17 compares the aero-dynamic data of the three VTW configurations that

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simulate flapped-wing span loads by outboard wingtwist and effectively model 40-, 60-, and 80-percentflapped wings. Each configuration exhibited thesaiiie lift curve slope and avoided wing stall until be-yond the CL = 0.6 test condition. Stall occurred atthe lowest angle of attack for VTW6 because i ts localangle of attack (a+Aa)at the wing tip was 2' and 3higher than those of VTW7 and VTW5, respectively.Sincc t h e outboard wing panel stalled first, the con-figuration with the least outboard twisted wing area,VTW7, had the highest


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reduction in both lift curve slope and maximum liftcapability with a substantial increase in drag for aspecified lift. As listed in table VII, at CL= 0.6 theCD increased from VTW7 to VTW7So by 0.056 inthe wind tunnel and 0.066 in the water tank . Thedrag for VTW7So is thus about 190 percent greaterthan that for VTW7.

The VTW7So span load was matched by wingtwist alone with the VTW7S1, VTW7S2, andVTW 7S3 configurations. Aerodynamic data forthese configurations are presented in figure 22(b).Because these configurations matched span loadwithout the addition of splines or drag plates, theCD increase referenced against that of VTW7 wastypically 0.01 or less at CL= 0.6 and yielded an in-crease of about 30 percent in total drag. The effecton the aerodynamic dat a of V T W7S P caused by in-stallation of the drag plates on VTW7S3 is shown infigure 22(c). The drag plates were sized to increasethe VTW7S3 drag to near that of VTW7So. An ex-tra CD increase of 0.044 resulted, for a total dragincrease of 170 percent relative to that of VTW7.

Two water-tank-tested VTW configurations usedsplines sized to produce a drag increase equivalent tothat caused by the spoilers with the VTW a t zero lift .(This drag increase was smaller than tha t producedby the drag plates.) Splines were added to the twistdistribution of VTW7 to produce VTW7X. The GDwas thus increased by 0.027 at CL = 0.6 to producean increase in drag of about 90 percent relative tothat of VTW7. Splines were added to the twistdistribiition ofVTW7S2 o produce VTW7S2X. Thisaddition increased CD by 0.026 and resulted in atotal C:D increase of 110 percerit over that of VTW7.Since no increase in angle of at tack was required tomaintain CL = 0.6 with the splines, it is surmisedthat they were sufficiently aft of the VTW trailingedge and aligned with the flow that they did notsignificantly alter the VTW span load near CL= 0.6.

Span load da ta. Figure 23(a) shows the span loadda ta for VTW7So and illustrates the effect of spoilerson VTW7. The ce was essentially halved a t y/s = 0.6because of the spoiler installation. This decreaseforced an increase in ro o maintain CL = 0.6 anda corresponding decrease in b/2 to maintain the netimpulse (6/2)r0. Notice that the loading around thewing ti p was increased slightly because of the higherangle of attack required t o maintain CL= 0.6. Thisincrease suggests that the wing-tip vortex should, atleast initially, be more intense for VTW7So than forVTW7. Not only did ro ncrease and b/2 decrease by19 percent, as shown in table VI(a), but the vorticitydispersion radius was also more than doubled in thetransformation of VTW7 to VTW7So.

Figures 23(b), (c), and (d) present the mea-sured and/or predicted span loads of VTW config-urations that utilized wing twist alone to match theVTW7So measured span load. Other than a failureof VTW7S2 and VTW7S3 to duplicate the outboardside of the spoiler ce trough, these span loads ap-proximate the VTW7So span load well and match i tsdominant wake initiation parameters ro, /2 , and dwithin 2.5 percent.The addition of drag plates to VTW7S3 requiredan extra 0.3 LY to maintain CL= 0.6 and thus moresubstantially altered the VTW7S3P span load fromthat of VTW7S0, as seen in figure 23(e). In thiscase, values given in table VI(a) for roand b/2 varied4 percent from those of VTW7So. Figures 23(f) and(g) portray the expected span loads for VTW7SGand VTW7X, respectively, assuming the splines donot influence their span loads. Measured span loaddata are not available, since neither configurationwas evaluated in the wind tunnel.

