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Tupolev 154M noise asesment ( -154)

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>Contents

1 TheNoiseProblem
2Effects ofNoise

2.1HearingLoss

2.2NoiseInterference

2.3 SleepDisturbance

2.4NoiseInfluence on Health

3NoiseSources

3.1JetNoise

3.2TurbomachineryNoise

4NoiseMeasurement andRules

4.1NoiseEffectiveness Forecast (>NEF)

4.2EffectivePerceivedNoiseLevel (>EPNL)

5NoiseCertification

5.1Noiselimits

6Calculations

6.1Tupolev154MDescription

6.2Noisecalculations

6.2.1Take-offNoiseCalculation

6.2.2LandingApproachNoiseClaculation

7NoiseSuppression

7.1JetNoiseSuppression

7.2DuctLinings

7.2.1DuctLiningCalculation


1 TheNoiseProblem

>Thoughlong ofconcern toneighbors ofmajorairports,aircraftnoisefirstbecame amajor problemwith theintroduction ofturbojet-poweredcommercialaircraft (>Tupolev 104, Boeing 707,DehavillandComet) in thelate1950s.Itwasrecognizedat thetime that thenoiselevelsproducedbyturbojetpoweredaircraftwouldbeunacceptable topersonslivingunder thetake-offpattern ofmajorairports.Accordingly,mucheffortwasdevoted todevelopingjetnoisesuppressors,withsomemodest success.Take-offnoiserestrictionswereimposedbysomeairportmanagements, andnearly allfirst-generationturbojet-poweredtransportswereequippedwithjetnoisesuppressorsat asignificantcost inweight,thrust, andfuelconsumption.

Theintroduction of theturbofanengine,withitslowerjetvelocity,temporarilyalleviated thejetnoise problembutincreased thehigh-frequencyturbomachinerynoise,whichbecame asevere problem onlandingapproachaswellas ontake-off.Thisnoisewasreducedsomewhatbychoosingproperrotor andstatorbladenumbers andspacing andbyusingengines of thesingle-mixed-jettype.

2EffectsOfNoise

>Noiseisoftendefinedasunwanted sound.Togain asatisfactoryunderstanding of theeffects ofnoise, itwouldbeuseful to lookbrieflyat thephysicalproperties of sound.

Soundis theresult ofpressurechanges in amedium,causedbyvibration orturbulence. Theamplitude ofthesepressurechangesisstated interms of soundlevel, and therapiditywithwhichthesechangesoccuris thesound'sfrequency. Soundlevelismeasured indecibels (>dB), and soundfrequencyisstated interms ofcyclesper second orHertz (>Hz). Soundlevel indecibelsis alogarithmicratherthan alinearmeasure of the change inpressurewithrespect to areferencepressurelevel. Asmallincrease indecibelscanrepresent alargeincrease in soundenergy.Technically,anincrease of 3dBrepresents adoubling of soundenergy, andanincrease of 10dBrepresents atenfoldincrease. Theear,however,perceives a10-dBincreaseasdoubling ofloudness.

>Anotherimportantaspectis theduration of the sound, and theway itisdistributed intime.Continuoussoundshavelittle ornovariation intime,varyingsoundshavedifferingmaximumlevelsover aperiod oftime,intermittentsoundsareinterspersedwithquietperiods, andimpulsivesoundsarecharacterizedbyrelatively high soundlevels andveryshortdurations.

Theeffects ofnoisearedeterminedmainlyby theduration andlevel of thenoise,buttheyarealsoinfluencedby thefrequency.Long-lasting,high-levelsoundsare themostdamaging tohearing andgenerally themostannoying.High-frequencysoundstend tobemorehazardous tohearing andmoreannoyingthanlow-frequencysounds. Thewaysoundsaredistributed intimeisalsoimportant, in thatintermittentsoundsappear tobesomewhatlessdamaging tohearingthancontinuoussoundsbecause of theear'sability toregenerateduring theinterveningquietperiods.However,intermittent andimpulsivesoundstend tobemoreannoyingbecause oftheirunpredictability.

>Noisehas asignificantimpact on thequality of life, and in thatsense, itis a health problem. Thedefinition of healthincludestotalphysical andmentalwell-being,aswellas theabsence ofdisease.Noiseisrecognizedas amajorthreat tohumanwell-being.

