Design and Noise Study of a Low-Drag Wind Turbine for Airborne Power Applications

157 Pages·2017·9.81 MB·English

Design and Noise Study of
a Low-Drag Wind Turbine
for Airborne Power Applica-
tions
A Numerical & Experimental Assessment
B. Van Den Kieboom
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D N S L -D
ESIGN AND OISE TUDY OF A OW RAG
W T A P
IND URBINE FOR IRBORNE OWER
A
PPLICATIONS
A NUMERICAL & EXPERIMENTAL ASSESSMENT
by
B.VanDenKieboom
Forobtainingthedegreeof
MasterofScience
inAerospaceEngineering
attheWindEnergyResearchGroup,FacultyofAerospaceEngineering,DelftUniversityofTechnology,
tobedefendedpubliclyonWednesdayMay10,2017at09:30AM.
Supervisor: Ir.W.A.Timmer TUDelft
Dr.-ing.R.Schmehl TUDelft
Thesiscommittee: dr.ir.B.W.vanOudheusden, TUDelft
MSc.J.Peschel, KitepowerBV
ThisthesisisconfidentialandcannotbemadepublicuntilMay10,2017.
Anelectronicversionofthisthesisisavailableathttp://repository.tudelft.nl/.

Acknowledgments
IcanstillrememberthedayIwalkedintotheofficeofDr.-ing.R.Schmehltoaskforpossiblethesisoptions.
ItoldhimthatIwasinterestedinkitepowerandrotoraerodynamics,andfromthis,hecameupwithoneof
themostinterestingthesistopic(atleastinmyopinion).Iwouldliketothankhimforgivingmethisamazing
opportunityandtobemysupervisorintheinitialphaseofmythesis. BesidesMr. SchmehlIwouldliketo
thankIr.NandoTimmer,forbeingtheexpertonwindturbinedesignduringthisthesisproject,andfortaking
overthesupervisionwhennecessary.
Besidesmytwosupervisors,thisprojectwouldnothavebeenpossiblewithoutthehelpofKitepower.Aspe-
cialgratitudegoesouttoKitepowerforgivingthisthesisprojectmoremeaning.Specialthanksto:Johannes,
Joep,Bert,Roger,Bruno,Antonello,David,Anna,Roland,andBalázstomakethisprojectmoreinteresting
andcreatinganencouragingworkingenvironment. Thankyou,Pietro,tocalculatethepowercurvesfordif-
ferentkiteoptions.IhopemyworkwillhelpaccomplishtobuildthefirstcommercialAWEunit.
Next, IwouldliketothankapersonthatIonlymetoverSkype, butgavemyresearchsomuchmorecon-
tentandpointedmetothefactthatIneedalowdragwindturbine.Thankyou,Rob,foryourinterestingand
valuableopiniononmyworkandsteeringmeinabetterdirection.
Mygratitudegoesouttothepeopleofroom6.08formakingthetimeworkingonmythesissomuchmore
enjoyable,Icouldnotwishforabettergrouptoworkwith. Thankyouforalwayslisteningtomyquestions
andhelpingmewithunderstandingthingsbetterorfindingasolution. Specialthanksto: Pranav,Delphine,
Reynard,Mustafa,Matteo,Ben,Jo,Marcos,Clara,Julia,Ivan,Roberto,Robin,Irene,Viktor,andLuca.
The next group of people I need to thank are all the Belgians, Toine, Mikel, Lucas and Anna to make my
studenttimesomuchmorethanstudying. SpecialthankstoMaarten,Fie,andMichielforproofreadingmy
thesisandforcreatingawesomememoriesduringthis6,5yearsinDelft."ToIndustry..."
And , last but by no means least, I would like to thank the people that are dearest to me. I would like to
thankmyfamily,especiallymyparents,foralwayssupportingmeandhelpingmeoutwheretheycould. Fi-
nally,IwouldliketothankmygirlfriendDeborah,foralwaysbeingthereduringthisthesisandsupportingme.
Thankyou,
BasVanDenKieboom
Delft,May2017
iii