Trailing-wing rolling-moment d ata . Figure 24(a)establishes the downstream C ~ , T W eduction accom-plished by the addition of spoilers to the 80-percentflapped-wing configuration. In terms of C 1 , p K mea-surements, a 31-percent reduction was achieved byx / s = 70. These results are consistent with c l , A Vmeasurements obtained over shorter downstream dis-tances by Croom (ref. 33). Note that the alleviatedconfiguration. VTW7S0, initially had higher C~,TWda ta in both facilities ( as expected based on the spanload measurements), but the crossover of C~,AVe-tween VTW7So and VTW7 in the wind tunnel over6 < z/f < 11 did not occur in the water tank foreither C 1 , p K or C/,AV ntil 11 < x / s < 40 . Thisdifference is an indicat ion of the possible effect thatvariations in turbulence and meander levels betweenfacilities can have on c l , A V data.

Figure 24(b) shows the effect on downstream wakealleviation caused by matching the span load ofVTW7So without the high drag and turbulence ofthe spoilers. The C l , p K data for VTW7S2 indicatethat the multiple vortex wake structure that now ex-ists ( in place of the predominant single semispan vor-tex of VTW7So) proceeds to x / s = 70 without com-plete merger. Since the wing-tip vortex of VTW7Sois well away from the spoiler region, it would be ex-pected tha t the wing-tip vortices of VTW7So andVTW7S2 would initially be equivalent. This expec-tation is verified by the C l , p K data at x / s = 11.Thefact that the inboard vortex (originating from theinboard por tion of the semispan) of VTW7S2 alsoinitiates with an identical C l , p ~trength was fortu-itous. By x / s = 70, the predominant outboard vor-tex of VTW7S2 was registering an 11percent C l , p K

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reduction relative to that of V T W 7 , or about one-third of the alleviation obtained with the spoilers.This small reduction of the wing-tip vortex inten-sity relative to that of V T W 7 may be due to slightlyhigher vorticity diffusion created by the turbulencefrom the mutually shearing vortices in the niultiple-vort ex wake.

Figure 24(c) compares the C~,TWata for thebaseline urialleviated and alleviated configurations( V T W 7 and VTW7So) with those obtained for V T Wcorifigiiratioris using the splines or drag plates to sini-ulate the drag and tiirbiilence effects of the spoilers.T hc addition of sp1iric.s to VTW7S2 (configurationVTW7S2X) produced, at the initial downstream lo-ciitioii, ( ' l ,pK data for both the inboard and out-board vort iws t h i t wcre below C i , p ~ ata for ei-thcr VTW7So or VTW7. The wake of VTW7S2Xcoritiiiiied to decay until about z /s = 40, and bys/s= 70 there was no discernible inboard vortex andthe. ("1,pK was slightly lower than that obtained forVTW7So. Thiis, the splines in corijiinction with theniatclicd spar1 load appear to have created a dowii-st reairi wake siiriilar to that of the spoiler-alleviatedconfiguration. T h e lower incromerital drag and tiir-bulencc of the splincs may account for the longertiiiic rcquircd for thc drcay of the. int)oarcl vortex sys-t c i i i . 1)rc.aiiscthe rcrririarits of this system niay havc.riicrgcd iiito thv cornplct 1 vortex systcmi to yield no('1.pK dccay along 4 0 < s /s < 70 . Ai1 exarriiiia-t ion o f rc.lativc vortox 1)ositioiis withiii the wakcs ofVTW7Sz aiicl VTW7SzX shows t hc iucrcasetl like-lilioocl o f i i i c ~ gc r . f tlic VTW7S2X inboard vortexsiiico. by s/s= 40. the displaccrriciit ht wc wi t h t in-board aiid wing-t ip vortices for V T W 7 S G was abouthalf that for VTW7S2. Dccay rates twyoiid x / s = 70arc iiiikriowri; however, tlic equivalence of both (>l,pKand C~.AVata between VTW7So and VTW7S2Xwould r c~p i rc omparable rneaiidrr levels and, there-fore. siiiiilar turbulciic.~~evels in each wake.