Theeffects ofnoiseareseldomcatastrophic, andareoftenonlytransitory,butadverseeffectscanbecumulativewithprolonged orrepeatedexposure.Although itoftencausesdiscomfort andsometimespain,noisedoesnotcauseears tobleed andnoise-inducedhearinglossusuallytakesyears todevelop.Noise-inducedhearinglosscanindeedimpair thequality of life,through a reduction in theability tohearimportantsounds and tocommunicatewith family andfriends.Some of theothereffects ofnoise,suchassleepdisruption, themasking ofspeech andtelevision, and theinability toenjoyone'sproperty orleisuretimealsoimpair thequality of life.Inaddition,noisecaninterferewith theteaching andlearningprocess,disrupt theperformance ofcertaintasks, andincrease theincidence ofantisocialbehavior.Thereisalsosomeevidence that itcanadverselyaffectgeneral health andwell-being in thesamemanneraschronicstress.

2.1HearingLoss

>Hearinglossisone of themostobvious andeasilyquantifiedeffects ofexcessiveexposure tonoise.Itsprogression,however,isinsidious, in that itusuallydevelopsslowlyover alongperiod oftime, and theimpairmentcanreach thehandicappingstagebeforeanindividualisaware ofwhathashappened.

>Prolongedexposure tonoise of acertainfrequencypatterncancauseeithertemporaryhearingloss,whichdisappears in afewhours ordays, orpermanentloss. Theformeriscalled >temporarythresholdshift, and thelatterisknownas >permanentthresholdshift.

>Temporarythresholdshiftisgenerallynotdamaging tohumansearunless itisprolonged. People whowork innoisyenvironmentscommonlyarevictims oftemporarythresholdshift.

>Figure 2.1 >Temporarythresholdshiftfor rockbandperformers.

>Repeatednoiseover alongtimeleads topermanentthresholdshift.Thisisespeciallytrue inindustrialapplicationswherepeoplearesubjected tonoises of acertainfrequency.

>Thereissomedisagreementas to thelevel ofnoise thatshouldbeallowedforan8-hourworkingday.Someresearchers and healthagenciesinsist that 85dB(A)shouldbe thelimit.Industrialnoiselevellimitationsareshown in theTable 2.1.

>Table 2.1MaximumPermissibleIndustrialNoiseLevelsByOSHA

(>OccupationalSafety and HealthAct)

SoundLevel,dB(A)

>MaximumDuration

>DuringAny

>WorkingDay

(>hr)

90 8
92 6
95 4
100 2
105 1
110 >
115 >

>Noise-inducedhearinglossisprobably themostwell-defined of theeffects ofnoise.Predictions ofhearinglossfromvariouslevels ofcontinuous andvaryingnoisehavebeenextensivelyresearched andarenolongercontroversial.Somediscussionstillremains on theextent towhichintermittenciesameliorate theadverseeffects onhearing and theexactnature ofdose-responserelationshipsfromimpulsenoise.Itappears thatsomemembers of thepopulationaresomewhatmoresusceptible tonoise-inducedhearinglossthanothers, andthereis agrowingbody ofevidence thatcertaindrugs andchemicalscanenhance theauditory hazardfromnoise.

>Although theincidence ofnoise-inducedhearinglossfromindustrialpopulationsismoreextensivelydocumented,thereisgrowingevidence ofhearinglossfromleisuretimeactivities,especiallyfromsportshooting,butalsofromloud music,noisytoys, andothermanifestations ofour ">civilized"society.Because of theincrease inexposure torecreationalnoise, the hazardfromthesesourcesneeds tobemorethoroughlyevaluated.Finally, therecentevidence thathearingprotectivedevicesdonotperform inactualuse thewaylaboratorytestswouldimply,lendssupport to theneedforreevaluatingcurrentmethods ofassessinghearingprotectorattenuation.

2.2NoiseInterference

>Noisecanmaskimportantsounds anddisruptcommunicationbetweenindividuals in avariety ofsettings.Thisprocesscancauseanythingfrom aslightirritation to aserioussafety hazardinvolvinganaccident oreven afatalitybecause of thefailure tohear thewarningsounds ofimminentdanger.Suchwarningsoundscaninclude theapproach of arapidlymovingmotorvehicle, or the sound ofmalfunctioningmachinery.Forexample,AviationSafetystates thathundreds ofaccidentreportshavemany ">sayagain"exchangesbetweenpilots andcontrollers,althoughneithersidereportsanythingwrongwith theradios.

