propeller design calculation.doc

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1、PropellerdesigncalculationHerewedescribethestepsinasimplepropellerdesigncalculation,usingliftinglinetheory.Atablewithanexampleisgivenafterwards.Thiscorrespondstochapter5.1inMinsaas“PropellerTheory”,butbeawarethattheexampleinchapter5.1haveseveralnumericalerrors,andthedifferentlinesintheexamp

2、letabledon’tnecessarilycomeinorderofcalculation.Thepropellerdesigncalculationconsistsofthreesteps:1.Calculationofthrustandtorque2.Checkofriskofcavitation3.DeterminationofcamberandpitchdistributionCalculationofthrustandtorque1.SelectpropellerdiameterandRPM.ABp-ddiagramorexperiencemightbeused

3、.2.Selectbladesectionthicknessandcamberdistribution,usingforinstancetabulateddatainbookssuchAbbott&vonDoenhoff“Theoryofwingsections”3.Designradialchordlengthdistributionc(r)4.Designradialthicknessdistributiont(r)5.Findradialwakedistributionw(r)frommodeltestsorfromempiricaldata6.Designcircul

4、ationdistribution.Thefollowinggenerictypeofdistributionisfrequentlyused:.Inthiscase,thedesignisaboutselectingvaluesofk,a,andm.7.CalculatemeaninducedtangentialvelocityUTatallradii:8.SolvetofindmeanaxialinducedvelocityUAatallradii9.Findmeanhydrodynamicangleofattackbiatallradii:10.Findcorrecti

5、onfactorsforfinitenumberofbladetodeterminevaluesofUTandUAattheblades.Twoalternativemethods:a.Goldsteinfactors(usedintheexamplebelow)b.Inductionfactors11.Calculate,,and:12.Calculatetheresultingtotalvelocityateachradius:13.Calculatetheliftofeachsection:1.Calculatethecorrespondingliftcoefficie

6、nt:2.Calculatethedragcoefficientofeachsection:3.Calculatethedragofeachsection:4.Calculatetotalthrustofeachsection:5.Calculatetorqueofeachsection:6.Integrate(sumup)tofindtotalthrustandtorque7.Arethethrustaccordingtorequiredthrust?a.No:Gotostep6andadjustthecirculationdistribution.ChangeofRPMo

7、rdiameter,isalsopossible.b.Yes:ProceedtocavitationcheckExamplecalculationCirculationdistributionparameters:k=20a=0.1m=0.4AspreadsheetcontainingtheformulasandnumbersbehindthiscalculationisavailableonthesubjectwebpagesMaininputdata:Vs18knotsT1080kNRPM150n=