Summary
KitepowerBVisoneofthepioneeringcompaniesthatwantstosucceedintheairbornewindenergyindustry.
Kitepower’sconceptmakesuseofLEIkiteswhichmoveinapumpingcycle,producingenergywhenreeled
out,andconsumingafractionoftheenergywhenreeledin.Tosteerthekite,theymakeuseofakitecontrol
unit(KCU)thatiscurrentlypoweredbybatteries.Thesebatterieslimitflyingtimeto2hoursanditisthegoal
ofthisprojecttocomeupwithasolutiontothisproblem.
ThesolutionchosenbyKitepowerBVistomountasmallhorizontalaxiswindturbineontopoftheKCU
whichwillproduce44Wattofelectricalpower.Duringthisproject,twodesignmethodsarechosentodesign
thiswindturbine. Thefirstisastandardbladeelementmomentumtheory(BEMT)whichisasimpletool
todeterminetheperformanceofawindturbine. Besidesthebladeelementmomentumtheory, asecond
methodwillbeusedwhichisthefreewakeliftingline(LL).Theliftinglinecanbeusedtosimulatedifferent
inflowconditionssuchasyawangles.Itisnecessarytocreateawindturbinewithaminimalamountofdrag
suchthattotalpowerproducedbythekitepowerconceptismaximised,thisissetasthesecondrequirement.
Thelowdragwindturbineisdesignedwiththeuseofaloworderoptimiserwhichtestsallpossibledesignsto
seewhichrotorperformsbest.Thereischosentomaketwodummydesignswhichcanbetestedinthewind
tunneltovalidatethesoftwaresothatKitepowerBVinthefuturecandesigntheirownwindturbines.Atthe
endofthework,afinaldesigniscreatedthatcomplieswiththerequirementsfromKitepowerBV.
Thesmallwindturbineoperatesathighwindspeeds. Becauseofthesehighwindspeeds,thewindturbine
willachievehighrotationalvelocities. Thisrotationalspeedresultsintonalnoises,forthisreason,noiseis
investigated. Withasemi-empiricalmodeldevelopedbyBrooksetal. thesoundpressurelevelofthewind
turbinecanbecalculated.ItusestheoutputconditionsfromtheBEMTorLLcodestocalculatethenoisein
a1/3octavebandfrequency. Theaccuracyofthemodelisvalidatedusingwindtunnelexperimentaldata.
Besidespredictingthesoundpressurelevelclosetothewindturbine,amodelisdevelopedbasedonthework
ofDELTAtoquantifywhatthenoiselevelsareatnoisesensitivelocations. Thewindturbineshouldcomply
withDutchnoiseregulations.
A verification was performed before the wind tunnel test. From this verification, it was found that BEMT
showedgoodagreement,whileLLdoesnotworkforlowReynoldnumberflows.ThisisbecauseoftheKutta-
Jouwkowskyconditionwhichrelatesthecirculationatthec/4linetolift. DuetothelowReynoldsnumber
flow,thebladewillseparateearlierwhichisaviolationoftheKuttacondition.
Duringtheexperiment,itwasseenthattheBEMTresultsagreewiththeexperimentaldata. However,itwas
observedthattheoptimumtipspeedratio(TSR)fortheBEMTislowerthanmeasured.Thishastwopossible
reasons,thefirstisthemethodusedtomeasurethepower.Thesecondreasoncanbethedifferenceinairfoil
polar.Thedragagreesforhigherwindspeedwiththeexperimentaldata.Whileforlowerwindspeedsthereis
alargerdeviation.Thisispossibleduetotheresolutionofthemeasurementequipmentwithacombination
oftheairfoildata.Whenlookingatthenoisedataitwasfoundthatthereareonlytonalpeaksattherotational
frequency. Whenlookingattheshroudedcasetherearenotonalpeaksobserved. Finally,itwasfoundthat
thevalidationbetweenBPMmodelandexperimentalresultisdifficultduetothelargedifferencebetween
datasets. Thisisduetothelackofmeasurementquality. Thenoisemeasurementisnotperformedinan
appropriatetunnelresultinginhighbackgroundnoise. However,similartrendswereobservedbetweenthe
twodatasetsindicatingthatBPMworksbutrequiresmorevalidation.
Thefinaldesignconsistofa12.75cmdiameterrotorwith4blades,whichproducetherequiredpower. The
noisewasinvestigatedat30m/satoptimumTSRanditwasconcludedthatthenoisewillneverbeaproblem
forresidentialareas. Withtheworkperformed,KitepowerBVwillbeabletodesigntheirownwindturbine
basedontheoperatingconditions.
v