>Noisecandisrupt face-to-face andtelephoneconversation, and theenjoyment of radio andtelevision in thehome.Itcanalsodisrupteffectivecommunicationbetweenteachers andpupils inschools, andcancausefatigue andvocalstrain inthose whoneed tocommunicate inspite of thenoise.Interferencewithcommunicationhasproved tobeone of themostimportantcomponents ofnoise-relatedannoyance.

>Interferencewithspeechcommunication andothersoundsisone of themostsalientcomponents ofnoise-inducedannoyance. Theresultingdisruptioncanconstituteanythingfromanannoyance to aserioussafety hazard,depending on thecircumstance.

>Criteriafordeterminingacceptablebackgroundlevels inroomshavealsobeenexpanded andrefined, andprogresshasbeenmade on thedevelopment ofeffectiveacousticwarningsignals.

>Itisnowdear thathearingprotectiondevicescaninterferewith theperception ofspeech andwarningsignals,especiallywhen thelistenerishearingimpaired,bothtalker andlistenerwear thedevices, andwhenwearersattempt tolocate asignal'ssource.

>Noisecaninterferewith theeducationalprocess, and theresulthasbeendubbed ">jet-pauseteaching"aroundsome of thenation'snoisierairports,butrailroad andtrafficnoisecanalsoproducescholasticdecrements.

2.3 SleepDisturbance

>Noiseisone of themost commonforms ofsleepdisturbance, andsleepdisturbanceis acriticalcomponent ofnoise-relatedannoyance. Astudyusedby EPA inpreparing theLevelsDocumentshowed thatsleepinterferencewas themostfrequentlycitedactivitydisruptedbysurfacevehiclenoise (>BBN, 1971).Aircraftnonecanalsocausesleepdisruption,especially inrecentyearswith theescalation ofnighttimeoperationsby theaircargoindustry.Whensleepdisruptionbecomeschronic,itsadverseeffects on health andwell-beingarewell-known.

>Noisecancause thesleeper toawakenrepeatedly and toreportpoorsleepquality the nextday,butnoisecanalsoproducereactions ofwhich theindividualisunaware.Thesereactionsincludechangesfromheavier tolighterstages ofsleep,reductions in ">rapideyemovement"sleep,increases inbodymovementsduring thenight,changes incardiovascularresponses, andmoodchanges andperformancedecrements the nextday,with thepossibility ofmoreseriouseffects on health andwell-beingif itcontinuesoverlongperiods.

2.4NoiseInfluence on Health

>Noisehasbeenimplicated in thedevelopment orexacerbation of avariety of healthproblems,rangingfromhypertension topsychosis.Some ofthesefindingsarebased oncarefullycontrolledlaboratory orfield research,butmanyothersare theproducts ofstudies thathavebeenseverelycriticizedby the research community.Ineithercase,obtainingvaliddatacanbeverydifficultbecause of themyriad ofinterveningvariables thatmustbecontrolled,suchasage,selectionbias,preexisting healthconditions,diet,smokinghabits,alcoholconsumption,socioeconomic status,exposure tootheragents, andenvironmental andsocialstressors.Additionaldifficultieslie in theinterpretation of thefindings,especiallythoseinvolvingacuteeffects.

>Loudsoundscancauseanarousalresponse inwhich aseries ofreactionsoccur in thebody.Adrenalinisreleasedinto thebloodstream;heartrate,bloodpressure, andrespirationtend toincrease;gastrointestinalmotilityisinhibited;peripheralbloodvesselsconstrict; andmusclestense.Eventhoughnoisemayhavenorelationship todanger, thebodywillrespondautomatically tonoiseas awarningsignal.

3NoiseSources

>Allnoiseemanatesfromunsteadiness timedependence in theflow.Inaircraftenginestherearethreemainsources ofunsteadiness:motion of thebladingrelative to theobserver,whichifsupersoniccangiverise topropagation of asequence ofweakshocks,leading to the >buzzsawnoise ofhigh-bypassturbofans;motion ofoneset ofbladesrelative toanother,leading to apure-tome sound (>like thatfromsiren)whichwasdominant onapproach inearlyturbojets; andturbulence orotherfluidinstabilities,whichcanlead toradiation of soundeitherthroughinteractionwith theturbomachineblading orothersurfaces orfrom thefluidfluctuationsthemselves,as injetnoise.