Since. thci iiicrcriicntal drag and turbulence plusspan load rniitchirig of VTW7S2X replicated thedowiistrcani wake dlrviation of VTW7So (the80-perw1it flapped wiiig with spoilers), whereas theVTW 7Sz configuration (which used wing twist aloneto r i iatch the VTW7So span load) achieved littledowiist rcam allcviat ion, how important a role wasspaii load playirig in tlic spoilcr-at aiiied alleviation?To clctcririiiie if t h c . iiicreirimt a1 drag arid tiirbiilcncco f tlic spoilcrs w ( w thc. kry paramcttm in the al-lcviat i o i i obt itiiicd with thci VTW7So corifigiiration,( ' 1 . p ~ ata w ( w t akci i i n tlic wakc of VTW7X. This('oiifigliriitio n c-orisistY I of t 1 1 ~)iis(.liii(>unalleviattdV T W7 (8O-p(~c(~itl;tppccl w i n g ) with splines addedto s i i i i i i l ; i t (> oiily t ti c clr:tg t i i i ( 1 tur1)iilciicc effects oft l i ~poilvr5. Ih~ i i (~ f i ( ' i idwl)(l( ' t of' t h o VTW7X coil-

figuration were its lower drag and I As shown infigure 24(c ) . V T W7 X did indeed produce substantialwake alleviation; C1,pK data essentially agreed withthose for the predominant vortex of V T W 7 S S and,throughout the z/s range, remained below those ofVTW7So.

Wake velocity data. Figures 25 and 26 presentthe measured vorticity cross planes and selected ve-locity profiles in the wake of the spoiler-alleviatedconfiguration, VTW7So. When these measurementsare cornpared with the corresponding da ta for V T W 7(figs. 20 arid 2 1 ) , the effect of the spoilers is appar-ent. A s predicted by the higher wing-tip span loadof VTW7So (caused by the increased a to maintainCL= 0.6) and by C l , p ~ easurements, the wing-tipvortex of VTW7So w as initially more intense thanthat of VTW7. This effect is most noticeable whencomparing velocity profiles of the tw o Configurationsat z /s = 1 (figs. 21(t)) and 26(b)). Additionally, theintensity of the VTW7So flap vortex was reduced be-cause the local reduction in span load caused by thespoiler lowered the amount of vorticity wrapping intoit . As a resnlt, by z/s = 6 the VTW7So wing-tip vor-tex predominated, whereas the V T W 7 wake was stillin the midst of a merger of the flap and wing-tip vor-tices. Bcyontl z/s = 11, the merger of the V T W 7wake system was completed, and a stable, plateauphase, as dctrrinincd by the C l , p ~ata , resulted un-til at least T / S = 70. However, the wake of VTW7Sodecayed significantly beyond z / s = 6 as the effect ofthe spoilers on wake development w as incurred.T h e substantial drag and turbulence associatedwith the spoilers were manifested in the wake in sev-eral ways. Most obvious was the broad region ofunsteady flow aft of the spoiler location, as cxernpli-fietl by the high ( T ~nd 0, measurements at z / s = 1(fig. 26(d)). This turbulence field shows up in thcz / s = 1 vorticity plane as very diffused and spreadregions of positive and negative vorticity cnianatingfrom either side of t he spoiler-induced ce trough. Thediffused characterization of these regions was par-tially a result of the increased spatial averaging pro-duced by the highly unsteady nature of the flow fieldhere. Apparent also in figure 26(d) is the substantialaxial velocity (u) eficit created downstream of thespoilers. This velocity deficit is representative of theunfavorable pressure gradient produced by the highdrag of the spoilers.

Thus, the spoilers introduced three basic Inecha-nisrris capable of contr ibut iiig t o t h e sigiiificwit decayof the VTW7So wake beyond z /s 5 6. Bcsidcs thechange in span load, two direct in pl ts of tlic spoil-ers were high turbulence, which incrc3ascd hc ot 1ic.r-wise laminar rat e of vorticity diffiisioii, and increased

14


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drag, which caused a positive axial pressure gradientthat tended to counteract the convective concentra-tion of the vorticity sheet. The role of span load alter-ation in the downstream alleviation of VTW7So ap-pears minimal, as is demonstrated by comparing thetrailing-wing measurements behind VTW7S2 (whichsimulated only the span load alteration of the spoil-ers) and those behind VTW7X (which simulated onlythe incremental drag and turbulence of t he spoilers).

