DOC

Hydrodynamic characteristics of the surface-piercing propellers for the planing craft

By Ellen Elliott,2014-01-21 19:22
8 views 0
Hydrodynamic characteristics of the surface-piercing propellers for the planing craft

    Hydrodynamic characteristics of the surface-piercing propellers for the planing

    craft

    J.Marine.Sci.App1.(2009)8:267274

    DOI:10.1007/s11804.009.80762

    Hydrodynamiccharacteristicsofthesurface--piercing

    propellersfortheplaningcraft

    HassanGHASSEMI

    DepartmentofMarineTechnology,AmirkabirUniversityofTechnology,Tehran15875

    4413,Iran

    Abstract:Demandforhigh

    speedmarinevehicles(HSMVs1ishighamongbothcommercialandnaval

    users.Itisthedutyofthemarinevessel'sdesignertoprovideahul1andpropulsionsystemthat diminishesdrag,improvespropulsiveefficiency,increasessafetyandimprovesmaneuverability.From

    thepropulsorside,surfacepiercingpropellers(SPPs)shouldimproveperformance.Unlikeimmersed

    propellers.behavioroftheSPPisaffectedbydepthofimmersion.Webernumberandshaftinclination

    angle.Thispaperusesapracticalnumerica1methodtopredictthehydrodynamiccharacteristicsofan

    SPP.ThecriticaladvancevelocityratioisderivedusingtheWebernumberandpitchratiointhe transitionmode,thenthepotentialbasedboundaryelementmethod(BEM)isusedontheengaged

    surfaces.TwomodelsofthreeandsixbladedSPPs(SPP1andSPP

    2,wereselectedandsomeresults

areshown.

    Keywords:surfacepiercingpropeller;boundary CLCnumber:U664-33Documentcode:A

    1Introduction

    elementmethod;hydrodynamiccharacteristics ArticleID:1671--9433(2009)04--0267--08

    ItiSthenava1architectstasktodesignthemarinevehicles inordertoreachthesix.Spossessions(stable,shipment, strength,safety,stealthandspeed),whichareinteresting forallownersofmerchantandnavalvessels.tono allthepossiblewayshavebeenconsideredforincreasing thespeedofvessels.Surfacepropellersmountedcloseto thetransomandonshaftsextendedaftofthetransomhave provedtheireffectivenessonoperationalcraft.For steering,somesurfacepropellersaremountedon articulatedshaflsandothershaverudderswhichareoften locatedaftofthepropeller.Apairofsurfacepropellers maybethehighestpowerunitdemonstratedonan operationalcrafttodate.

    AnSPPisaspecialtypeofsuper-cavitatingpropeller, whichoperatesatpartiallysubmergedconditions.SPPs aremoreefficientthanimmersedpropellersbecauseof somereasonssuchas:

    ?Decreasedpowerbyreducingtheappendagesdrag likeshafts,struts,propellerhub;

    ?Largerpropellerdiametersinceitssizeisnotlimited bythebladetipclearancefromthehullorthe

    maximumvesseldraft;

    nReductionofthebladesurfacefrictionanderosion, sincecavitationisreplacedbyventilation;

    ?Generatingthevertica1forcetoobtaintheoptimum runningtrim.

    Receiveddate:200811.03.

    CorrespondingauthorEmail:gasemi@autac.ir ?Decreasingthetorqueandgivingthehigher efficiency.

    SPPsworkintheairandwaterduringarotation.It operatesabouthalfofthetimeintheair,onethirdofthe

    timeiscompletelysubmergedandtherestispartly submerged(intheentryandexitphases).WhentheSPPis workingatpartiallysubmergedphase,onlytheface (pressureside)iswetted,whilethebacksideissurrounded byanairconnectedtothefreesurface.Onthebackside, thepressureisapparentlyequaltotheatmospheric pressure,whilealargepressureactsontheface.Because ofthat,somepeculiarphenomenahavetobetakeninto accountandnumericalmodelingiscomplicatedinthis systembydifferentpropertiesappliedtothem. ForSPPsystems.efficientexperimenta1andnumerical approachesarescarce.Thereareanumberofpublications onthemodelseriesincavitationtunnelsinvarious conditions.RuseandKruppaandKruppa.etalcarried

    outmodeltestsoftheSPPatvariouspitchratios. Experimenta1workonthepropulsiveperformanceofthe SPPwithwedgesectionwascompletedbyNozawa& Takayamat.

    Recently,Pustoshny,etal..presentedthe

    resultsofvariOUSgeometricalandoperationalparameters onthehydrodynamiccharacteristicsofthe5.bladeSPP seriesforthefastboats.Inthepastdecade,Ferrandoet

    a1Jhaveecientlycarriedoutexperimenta1testsand obtainedectofparameterssuchasimmersiondepth. axia1shaftslope.Webernumber,pitchratioonthe hydrodynamiccharacteristicsoftheSPPs.Also,some experimentalworkofthesurfacepiercingpropellerswas 268HassanGHASSEMZHydro4vnami~charactert~n'csofthesH

    ce-piercingpropellers"fortheplaningcraft alSope:rformedbyOlofsson[.