3.1JetNoise

Whenfluidissuesas ajetinto astagnant ormoreslowlymovingbackgroundfluid, theshearbetween themoving andstationaryfluidsresults in afluid-mechanicalinstability thatcauses theinterface tobreak upintovorticalstructuresasindicated inFig. 3.1. Thevorticestraveldownstreamat avelocitywhichisbetweenthose of the high andlowspeedflows, and thecharacteristics of thenoisegeneratedby thejetdepend onwhetherthispropagationvelocityissubsonic orsupersonicwithrespect to theexternalflow.Weconsiderfirst thecasewhere itissubsonic,asiscertainly thecaseforsubsonicjets.

>Figure 3.1 Asubsonicjetmixingwithambientair,showing themixinglayer

>followedby thefullydevelopedjet.

For thesubsonicjets theturbulence in thejetcanbeviewedas adistribution ofquadrupoles.

3.2TurbomachineryNoise

Turbomachinerygeneratesnoisebyproducingtime-dependentpressurefluctuations,whichcanbethought of infirstapproximationasdipolessincetheyresultfromfluctuations inforce on theblades orfrompassage ofliftingbladespast theobserver.

Itwouldappearatfirst thatcompressors orfansshouldnotradiate sounddue toblademotionunless thebladetipspeedissupersonic,butevenlow-speedturbomachinesdo infactproduce agreat deal ofnoiseat thebladepassingfrequencies.

4NoiseMeasurement andRules

Humanresponsesets thelimits onaircraftenginenoise.Although thelogarithmicrelationshiprepresentedby thescale ofdecibelsis afirstapproximation tohumanperception ofnoiselevels, itisnotnearlyquantitativeenoughforeithersystemsoptimization orregulation.Muchefforthasgoneinto thedevelopment ofquantitativeindices ofnoise.

4.1NoiseEffectiveness Forecast (>NEF)

Itisnot thenoiseoutput ofanaircraftperse thatraisesobjectionsfrom theneighborhood of amajorairport,but thetotalnoiseimpact of theairportsoperations,whichdepends ontake-offpatterns,frequencies ofoperationatdifferenttimes of theday,populationdensities, and ahost oflessobviousthings.Therehavebeenproposals tolimit thetotalnoiseimpact ofairports, and ineffectlegalactionshavedonesofor themostheavilyusedones.

Onewidelyacceptedmeasure ofnoiseimpactis theNoiseEffectiveness Forecast (>NEF),whichisarrivedatasfollowsforanylocationnearanairport:

1.Foreachevent,compute theEffectivePerceivedNoiseLevel (>EPNL)by themethods of ICAOAnnex 16,asdescribedbelow.

2.Foreventsoccurringbetween 10PM and 7AM,add 10 to theEPNdB.

3.ThenNEF = ,where thesumis takenover allevents in a24-hourperiod. Alittlecipheringwillshow thatthis lastcalculationisequivalent toadding theproducts of soundintensitytimestimefor allevents,thentaking thedBequivalent ofthis. Thesubtractor 82isarbitrary.

4.2EffectivePerceivedNoiseLevel (>EPNL)

Theperceivednoisiness ofanaircraftflyoverdepends on thefrequencycontent,relative to theearsresponse, and on theduration. Theperceivednoisinessismeasured inNOYs (>unit ofperceivednoisiness) andisplottedas afunction of soundpressurelevel andfrequencyforrandomnoise inFig. 4.1.


>Figure 4.1Perceivednoisinessas afunction offrequency and soundpressurelevel

>Puretones (>frequencieswithpressurelevelsmuchhigherthan that of theneighboringrandomnoise in the soundspectrum)arejudged tobemoreannoyingthananequal soundpressure inrandomnoise,so a >tonecorrectionisadded totheirperceivednoiselevel. A >durationcorrectionrepresents theidea that thetotalnoiseimpactdepends on theintegral of soundintensityovertimefor agivenevent.

The 24one-thirdoctavebands of soundpressurelevel (>SPL)areconverted toperceivednoisinessbymeans of anoytable.

>Figure 4.2 >Perceivednoiselevelas afunction ofNOYs

>Conceptually, thecalculation ofEPNLinvolves thefollowingsteps.

1.Determine theNOYlevelforeachband andsumthemby therelation

,

>where >kdenotesaninterval intime, denotes theseveralfrequencybande, and >n(k)is theNOYlevel of thenoisiestband.Thisreflects the >masking oflesserbandsby thenoisiest.

2. ThetotalPNListhenPNL(>k) = 40 + 33.3log10>N(k).

3.Apply atonecorrection >c(k)byidentifying thepuretones andadding toPNLanamountrangingfrom 0 to 6.6dB,depending on thefrequency of thetone anditsamplituderelative toneighboringbands.