In marked contrast to the highly diffused vorticityconcentrations aft of the spoilers on VTW7S0, highlyconcentrated vortices were created from both sidesof the ce trough on VTW7S3. (See figs. 27 and 28.)These vortices were produced by wing twist alone.As was noted with the water tank trailing-wing datathrough x / s = 70 and suggested in the wind tunnelby the enlarging displacement between vortices withincreasing z/s, this multiple vortex wake persistedfar downstream. The similarity between VTW7Soand VTW7S3 wing-tip and residual flap vortices atz/s = 1 and the similarity of their combination atx / s = 6 mean that the spoiler wake has as yethad little effect on this portion of the VTW7Sovortex system. This is in good agreement withidentical C ~ ,PKeasurements for both VTW7So andthe wing-tip vortex of VTW7S2 at z/s = 11 inthe water tank. A significant decay then ensuesin the wake of VTW7S0, apparently as a result ofthe spoiler wake and the wing-tip vortex wrappingtogether. Once this occurs, the turbulence and axialdeficit imparted to the flow field by the spoiler act todissipatr the wing-tip vortex system.

The addition of splines to VTW7S2 (creatingv-"w-7$ - -L. 2xj produced a near-field reduction i r i C~,PKnic"asureriit~rif for both the wing-tip and inboard vor-

tex systems. This effect is similar to the c l , A V reduc-tion between the wakes of VTW7S3 and VTW7S3Pthat was caused by installa tion of the drag plates.Whether this reduction resulted from a more rapidinitial decay due to turbulent diffusion of vorticity orfrom an impaired concentration of the vorticity sheetbecause of th e added drag is unknown. However, theeffect w as clearly independent of the inboard vortexsystem since the wing-tip vortex C1,pK data essen-tially matched for both configurations with splines-VTW7X, which produced only an outboard vortexsystem, and VTW7S2X, which produced both an in-board and an outboard vortex system.

Thus, the downstream wake alleviation attainedby VTW7So resulted directly from the incrementaldrag and turbulence associated with the spoilers.The span load alteration caused by the spoilers isseen to play no part in the development of thealleviation for this particular configuration.

Concluding RemarksSeveral measurement techniques in two different

test facilities were used to provide a comprehensiveand interrelated set of wing and wake measurementsin the variable twist wing investigation. Detailedwing and near-wake data were obtained in a windtunnel, and trailing-wing surveys of the near- and far-downstream wake were obtained in a water tank. Atotal of 14 different wing configurations were testedat the same Reynolds number and lift coefficient ineach facility.

The variety of measurements allowed results tobe correlated and their accuracy to be checked be-tween test facilities as well as between wing andwake measurements. As a result of these correla-tions, several facility and measurement technique ef-fects were found t o have significantly influenced por-tions of either the vortex wake roll up or the exper-imental quantification of vortex wake intensity. De-tailed wind tunnel measurements of both span loaddistributions on the wing and cross plane wake ve-locities at a semispan downstream correlated wellwith each other and with water tank measurements ofpeak trailing-wing rolling moments. These detailedmeasurements were used to show that inviscid an-alytical prediction techniques accurately portrayedthe vortex generator span load distribution and ini-tial vortex wake development to the resolution limitsof the da ta . However, meander and flow angular-ity in the wind tunnel prevented. in other than aquali tative sense, the use of wake velocity data mea-s u e d at C; a i d 11 stmispans downstream. Averagetrailing-wing rolling moments were shown to be un-reliable as a measure of the vortex intensity becausevortex meander amplification did not scale betweenthe test facilities and free-air conditions. High val-ues of meander amplification caused average trailing-wing rolling-moment data in both facilities, as well aswake velocity data in the wind tunnel, to falsely in-dicate rapid vortex decay with downstream distance.

A tapered-span-load configuration, which exhib-ited little or no drag penalty, was shown to offersignificant downstream wake alleviation to a smalltrail ing wing. Thi s wing configuration achieved wakealleviation through span load specification of moreuniform vorticity shedding at the wing trailing edge.In contrast , the greater downstream wake alleviationachieved with the addition of spoilers to a flapped-wing configuration was shown to result directly fromthe high incremental drag and turbulence associatedwith the spoilers and not from the span load alter-ation they caused.

15


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TABLE I. PRESSURE ORIFICE LOCATIONS ON THE VARIABLE TWIST WING

~~ Span locations~Wing segment~

O-LU0-Ra13579131517

19212325272931333536

Y l S-0.0612.0612

.1560

.2037

.2513,2989.3465.4418.4894,5370.5846.6322.6798,7275,7751.8227.8703.9179.9656.9894

~-Chord locationx L E / c - -0 .0125,0250.0500.loo0.1500.2000.3000.4000.5000.6000.7000.8000.goo0.9800

f z / c_ _ 0 .01894.02615.03555.04683.05345.05738.06001.05803.05294,04563.03664.02623.01448.00403 -

aLeft (0 -L) and right (0-R) side of wing center-panel section.