Contents
ListofFigures xi
1 Introduction 1
I Background 3
2 ComparisonofPerformance&AeroacousticsModelsforWindTurbines 5
2.1 AirborneWindEnergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 WindTurbinePerformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 BladeElementMomentumTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 LiftingLineTheory(FreeWake) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 VorticesLatticeMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.4 PanelMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.5 ComputationalFluidDynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.6 PerformanceModelSelection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.7 LowReynoldsNumberAirfoils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 FundamentalsofAeroacousticsforWindTurbine. . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 BasicAcoustics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.2 TheoryofAeroacoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 WindTurbineAeroacoustics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.4 Semi-empiricalMethods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.5 ComputationalAeroacoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.6 NoisePropagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.7 DutchRegulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4 WindTunnelExperiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3 ProblemStatement 19
3.1 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
II Methodology 21
4 AerodynamicPerformanceCalculationsModels 23
4.1 BladeMomentumElementTheory(BEMT). . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.1 ActuatorDiskModel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1.2 BladeElementMomentumTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.3 TheBEMTmodelandEngineeringCorrections . . . . . . . . . . . . . . . . . . . . . . 26
4.2 LiftingLineModel(LL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.1 Flowfield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.2 VortexLine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.3 VortexWake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2.4 VortexStrengthCalculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3 AirfoilData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.1 BoundaryLayerTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.2 Xfoil/Rfoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3.3 VerificationofXfoilandRfoil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
vii
viii CONTENTS
4.4 VerificationofBladeElementMomentumTheoryandLiftingLineMethod. . . . . . . . . . . . 40
4.4.1 VerificationoftheNREL5MW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4.2 VerificationoftheSmallWindTurbine. . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4.3 VerificationoftheMiniWindTurbine . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.4.4 ConclusionVerification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5 WindTurbineNoise 45
5.1 TonalNoise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 AirfoilSelf-Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.2.1 TurbulentBoundaryLayer-TrailingEdgeNoise(TBL-TE)&S-SNoise . . . . . . . . . . 46
5.2.2 LaminarBoundaryLayer-VortexSheddingNoise(LBL-VS). . . . . . . . . . . . . . . . . 48
5.2.3 TrailingEdgeBluntnessNoise(TEB). . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.4 TipVortexNoise(TV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3 TurbulenceInflowNoise(TIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.4 TotalNoise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.5 Directivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.6 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.6.1 VerificationofTBL-TENoise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.6.2 VerificationofTEBNoise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.6.3 VerificationLBL-VSNoise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6 AtmosphericAttenuationModel 55
6.1 SphericalSpreading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.2 AtmosphericAbsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.3 ReflectionandWind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.4 LocationofInterest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
III ResultsandDiscussion 61
7 WindTurbineDesign 63
7.1 Optimiser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.2 Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.2.1 FirstOptimisedDesign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7.2.2 SecondOptimisedDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
7.3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.3.1 ManufacturingoftheShroud . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.3.2 ExperimentalTestSet-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.4 InflowAngles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
8 Results 75
8.1 ExperimentalSet-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
8.1.1 TestSet-Up. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
8.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.2.1 MechanicalPower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
8.2.2 Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
8.2.3 TonalNoise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.3 ValidationofSoftware. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.3.1 ValidationPerformanceCodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.3.2 ValidationAirfoilSelf-noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
8.4 FinalRedesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
8.4.1 NoiseoftheFinalWindTurbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
8.4.2 Tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
9 KitePower 99
9.1 PowerProfit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99