4.Apply adurationcorrectionaccording toEPNL =PNLTM + D,wherePNLTMis themaximumPNLforany of thetimeintervals.Here

,

>where D>t = 0.5sec, T = 10sec, and >dis thetimeoverwhichPNLTexceedsPNLTM 10dB.Thisamounts tointegrating the soundpressurelevelover thetimeduringwhich itexceedsitspeakvalueminus 10dB,thenconverting theresult todecibels.

>Allturbofan-poweredtransportaircraftmustcomplyatcertificationwithEPNLlimitsformeasuringpointswhicharespokenabout in the nextchapter.

5NoiseCertification

Theincreasingvolume ofairtrafficresulted inunacceptablenoiseexposuresnearmajorurbanairfields in thelate1960s,leading to agreat publicpressurefornoise control.Thispressure, andadvancingtechnology,led to ICAOAnnex 16,AP-36,JointAviationRegulationPart 36 (>JAR-36) andFederalAviationRulePart 36 (>FAR-36),whichsetmaximumtake-off,landing and >sidelinenoiselevelsforcertification of newturbofan-poweredaircraft.Itisthrough theneed tosatisfythisrule that thenoiseissueinfluences thedesign andoperation ofaircraftengines. Alittlemoregeneralbackground of thenoise problemmaybehelpful inestablishing thecontext ofenginenoise control.

The FAAissuedFAR-36 (>whichestablishes thelimits ontake-off,approach, andsidelinenoiseforindividualaircraft),followedby ICAOissuingitsAnnex 16Part 2, andJAAissuingJAR-36.Theseruleshavesincebeenrevisedseveraltimes,reflectingbothimprovements intechnology andcontinuingpressure toreducenoise.As ofthiswriting, therulesareenunciatedasthreeprogressivestages ofnoisecertification. Thenoiselimitsarestated interms ofmeasurementsatthreemeasuringstations,asshown inFig. 5.1:under theapproachpath 2000mbeforetouchdown,under thetake-offpath 6500mfrom thestart of thetake-offroll, andat thepoint ofmaximumnoisealong thesides of therunwayat adistance of 450m.

>Figure 5.1 >Schematic ofairportrunwayshowingapproach,take-off, and

>sidelinenoisemeasurementstations.

Thenoise ofanygivenaircraftat theapproach andtake-offstationsdependsboth on theengines and on theaircraftsperformance,operationalprocedures, andloading,since the powersettings and thealtitude of theaircraftmayvary.

Thesidelinestationismorerepresentative of theintrinsictake-offnoisecharacteristics of theengine,since theengineisatfullthrottle and thestationisnearlyat afixeddistancefrom theaircraft. Theactualdistancedepends on thealtitude theaircrafthasattainedwhen itproducedmaximumnoisealong thedesignatedmeasuring line.SinceFAR-36 andinternationalrulessetby the InternationalCivilAviationOrganization (ICAOannex 16,Part 2)whicharegenerallyconsistentwith ithavebeen inforce,airportnoisehasbeen amajordesigncriterionforcivilaircraft.

>Stricternoisepollutionstandardsforcommercialaircraft,establishedby the InternationalCivilAviationOrganization,cameintoeffectworldwide on 1April.Mostindustrializedcountries,including all EUstates,enforced the newrules and thevastmajority ofairlinersflying inthosestatesalreadymeet themorestringentrequirements.ButsomeEastern Europeancountriesarefacing a problem,especially Russia.Eightypercent ofitscivilianaircraftfallshort of thestandards,meaning itwillnotbeable toapply the newrulesfor domesticflights.Evenmoreworrisomefor Moscowis thefact that Russiacouldfindmany ofitsplanesbannedfromforeignskies.Enforcement of the newrulescouldforce Russia tocancel 11,000flights in 2002,representingsome 12percent of thecountry'spassengertraffic.

The newruleshavebeenappliedonly tosubsonictransports,becauseno newsupersoniccommercialaircrafthavebeendevelopedsinceitspromulgation.

5.1NoiseLimits

>Asmentionedabove, allturbofan-poweredtransportaircraftmustcomplyatcertificationwithEPNLlimitsfor thethreemeasuringstationsasshown inFig. 5.1. Thelimitsdepend on thegrossweight of theaircraftattake-off andnumber ofengines,asshown inFig. 5.2. Theruleis thesamefor allenginenumbers onapproach and on thesidelinebecause thedistancefrom theaircraft to themeasuringpointisfixed onapproachby theangle of theapproachpath (>normally 3deg) and on thesidelineby thedistance of themeasuringstationfrom therunwaycenterline.

