john schroeder - the impact of atmospheric stability on wind structure and turbine wakes as revealed...
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TheImpactofAtmosphericStabilityonWindStructureandTurbineWakesasRevealedby
RadarMeasurements
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JohnL.Schroeder1,JamesB.Duncan2,BrianD.Hirth2,W.ScottGunter3,JerryG.Guynes21GeosciencesDepartment,TexasTechUniversity2NationalWind Institute,TexasTechUniversity3DepartmentofEarthandSpaceScience,Columbus StateUniversity
2016SandiaBladeWorkshop, 31August2016
National Wind InstituteTEXAS TECH UNIVERSITY
ConflictofInterestDisclaimer
Theco-authorsofthispresentationconduct researchintheareaofdocumentingwindplantcomplexflows. ThisresearchissupportedbytheUSDepartmentofEnergy,SandiaNationalLaboratories,theNationalScienceFoundation, andprivateindustry. Severalco-authorsofthis presentation haveequityownership inSmartWindTechnologiesLLC,whichisdevelopingproductsandservicesrelatedtotheresearchbeing reported. ThetermsofthisarrangementareinaccordancewithTexasTechUniversity’sconflictofinterestpolicies.
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PreviousWork:DopplerRadarComplexFlowsDocumentation
• Wakestructureandtracking
• Turbine-to-turbineinteraction
• Arrayedgeeffects
• Terrainimpacts
• Windrampevolution
• Atmosphericstability!
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TechnologyAdvancement
NewDOE-XRadar,ReeseTechnologyCenter
TTUKaMobileResearchRadars
OBJECTIVE:EnhanceClearAirSensitivity/DataAvailability
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InitialDOE-XRadarMeasurementsHighlighttheImpactofAtmosphericStabilityonWindStructure
• Data availability greatly increased with the DOE-X relative to the TTUKa radars.
• Measurements reveal the impact of atmospheric stability on wind structure:
• Unstable “cellular” structure from late morning to evening
• Stable “laminar” structure overnight
• A “streaky” structure appears in between
• Rapid transitions between these different structures
• Significant wind speed and directional shear overnight
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(1) (2) (3)
DOE-XRadialVelocityandTTU200-mTowerTemperature(3) VR (m s-1) – 05/1500 UTC(2) VR (m s-1) – 05/0800 UTC(1) VR (m s-1) – 04/2200 UTC
∆θV= - 1.0KL = -2.7 mIu = 0.35
∆θV = 9.8KL = 8.3 mIu = 0.04
∆θV = -0.8KL = -32.1 m Iu = 0.15
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• Single Doppler sectors• 1.0° elevationtilt• Datacollectedin “clear air”• Instrumented tower nearby• Isolated turbine on edge of farm• Period captures evening
boundary layer transition• 2,821 individual scans collected
during 3 hours 36 minutes• ~4.7 second sector revisit time
Single-DopplerDeploymentwithanInstrumentedTower
DeploymentDetails:
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Single-DopplerRadialVelocityandTowerTemperature
National Wind InstituteTEXAS TECH UNIVERSITY
(1) (2) (3)
Single-Doppler Radial Velocity and Tower Temperature
(3)VR(ms-1)– 0100UTC(2)VR(ms-1)– 2345UTC(1)VR(ms-1)– 2250UTC
∆θV = - 0.7KL = -64.3 mIu = 0.1069
∆θV = 0.5KL = 26.0 mIu = 0.0715
∆θV = 4.3KL = 0.5 m Iu = 0.0177
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• Defineinitialsearch150mbehindturbine’slocation.
• Wakecenterisdeterminedtobethelocationoftheminimumradialvelocityalongthecross-section.
• Utilizingtheinitialwakecenter,thedownstreamboundsaredefinedtosearchforsubsequentwakepositions.
• Processisiteratedoutto3200matintervalsof25m. Howtodefinetheendofthewake?
SimpleWakeDetectionAlgorithm
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• Inorderforthedownstreamradialvelocityfieldtonolongerbeconsideredpartofthewake,werequired:1. Alateralshiftinthewake
centerpointfromthepreviouslocationexceeds50m.
2. Themagnitudeofthevelocitydeficitrelativetotheinflow(200-400mupstream)islessthan30%.
DeterminationofWakeLength
Notperfect!
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StabilityClassification AverageWakeLength(m) NumberofSWPs
Unstable 1265m 242Stable 1792m 915
~42%IncreaseinWakeLengthDuring StablePeriod
Stabilityisdefinedaccordingto:• Monin-Obukhov Length(L)• GradientinVirtualPotential
Temperature(ΔθV).
StableConditions• 0<L <600&ΔθV>0UnstableConditions• -600<L<0&ΔθV<0
DefiningStability
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To denote wake meandering: 1. Fit a linear model to the derived wake centers. 2. Use the variability about this wake center line to quantify
wake meandering.
DeterminationofWakeMeandering
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WakeMeandering
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DeterminingWakeWidth
• Usethewaketrackingalgorithmtofindthecenterline.
• Thewakeedgeisdefinedasthelocationofaninflectionpointalongtheradialvelocitycross-sectionorwheretheaverageoftheendpointsexceed85%ofthefreestreamflow.
National Wind InstituteTEXAS TECH UNIVERSITYWakeWidth
WakeWidth
• Unstable/Convective• Meanwindspeedof
8.40ms-1• MeanTIof0.10
• Stable• Meanwindspeedof
7.35ms-1• MeanTIof0.04
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Summary§ AdvancedDoppler radartechnologies andmeteorological towers(withthermodynamicmeasurements)areusefultoexplorechangesinboundary layerwindstructureandturbinewakecharacteristicswithchangingatmospheric stability.
§Unstableregimes:§ Flowisdominatedbygustsandlulls, rapidchangesinwindspeedanddirection§ Turbinewakelengthsareshorter§ Turbinemeandering ismoresubstantial
§Stableregimes:§ Boundary layergustsandlullssubside, flowbecomesremarkablysmooth§ Shearandveerbecomemoresubstantialwithheight§ TurbinewakelengthscanbecomeVERYlong (e.g.>100D)§Wakemeandering isminimal§ Turbine-turbine interactionisenhanced
§Stableatmosphericconditionsmightbeaneasiertargetforproactivecontrolideasfocusedonminimizing turbine-to-turbine interaction.
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Acknowledgements
FinancialSupport:Single-DopplerdatasetcollectedwithfundingprovidedbySandiaNationalLaboratoriesviatheUSDepartmentofEnergyWindandWaterPowerTechnologiesOffice
DOE-XradardevelopmentandinitialdatacollectionfundedbytheUSDepartmentofEnergy(DE-EE0006804)
Analysisofthesingle-DopplerwakemeasurementswascompletedusingsupportprovidedbyaNationalScienceFoundationGrantCBETaward(1336935)