TheImpactofAtmosphericStabilityonWindStructureandTurbineWakesasRevealedby

RadarMeasurements

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JohnL.Schroeder1,JamesB.Duncan2,BrianD.Hirth2,W.ScottGunter3,JerryG.Guynes21GeosciencesDepartment,TexasTechUniversity2NationalWind Institute,TexasTechUniversity3DepartmentofEarthandSpaceScience,Columbus StateUniversity

2016SandiaBladeWorkshop, 31August2016

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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

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(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)