>Figure 5.2 >Noiselimitsimposedby ICAOAnnex 16forcertification ofaircraft.

>Ontake-off,however,aircraftwithfewerenginesclimb outfaster,sotheyarehigherabove themeasuringpoint.Here the >reasonable andeconomicallypracticableprinciplecomesintodictate thatthree-engine andtwo-engineaircrafthavelowernoiselevelsat thetake-offnoisestationthanfour-engineaircraft.

Thereissomeflexibility in therule, in that thenoiselevelscanbeexceededby up to 2EPNdBatanystationprovided thesum of theexceedancesisnotover 3ENPdB and that theexceedancesarecompletelyoffsetbyreductionsatothermeasuringstations.


6NoiseLevelCalculations

6.1Tupolev154MDescription

>Formostairlines in the CIS, theTupolevTu-154isnowadays theworkhorse on domestic andinternationalroutes.

>Figure 6.1 >Tupolev154Mmain look

>Itwasproduced in twomainvesions: TheearlierproductionmodelshavebeendesignatedTupolev -154,Tupolev ->154A,Tupolev ->154B,Tupolev ->154B-1 andTupolev ->154B-2,while thelaterversionhasbeencalledTupolev ->154M.Overall,close to 1'000Tupolev ->154swerebuilt up today, ofwhich alargeportionisstilloperated.


>Table 6.1 >Tupolev154Mmaincharacteristics

 

>Role

>Mediumrangepassengeraircraft

Status

>Produceduntilcirca 1996, inwidespread service

>NATOCodename

>Careless

First Flight

>October 3, 1968

First Service

1984

>Engines

3SolovievD-30KU (104kNeach)

>Length

47.9m

>Wingspan

37.5m

>Range

3'900km

>CruisingSpeed

900km/h

>PayloadCapacity

156-180passengers (5450kg)

>MaximumTake-offWeight

100'000kg

TheTu-154wasdeveloped toreplace theturbojetpoweredTupolevTu-104,plus theAntonov - 10 andIlyushin - 18turboprops. Designcriteria inreplacingthesethreerelativelydiverseaircraftincluded theability tooperatefromgravel orpacked earthairfields, theneed toflyat highaltitudes '>abovemostSoviet Unionairtraffic, andgoodfieldperformance.Inmeetingtheseaims theinitialTupolev -154designfeaturedthreeKuznetsov (>nowKKBM)NK-8turbofans,triplebogeymainundercarriageunitswhichretractintowingpods and arearengineT-tailconfiguration.

TheTupolev ->154'sfirstflightoccurred onOctober 4 1968.Regularcommercial servicebegan inFebruary 1972. ThreeKuznetsovpoweredvariants of theTupolev -154werebuilt, theinitialTupolev -154, theimprovedTupolev ->154Awithmorepowerfulengines and ahighermaxtake-offweight and theTupolev ->154Bwith afurtherincreasedmaxtake-offweight.Tupolev ->154Sis afreighterversion of theTupolev ->154B.

>Currentproductionis of theTupolev ->154M,whichfirstflew in 1982. Themajor changeintroduced on the Mwas thefarmoreeconomical,quieter andreliableSolovyev (>nowAviadvigatel)turbofans. TheTupolev -154M2is aproposedtwinvariantpoweredby twoPermPS90Aturbofans.

6.2NoiseCalculaions

>Noiselevelat controlpointsiscalculatedusing theNoise-Power-Distance (NPD)relationship.InpracticeNPD-relationshipisused in theparabolicshape:

,

>wherecoefficients , , aredifferentfordifferentaircrafttypes andenginemodes.ForTupolev-154M thecoefficients , , areshown in thetable 6.2 inrespect toTupolev-154.

>Table 6.2Noise-Power-Distancecoefficients ofsimilaraircraft.

