Review of CFD for wind-turbine wake aerodynamics.pdf

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1、ReviewofCFDforwind-turbinewakeaerodynamicsB.Sanderse∗†,S.P.vanderPijl†,B.Koren†‡AbstractThisarticlereviewsthestateoftheartofthenumericalcalculationofwind-turbinewakeaerodynamics.DifferentCFDtechniquesformodelingtherotorandthewakearedis-cussed.Regardingrotormodeling,recen

2、tadvancesinthegeneralizedactuatorapproachandthedirectmodelarediscussed,asfarasitattributestothewakedescription.Forthewake,thefocusisonthedifferentturbulencemodelsthatareemployedtostudywakeeffectsondownstreamturbines.keywords:windenergy,wakeaerodynamics,CFD,turbulencemodel

3、ing,rotormodeling1IntroductionDuringthelastdecadeswindturbineshavebeeninstalledinlargewindfarms.Thegroupingofturbinesinfarmsintroducestwomajorissues:reducedpowerproduction,duetowakevelocitydeficits,andincreaseddynamicloadsontheblades,duetohigherturbulencelevels.Depending

4、onthelayoutandwindconditionsofawindfarmthepowerlossofadownstreamturbinecaneasilyreach40%infull-wakeconditions.Whenaveragedoverdifferentwinddirections,lossesofapproximately8%areobservedforonshorefarms,and12%foroffshorefarms(seee.g.Barthelmieetal.[1,2]).Whenstudyingpowerlos

5、sesandbladeloading,wind-turbinewakesaretypicallydi-videdintoanearandafarwake[3].Thenearwakeistheregionfromtheturbinetoapproximatelyoneortworotordiametersdownstream,wheretheturbinegeometrydirectlyaffectstheflow,leadingtothepresenceofdistincttipvortices.Tipandrootvorticesle

6、adtosharpgradientsinthevelocityandpeaksintheturbulenceintensity.Forveryhightip-speedratiosthetipvorticesformacontinuousvorticitysheet:ashearlayer.Theturbineextractsmomentumandenergyfromtheflow,causingapressurejumpandconsequentlyanaxialpressuregradient,anexpansionofthewak

7、eandadecreaseoftheaxialvelocity.Inthefarwaketheactualrotorshapeisonlyfeltindirectly,bymeansofthereducedaxialvelocityandincreasedturbulenceintensity.Turbulenceisthedomi-natingphysicalprocessinthefarwakeandthreesourcescanbeidentified:atmosphericturbulence(fromsurfaceroughn

8、essandthermaleffects),mechanicalturbulence(fromthebladesandthetower)andwaketurbulence(fromtipvortexbreak-down).