16


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TABLE 11. VTW CONFIGURATIONS

GroupI Continuous span loaddistributions

I1 Partial-span-flap spanload distributions

I11 Alleviated vortexwake configurations

Wing twistconfigurationdesignat on

VTWlVTW2VTW3VTW4VTW5VTW6VTW7

VTW7SoVTW7S1

VTW7S3

VTW7S3PVTW 7S2X

VTW7X

Configuration descr iptionUntwisted wingApproximately rectangular loadingMaximum loading at midsemispanTapered loading, maximum a t centerline40-percent flapped wing60-percent flapped wing80-percent flapped wing80-percent flapped wing with spoilersWing twisted to approximately match

span load of VTW7So (version 1)Wing twisted to approximat,ely match

span load of VTW7So (version 2)Wing twisted to approximately match

span load of VTW7So (version 3)VTW7S3 with drag platesVTW7S2 with splinesVTW7 with splines

WindtunnelJJJJJJJJJJJJ

WatertankJ

J

JJ

J

JJ

17


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0 09 9f m mI Ir ( 4

0 0c?:d ? l3 I I

m u :,,,-I I0 )

0

0

C l e o t-0 ' I I I I

0

18


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a0 f

ao-0-1 'a' I f

a0 ' I f

-t-I f

0 f

_ _In="a

-e53an

19


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(4IIa0

4


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TABLE V. FORCE-BALANCE-ME.

Wing twistconfigurationVTWlVTW2VTW3VTW4VTW5VTW6VTW7VTW7SoVTW7S1VTW7S3VTW7S3P

SURED IFT , JD PRESSURE-INTEGRATED LIFT FOR A NOMINAL CL = 0.6

CL0.614

.601.602

.628

.615

.620

.596,591.607.583.606

CL,P0.580.575.592.577.597,591.571.555.575.564.591

w-0.055-.043-.017-.081-.029- 047- 042-.061-.Os3- 033-.025

C L , ~ CL,CB)- C1CL-0.030-.021.ooo

[email protected]+.015

21


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TABLE VI. TWO-DIMENSIONAL SPAN LOAD CHARACTERISTICS[C, = 0.61

Wing twist

VTWlVTW2VTW3VTW4VTW5VTWGVTW7VTW7SoVTW7S1VTW7S3VTW 7S3P

configuration

(a) VTW span loads

3-3 6%

0.448 0.0975.469 .0927.452 .0898.391 .123.386 .126.405 .110.417 .lo5.390 .125.389 .124.377 .128.375 .130

Span loaddistributionRectangularEllipticParabolicTriangular

b60.879.924

.954,695

.680

.780,815.687.691.670.658

- -3 & 6 30.500 0.0857 1 000 0

.424 .lo9 .785 .223

.375 .129 .667 .236

.333 .171 .500 .289

(b) Theoretical span loads

-3

0.12.11.22.24.26.16.12.25.25.24

22


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TABLE VII. TRAILING-WING AND CORRESPONDING VTW DATA[VTW C L = 0.61

J4 s Cl,PK0.021tunnelWater 7.5 0.037

cl , V0.07311.011.239.339.471.277.76.0

11.06.0

11.06.011.0

10.410.040.139.769.36.0I IVTW5 I Wind I 11.5 1 0.027

-.9460.878

.857

.837

.776

.796-0.972-1.018-0.856-.887

-0.847-.8200.776

.776

.490

.510

.714' -0.896

.0610.0

-.163-. 163- 306- 306

-0.014.005

0.115.005

0.128.088

0.061.061

-.327- 347- 8780.170-.162.1310.209-.036

.169- 0770.047

.05600

.082-.143- 408-.408

-.323

Trailing-wing p(

.0620.099 0.096

.054

.0270.077

.0640.065

.0520.057

.0440.067

0.059.065

.036.064 .023

0.055.050.0411 .047

0.050.044.040.046

0.040.046

0.0670.046

.041

.071 .044.070 .031

.092

.088

.~

X I S I Y l S6.0 I -0.910

VTW2VTW3VTW4

Wind 6.5 0.027tunnel 6.5 .027Wind 4.8 0.028tunnel 4.8 .028Wind 12.5 0.028tunnel 12.5 .028Water 12.6 0.037

ition I I

11.011.06.06.0

11.011.06.0

11.010.310.610.239.469.669.1

-.848-.479

-0.851- 684-.768-.844

-0.808- 8330.837

.827

.857

.714.714

.714

VTW6

VTW7

23

Wind 9.1I O TWind 8.5 0.030tunnel 8.5 .030Water 8.1 0.031


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TABLE VII. Concluded[VTW CL = 0.61