>Tupolev-154 >Tupolev-154M
>Enginemode A B A B
>Maximal 145.45 -15.66 -0.81 142.53 -15.52 -0.83
>Nominal 142.14 -15.56 -0.82 137.58 -14.28 -1.09
85% ofnominal 140.50 -16.29 -0.76 142.84 -17.75 -0.78
>Cruise 140.23 -16.35 -1.15 137.56 -16.07 -1.10
>2-ndcruise 131.03 -10.38 -2.23 130.07 -11.54 -2.00
>Descending 126.84 -11.86 -1.93 128.57 -14.25 -1.39
>Idle 132.37 -16.36 -0.86 134.92 -17.13 -0.68

6.2.1Take-offNoiseCalculation

Theaircraftbegins thetake-offrollatpoint A (>Fig. 6.2),lifts offatpoint B, andinitiates thefirstconstantclimbatpoint atanangle. Thenoiseabatementthrustcutbackisstartedatpoint D andcompletedatpoint Ewhere the secondconstantclimbisdefinedby theangle (>usuallyexpressed interms of thegradient inpercent). The end of thenoisecertificationtake-offflightpathisrepresentedbyaircraftposition Fwhoseverticalprojection on theflight track (>extendedcenterline of therunway)ispoint M. Theposition of theaircraftmustberecordedfor theentireintervalduringwhich themeasuredaircraftnoiseleveliswithin 10dB ofPNLTM. Position Kis thetake-offnoisemeasuringstationwhosedistanceAKisspecifiedas 6500meters.

>Figure 6.2 >Take-off andclimbpath

 

Thetake-offprofileisdefinedbyfiveparameters -- (A)AB, thelength oftake-offroll; (B) thefirstconstantclimbangle; (), the secondconstantclimbangle; and (D), and e, thethrustcutbackangles.Thesefiveparametersarefunctions of theaircraftperformance andweight, and theatmosphericconditions oftemperature,pressure, andwindvelocity anddirection.

>Underreferenceatmosphericconditions andwithmaximumtake-offweight, thegradient of the secondconstantclimbangle (>)maynotbelessthan 4percent.However, theactualgradientwilldependuponatmosphericconditions,assumingmaximumtake-offweight and theparameterscharacterizingengineperformanceareconstant (>rpm, oranyotherparameterusedby thepilot).

>Inoperationalconditions theclimbisperformedwithout thecutbackstage, and theaircraftfliesover the controlpointat aloweraltitude,whichleads tohighernoiselevels.

>Figure 6.3Comparisonbetweenoperational andcertificationtrajectories

 

TheclimbpathforTupolev154Mwascalculatedusing thefollowingequation

>where:

>misaircraft mass;

>Pisthrust;

ais theangle ofattack, jis theangle ofengineinstallation;

>qisclimbanglewhichisequal to b or g,depending on theclimbstage.

>Figure 6.4Comparisonbetweennoiselevelsunderdifferentflightpaths

6.2.2ApproachNoiseCalculation

Theapproachesmustbeconductedwith asteadyglideangle of 30.5 andmustbecontinued to anormaltouchdownwithnoairframeconfiguration change.Thus thedistancefrom the controlpoint to theglideslope RN >remainsconstant andisequal to 119.7m.


>Figure 6.5Schematic ofapproach

Takingintoaccount that thespeedremainsconstant andairframeconfigurationisforlanding,wecancalculate thestallspeed:

,

>where Gisairplaneweight, >risairdensity, P.S >iswingarea, ymaxismaximumliftcoefficientdeterminedfromFig. 6.6.

>Approachspeedshouldbe 30%greater that thestallspeed:

>Figure 6.6Aerodynamiccharacteristics ofTupolev154M.

>Using theapproachspeed,wecancalculatecurrentliftcoefficient:

.

>CorrespondingdragcoefficientisdeterminedfromFig. 6.6.

>Somecorrectionsmustbemade tocalculatedvalues ofdrag andliftcoefficients.Itisnecessary totakeintoaccount theinfluence of thelandinggearwhichcreatesadditionaldrag anddecreaseslift. Theinfluence offlaps andslatsislittle andcanbeneglected.

>Necessarythrustiscalculatedusing thefollowingformula

,

>where >isdrag and >qisapproachpathanglewhichisequal to 3degrees.

>Calculatedresultsforfivedifferentlandingweightsareshown in thetable 6.3.

>Table 6.3 >CalculationresultsforTupolev154Matapproachconfiguration.

 

>Weight, %MLW >MLW 95% 90% 85% 80%
>Weight,kg 80000 76000 72000 68000 68000
>Vapp,m/s 74,8 72,91 70,964 68,965 66,91
>Thrust,kg 8445,63 8024,67 7601,88 7179,66 6758,58

LA,dBA

96,74 96,05 95,35 94,66 93,97
>EPNL,EPNdB 112,17 111,32 110,48 109,64 108,79
>LA,dBA 0 0,69 0,7 0,69 0,69
>EPNL,EPNdB 0 0,85 0,84 0,84 0,85
>SQRT (>WingLoad) 21,082 20,548 20 19,437 18,856
>ThrustToWeightrt. 0,10557 0,105588 0,105582 0,105583 0,105603

 

>Tupolev154Mhas thesameaerodynamicsasTupolev 154,thus thenecessarythrustforboth ofthemduringapproachisalmost thesame.Tupolev154Mhasmorepowerfulengines and itcancarrymorepayload.Itsmaximumlandingweightis 2tonsgreaterthan thatone of 154.Noiseparametersaredifferentfortheseaircraft (>table 6.2), and thecalculatednoiselevelsslightlydifferaswell.