    Young&Kinnas[

    presentedanumerica1approachusingBEMforthe analysisofsuper-cavitatingandsurfacepiercingpropeller flows.Recently,Ghassemi&Ghiasit"andGhassemi& Shademani[13JdevelopednumericalcalculationsoftheSPP fortheplaningcraftsusingacombinednumerica1and practicalapproach.

    Inthisstudy,aspeciallypracticalandnumericalmethod hasbeenusedtopredictthehydrodynamiccharacteristics oftheSPP.UsingWebernumberandpitchratio.Ferrando eta1.obtainedcriticaladvancevelocityratiobypractica1 formulainansitionmode.InthisPaper,anumerical methodisemployedusingpotentia1basedboundary elementmethod(BEM)ontheengagedsurfaces.Two modelsofthreeandsixbladedSPPsareselectedand

    someresultsareshown.Thefirstpropeller'sresultswere comparedwithexperimentalresultsandhydrodynamic operati0n0fSPP.2waspresentedatvariouspitchratios. 2SPPsystemforHigh-SpeedVessels

    uptonow,manypropulsortypessuchasconventional singlepropeller,twinpropeller,ductedpropeller,CRP,

    AZIPOD,super-cavitatingpropeller,water-jetandSPP

    havebeeninstalledforthemarinevehicles,ascategorized inFig.1.

    NowadaysSPPsarepopularforthehighspeedcraftsfor

    somereasons.Whenthespeedisincreased,theinduced hydrodynamicpressuregeneratesonthebottomofthehull anditmakesthecraftraised.Then,theresistanceofthe craftisdiminishedwheninfullyplaningmode.Ifmehull ofthecraftjswel1.designedandtheenginehastheability todeliverthepowertothepropulsionsystemwith receivingmaximumeciencytoo.itispossibleforthe

    vesse1topassthehumpmode.Inthecaseofthe

    submergedpropeller,theshaftofthepropellershouldbe inclinedmore,sothatthepropellerperformance diminishes.ItismoreadvantageoustousetheSPPsto reachbetterperformance.Thebehaviorofthe hydrodynamicresistanceagainstvolumetricFroude numberoftheplaningcrafthasthreemodes.Atlower speed(v<1.2),theplaningcraftresortstobuoyancy forsupport(displacementmode),whereasatforward speeds(1.2<v<2.5),acombinationofhydrostatic andhydrodynamicsupportingforcesexists(semi- displacementmode).Atv>2.5,generated

    hydrodynamicsupportingforcesonanimmersedhull causetheraiseofthehullinwater,decreasethewetted surfaceandsubsequentlydiminishtheresistance.When thecraftsspeedisincreased.thewel1.designedhullraises upduetogenerationofthehydrodynamicpressureatthe bottom.Intheseconditions,shaftandpropellerthrust systernshouldbesetuDataleve1.whichcanprovidethe bestperformance.SPPshavebeenusedsuccessfullyfor

misapplication.

    Fig.1Propulsortypesforthemarinevehicles 3MaineffectiveparametersinSPP

    design

    Foraconventionalpropellerthrustandtorque, coefficientsdependonthediameter,pitch,numberof blades,expandedarearatio,advancevelocityratio, Froudenumber,Reynoldnumber,cavitationnumberand shaftinclinationangle.

    l1v.mm.ed=f(Z,/D,EAR,J,F,Rn,,)(1)

    Aspartiallysubmergedpropellersoperateatthe interfacebetweenairandwater,twoadditiona1 parametersmustbetakenintoaccount.Thefirstoneis JournalofMarineScienceandApplicationf2009,8:267274

    theimmersioncoefficientI'thesecondistheWeber

    number,whichcanbeformulatedas

    =

    f(Z,P/D,EAR,J,F,,cr,T,',)(2)

    whereWebernumberandimmersedratioaredefinedas ,:?

    andisthekinematics'capillarity

    f3

    Theinfluenceofthenumberofblades.pitchratio. expandedarearatioandadvancevelocityratioonthe behaviorofaSPPisthesameasincaseofafully immersedpropeller.ThesameistruefortheReynolds Number.Efiectivenessofbladesectionisalsovery important.ThebladesectionshouldbeselectedforSPP togeneratehigher1ifltodragratio.SomeSPPsections areshowninFig.2.