"

WingconfigurationVTW7So

"VTW7S3

VTW7S3PVTW7S2X

VTW7X

FacilityWindtunnelWatertank

Windt urlIlel

Windtunnel

Watertank

Windtunnel

WindtunnelWatertank

Watertank

~~ -

Trailing-wing px / s6.011.011.238.238.970.569.6

6.06.0

11.011.06.06.0

11.011.011.310.911.639.638.740.269.970.270.26.06.0

11.011.011.011.011.510.639.042.439.969.369.010.711.140.470.369.5

Y l S-0.888-.8270.714

.592

.571

.571

.571-0.397

-.846-.311- 933

-0.437-.856-.375-.9110.857.367

.388

.612

.633

.674

.388

.388.8160.830.379

.729

.3210.696.3960.918

.449

.592

.571

.939

.612

.6330.796

.776

.755

.694

.714

tion21s0.104

.lo30.082- 408- 388-.714-.714- 036.124

.045-0.037

.131-.202

.0870.082

-.301

-.225-.225-.204-.204-.898

-1.020-1.020- 6530.137-.013

.110-.2640.112-.2370.082- 204- 408-.408- 653- 653- 6530.061

.041-. 163- 367-.429

C1,PK

0.074.059.048

0.074.077.064.047.062.041

~~

0.059.040.044.021.044

0.061.047.045

cl ,AV0.049.035

0.055.034.017

0.073.056.075.044

0.072.055.061,041

0.062.060.019.025.010.013

0.057.086.048.077

0.048.024

0.014

.010

.0130.043

.027

.022


28/118


29/118

Circulation or lift distribution r'(y) -7

VTW

r Vortex f i 1 aments

y t i c a l velocitydistributionY

Downwash di

Vortic ity distribution

dy dz = JCrossplane pl anebounaar:/VT W -\\ / '\ /I

l/ Measurementcross plane

.dR7


30/118

aJtT,ldLLldV3:I->

*r

I -m *\\\\\

27


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1 l 1 1 1 1 11 1 1 1 1 I IIIIIIIII

v,

rua,L

Y

IIIIv)nStuv)n.7Em

IIIIIIIun-aL0-c0

IIII0c,ruLLW@-tuI

-r

w

EtuU0hN

.r

7n

c,Sa,a,6lm E

%32-auI].-3ubod0d

.339.e3-,'00E

28


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Dev ce

Spoi erSpl i eDrag plate

Spli ne detail vi ew I

Front faceposition, xLE/c

0 . 31 . 4 31 . 4 3

Figure 5. Installation of spoilers, splines, or drag plates a t y/s = h0.607 on VTW. Unless noted, all dimensionsare normalized by VTW semispan.

29


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V T W I

V TW2

V TW3

V T W 4

(a) Group I-continuous span load distributions.Figure 6. V T W groups.

30


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VTW7

L-84- 10.700(b) Group 11-partial-span-flap span load distributions.

Figure 6. Continued.

31


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V TW 7 S 0

VTW7SI

V T W 7 S 2

V T W 7 S 3

(c) Group 111-alleviated vortex wake configurations.Figure 6. Continued.

32


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V T W 7 S 2 X

V T W 7 X--

L-85-104(c) Concluded.

Figure 6. Concluded.

33


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34


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.2 I I I 1 I I0 . 2 .L i . 6 .8 1 . o i .2Y / S

(a) Initialization at z/s = 0 from span load measurements.

__ ns/~, = en/2

- . 2 I I I I I I0 .2 .L i . 6 . 8 1 . o 1 . 2Y/S

(b) Predicted vorticity at z /s = 1.

~ - -us o b

~._ _ -I:;.- -2 I I I I u.2 .Y .6 .8 1 . c 1 . 2Y / S(c) Measured vorticity at z/s = 1.

Figure 8. Predicted vorticity cross plane at x / s = 1 based on measured span load for VTW7S3. Measuredvorticity cross plane at z/s = 1 provided for comparison. Contours are labeled with the exponent n.