7NoiseSuppression

7.1Suppression ofJetNoise

>Methodsforsuppressingjetnoisehaveexploited thecharacteristics of thejetitself andthose of thehumanobserver.For agiventotalnoise power, thehumanimpactislessif thefrequencyisvery high,as theearislesssensitiveat highfrequencies. Ashift to highfrequencycanbeachievedbyreplacingonelargenozzlewithmanysmallones.Thiswasonebasisfor theearlyturbojetenginesuppressors.Reduction of thejetvelocitycanhave apowerfuleffectsince >P >isproportional to thejetvelocityraised to a powervaryingfrom 8 to 3,depending on themagnitude of u. Themultiplesmallnozzlesreduced themeanjetvelocitysomewhatbypromotingentrainment of thesurroundingairinto thejet.Someattemptshavebeenmade toaugmentthiseffectbyenclosing themultinozzle in ashroud,so that theambientairisdrawninto theshroud.

>Certainly themosteffective ofjetnoisesuppressorshasbeen theturbofanengine,which ineffectdistributes the power of theexhaustjetover alargerairflow,thusreducing themeanjetvelocity.

>Injudging theoverallusefulness ofanyjetnoise reductionsystem,severalfactorsmustbeconsidered inaddition to theamount ofnoise reduction.Amongthesefactorsareloss ofthrust,addition ofweight, andincreasedfuelconsumption.

Anumber ofnoise-suppressionschemeshavebeenstudied,mainlyforturbofanengines ofonesort oranother.Theseincludeinverted-temperature-profilenozzles, inwhich ahotouterflowsurrounds acoolercoreflow, andmixer-ejectornozzles.In thefirst ofthese, theeffectis toreduce theoverallnoiselevelfrom thatwhichwouldbegeneratedif thehotouterjetsaresubsonicwithrespect to theouterhotgas.Thisideacanbeimplementedeitherwith aductburner on aconventionalturbofan orwith anozzle thatinterchanges thecore andductflows,carrying thelatter to theinside and theformer to theoutside.In themixer-ejectornozzle, theideais toreduce themeanjetvelocitybyingestingadditionalairflowthrough acombination of theejectornozzles and thechute-typemixer.Fairly high massflowratioscanbeattainedwithsucharrangements,at theexpense ofconsiderableweight.

Themostpromisingsolution,however,issomeform of >variablecycleengine thatoperateswith ahigherbypass ratio ontake-off and insubsonicflightthanat thesupersoniccruisecondition.Thiscanbeachieved tosomedegreewithmulti-spoolenginesbyvarying thespeed ofsome of thespools to changetheir massflow, andat thesametimemanipulatingthrottleareas.Anotherapproachis touse atandem-parallelcompressorarrangement,where twocompressorsoperate inparallelattake-off andsubsonically, and inseriesat asupersonicconditions.

7.1.1DuctLinings

>Itisselfevident that themostdesirableway toreduceenginenoisewouldbe toeliminatenoisegenerationbychanging theenginedesign. Thecurrent state of the art,however,willnotprovidelevelslowenough tosatisfyexpectedrequirements;thus, itisnecessary toattenuate thenoise thatisgenerated.

>Fannoiseradiatedfrom theengineinlet andfandischarge (>Fig. 7.1) ofcurrentfanjetairplanesduringlandingmakes thelargestcontribution toperceivednoise.

>Figure 7.1 >Schematicillustration ofnoisesourcesfromturbofanengines

>Figure 7.2.shows atypicalfarfieldSPLnoisespectrumgeneratedby aturbofanengineat alanding-approach powersetting.Below 800Hz, thespectrumiscontrolledbynoisefrom theprimaryjetexhaust. Thespectrumbetween 800 and 10000Hzcontainsseveraldiscretefrequencycomponents inparticular thatneed tobeattenuatedby thelinings in theinlet and thefanductbeforetheyareradiated to thefarfield.

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