    Moreover,theinstallationofSPPsisverysensitivefor hydrodynamicsperformance;hence,shaftangleand immersedratiocandeterminethepropellerperformance. Fig.2VarioussectionsofSPPs

    Ferrando,etal[]distinguishedandexperimentally obtainedthecriticaladvancevelocityratiobyusing regressionmethod,asexpressedby

    JcR:Kl+2e)

    

    (4)

    Thispracticalformuladependsontwofactors.i.e.pitch ratioandWebernumber.Thevaluesofregression coefficients(1,,.(11aredifferentanddependonthe propellertypes.Bytrialanderrorandinvestigationof otherstudies,thesecoefficientsmaybeobtainedfor SPP1andSPP.2.Fig.3showstheestimatedcritical advancevelocityratioagainstWebernumber.Itisclear thatwhenthe,Vebernumberisgreaterthan250 (W,>250),theadvancevelocityratiobecomesconstant andthepropelleroperatesatthefullyventilatedzone.It

    meansthatthebacksideofthebladeisoccupiedbythe airwithatmosphericpressure.Therefore,thefacesideof 269

    thebladeiswetthatisactedbyhighpressure,inwhich thethrustortorqueisgenerated.

    ff|,J

    Fig.3PredatedinfluenceofWebernumber()andpitch ratioP/DoncriticaladvancevelocityratioJ cR

    4Numericalformulas

4.1Propellergeometric

    Coordinationofshaftandpropellersystemisshownin Fig.4.Thesupposedimpellerrotatescounterclockwise withfixedangularspeedininviscid.irrotationaland incompressibleflow.CartesianCO0rdinatessystem (O-xyz)withoriginOfixedinpropellercenter. Consideringthexaxisiscoincidingtopropelleraxisand positivedirectionsofxandz.axisaredownwardand upwardrespectively,andthey-axiscompletesright-hand COOrdinatesystem,apointcoordinateonKthblade surfaceisexpressedasfollows:

    xB

    ,F=rtan+((r)+L(r))sinfl~,COS

    Y":rcos(r/+8k,

    zBF=rsin(r/8F+Ok,

    Andthat

    ,

    ,=

    l((r)+L(r))cosflr+,sinfirI/r

    =

    2n(k1)/Zk=1,2,,z

    D

    =arctan(?)

    y:Rakeangle.

    r):Distancefromgeneratinglinetoleadingedge. (r):Distancefromleadingedgetotrailingedge. YBP:Forwardandbackwardcoordinatefrombaseline Z:Bladenumberofthepropeller.

    OK:Bladeindexangle.

    r:Radia1coordinateofthepropeller.

Pr:Geometrypitchangle.

    Po:Geometrypitchofpropeller.

    (5)

    (6)

    Shaftinclinationisalsoimportantincaseofshaft inclination,advancedvelocityratio.isdefinedas J=COS

    nD

    (7)

    270HassanGHASSEMI.HydrodynamiccharacteristicsoftheSU

    ce-piercingpropellersfo,theplaningcraft Fig.4Shaftandpropellercoordinatesystem 4.2Boundaryelementmethodandgoverning

    equation

    AboundaryintegralmethodinvolvingGreen'Sfunction isusedtosolvetheboundaryvalueproblem.Green'S identitycanbeappliedoveraclosedzone,Green'S functionforapartialdifferentialequationG=a(R, inthreedimensionsisG=l/(4nR(p;q)),relatingvalues ofanditsnormalderivativeO~/On,ifisa

    harmonicfunctionwhichsatisfiestheLaplace'Sequation. Theperturbationpotential(p)atthefieldpointp(x,,

    z1canbeexpressedas

    2

    ()_(

    qrepresentsthesourcepoint(,77,)onthesurface ()=SB(t)USc(t)USF(t),overwhichtheintegrationis performed,andR(p,q)isthedistancebetweenPandg. Surfaces,scandSFaremebodysurface,cavity surfaceandfreesurface,respectively(Fig.5),anditis

    subjecttotheimpermeableboundaryconditionona bOdysurface,

    :.

    (9)

    on

    surface.Theinflowvelocity,,istheresultant velocityoftheadvancevelocity,,andtangential velocity,toxr.

    Dynamicboundaryconditionexpressesthatinvented zone,bladebackpressureisequaltoatmosphere(Fig.6). Fig.6Ventedconditionandpressuredistributioninventedand unventedzones

    AnotherimportantboundaryconditionisKutta condition.Itstatestheequalpressureshouldbesatisfied atthetrailingedge.Eq.f81shouldbediscretizedandthe we~edsurfaceiSdiscretizedintoquadrilateralelements. Then,usingdiscretizedequationandboundarycondition forthenumberofelementsontheweRedsurfaceofthe propeller,potentialsareobtainedoneachelement.By derivativeofthepotential,

    velocityandpressurecanbe

    theperturbationtangential

    determinedfromBernoulli'S

    equation.Finally,thehydrodynamiccharacteristicsofthe propellerareexpressedas

    :

    VA

    _

    cos~

Report this document

For any questions or suggestions please email
cust-service@docsford.com