35


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100

-10dc i.do 20-30- 4 0

5

0dcJid(y/sJ -5

-1 0

I

I-0 Measured

- - P r e d i c t e dIL A- 2 .L f .6 .8 1 .0(a) VTW2.

0 Measured- P r e d i c t e d

0 .2 .L f .6 .8 1.0Y l S

(b) VTW4.

50

-5

-1 0-15

50

-5-1 0-1 5-20

0 easured- r e d i c t e d

i 1 1 i 10 .2 .Lf .6 .8 1 .O

(c) VTW7.

0 easured- P r e d i c t e d1

01 1 1 1 1

0 .2 .L f .6 .8 1 .OY l S

(d ) VTW7S3.

Figure 9. Vortex-lattice-predicted and span load measured d c d d ( y / s ) .


40/118

- s/~,=e"//2_ _ _ ns/U,=-e / 2 I n i t i a l i z a t i o n a t x / s = 0 f r o m s pan l o a d p r e d i c t i o nn

P r e d ic te d v o r t i c i t y a t x / s = 1

.2r M easured v o r t i c i t y a t x / s = 1

- .2 1 I I I I I0 .2 . Y .6 .8 1 . o 1 . 2Y / S

(a ) VT W 4 .Figure 10. Predicted vorticity cross plane at z / s = 1 based on predicted span load. Measured vorticity crossplane at x/s = 1 provided for comparison. Contours are labeled with the exponent n.

37


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m / U , = en//2ns/U, = -en//2 Initialization a t x / s = 0 from s pan load prediction

0 1

- . 2 1 I I I

.2r Predicted vorticity at x / s = 1

.2r Measured vorticity at x / s = 1

I I 1 - J I.2 .Y .6 .8 1 . o 1 . 2Y/S

- - 20

(b ) V T W 7 .Figure 10. Continued.

38


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. 2

z/s

- .2

- 2

- .2

.2

- - s/u, = en/2- - - fis/U, = -en/2 Initialization a t x / s = 0 from span load prediction

Predicted vorticity at x / s = 1

- Measured vorticity at x / s = 1

1 . 220 .2 .Y .6 .f3 1 . oY/S

(c) VTW7S3.Figure 10. Concluded.

39


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50

-5dcdo 10

-15-20

-0- VTW7S0 data---o---TW7S3 data

0 - 2 . Y .6 .8 1 .0Y s

(a) Measured d c e / d ( y / s ) for wind tunnel VTW configurations.

50

dcQd(y/sJ -10-15

-0

- 0 VTW7S0 data-VTW7S3 predictionVTW7S2 prediction- -- 0

-200 - 2 - Y .6 -8 1 . 0Y/S

(b) Measured d c p / d ( y / s ) for VTW7So and predicted d c p / d ( y / s ) for w i d tunnelcorifigiirat o 11 VTW7S3 and water t ank configuration VTW7S2.Figure 11. Values of d c e / d ( y / s ) for wind tunnel and water tank VTW configurations twisted to match thespan load of VTW7So.

40


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.3

.2

.1

0

1.2.6

0

-.6

-1.2 I-8 -4 0 4 8 12 1 6 20

deg

0 VTW10 VTW20 VTW3* VTW4

0 .1 .2C D

Figure 12. Aerodynamic data for V T W configurations in group I-continuous span load distributions.

41


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5

1 * o.8.6.Ll- 20

-5bI I 1 1 1-.2 0 .2 .Ll

Y l S.6 .8 1.0

-51.o-8

.20 1 I 1 I I I I I-.2 0 -LL - 6 .8 1 .0

2 .Figure 13 . Measured and vortex-lattice-predicted span loads for V T W configurations in group I-continuousspan load distributions.42


46/118

CR

-5 I= I I I I I I I I I

-.2 0

0-510

1.0- 8- 6* Y- 20

92Y / S

(c) VTW3.

- L f - 6 - 8 1 .0

-15 1 1 I 1 I I I 1 I

0 MeasuredPredicted

-.2 0 .2 .L fY/S

= 6 - 8 1 - 0

(d) VTW4.Figure 13. Concluded.

43


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Wind Watert u n n e l t a n kd 0 VTWld VTW2C I VTW3LY A VTW4

I ,AV

10- 0806

OLf02

01008.O601102

00 10 20 30 110 50 60 70 80

X / S

Figure 14. Trailing-wing rolling-moment data for V T W configurations in group I-continuous span loaddistributions.

44


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(a) z/s = 1.Figure 15. Normalized vorticity contours in semispan wake of VTW4. Contours are labeled with

the exponent n.

4 5


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.L&

.2

0

z / s

- 2

- 4

- . E

0A0 .2 .6 .8 1 . o

Y / S(b) Z/S = 6 .

Figure 15. Continued.

46


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0 .2 .6 .8 1 oY / S

(c) z/s = 11 .Figure 15. Concluded.

47


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- s/ l

I

3

1

.20 .2 . 6 - 8 1 . oY / S

(a) Normalized vorticity field showing spatial position of velocity profiles. Contours are labeled with theexponent n.

.3

.2Velocity .1r a t i o

0-.l- 2

-2

u,m 3 r s 2 r

Y I S Y I S(b ) Velocities along path A-A. (c) Velocities along p ath B-B.

Figure 16. Normalized vorticity contours an d vertical and axial velocity profiles for VTW4 a t Z/S = 1 .

48


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.3

.2CD

.1

0

1.2

.6

0

-.6

-1.2-8 -4 0 4 8 12 16 20

a , deg

0 VTW5VTW6

0 VTW7

0 .1 .2 .3CD

Figure 17. Aerodynamic da ta for V T W configurations in group 11-partial-span-flap span load distributions.

49


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1.0- 8

- 20

R

4 1 , ,-10

- . 2 0 .6 -8 1 .0

(a ) VTW5.

1 * u.8.6* L i.20

- . 2 0 - 6 .8 1 .0

(b) VTWG.Figure 18. Measured and vortex-lattice-predicted span loads for VTW configurations in group II-partial-span-flap span load distributions.50


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R

1 .o- 8- 6*Li- 20-02 0 .2 *Li .6 - 8 1 .0

Y / S

( c ) V T W 7 .Figure 18 . Concluded.

5 1


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1 ,P K

1 ,AV

100806OL l020

01008060q02

0

Wind Watertunnel tank

VTW 5d VTW60 0 V T W ~

0 10 20 30 LlO 50 60 70 80X I S

Figure 19. Trailing-wing rolling-moment data for V T W configurations in group 11--partial-span-flap span loaddistributions.

5 2


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- .2

- s/~,= en/2- _ _ ns/U,= -e / 2

I I I I 1

(a ) z/s = 1.Figure 20. Normalized vorticity contours in semispan wake of V T W 7 . Contours are labeled withthe exponent n.

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.2

0

.2

ns/Uw = e ' / ~ns/~, = -en//2

" .2

.2

0

U S

- .40

.L t

(b ) Z/ S = 6.

__ ns/uw = e n / 2- - - n s / U w = -en/2

0

.6Y / S

- 8 1 . o

0

I I 1.2 .Lt .6 .8 1 . o

Y / S

0epl - - - - - .

( c ) z / s = 11 .Figure 20. Concluded.

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.2

z / s

- .20 .2 .Y . 6 .8 1 . oY l S

(a) Normalized vorticity field showing spatial position of velocity profiles. Contours are labeled with theexponent n.

Vel ocr a t i o

- .2'.2 I. 3 -

UTS t a n d a r dd e v i a t o n -Urn

I

-80 -85 -90 -95 1.00 1-05 -60 -65 -70 -75 -80 -85Y I S Y I s

(b) Velocities along path A-A. ( c ) Velocities along path B-B.Figure 21 . Normalized vorticity contours and vertical and axial velocity profiles for VTW7 at z/s = 1.

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.3

.2

.1

0

1.2

6

-.6

-1.2-8 - 4 0 4 8 12 16 20

d e g

0 V T W 70 VTW7S, .1 .2CD

.3

(a) Baseline unalleviatcd VTW7 and spoiler-allcvi;ttcc1 VTW7So.Figure 22. Acrodynaniic data for VTW configiiratioiis i I i group I11 allcviatcd vortex wake configurations.

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.3

.2C D

.1

0

VTW7S,0 VTW7S,A VTW7S,0 VTW7S,

1.2-6

c L 0-. 6

-1.2-8 -4 0 4 8 12 16 20 0 .1 .2 .3

a , deg(b) VTW7So and configurations using

vortex wake alleviation prediction

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