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1、ReviewofCFDforwind-turbinewakeaerodynamicsB.Sanderse??,S.P.vanderPijl?,B.Koren??AbstractThisarticlereviewsthestateoftheartofthenumericalcalculationofwind-turbinewakeaerodynamics.Di?erentCFDtechniquesformodelingtherotorandthewakearedis-cussed.Regardingrotormodeling,recen
2、tadvancesinthegeneralizedactuatorapproachandthedirectmodelarediscussed,asfarasitattributestothewakedescription.Forthewake,thefocusisonthedi?erentturbulencemodelsthatareemployedtostudywakee?ectsondownstreamturbines.keywords:windenergy,wakeaerodynamics,CFD,turbulencemodel
3、ing,rotormodeling1IntroductionDuringthelastdecadeswindturbineshavebeeninstalledinlargewindfarms.Thegroupingofturbinesinfarmsintroducestwomajorissues:reducedpowerproduction,duetowakevelocityde?cits,andincreaseddynamicloadsontheblades,duetohigherturbulencelevels.Depending
4、onthelayoutandwindconditionsofawindfarmthepowerlossofadownstreamturbinecaneasilyreach40%infull-wakeconditions.Whenaveragedoverdi?erentwinddirections,lossesofapproximately8%areobservedforonshorefarms,and12%foro?shorefarms(seee.g.Barthelmieetal.[1,2]).Whenstudyingpowerlos
5、sesandbladeloading,wind-turbinewakesaretypicallydi-videdintoanearandafarwake[3].Thenearwakeistheregionfromtheturbinetoapproximatelyoneortworotordiametersdownstream,wheretheturbinegeometrydirectlya?ectsthe?ow,leadingtothepresenceofdistincttipvortices.Tipandrootvorticesle
6、adtosharpgradientsinthevelocityandpeaksintheturbulenceintensity.Forveryhightip-speedratiosthetipvorticesformacontinuousvorticitysheet:ashearlayer.Theturbineextractsmomentumandenergyfromthe?ow,causingapressurejumpandconsequentlyanaxialpressuregradient,anexpansionofthewak
7、eandadecreaseoftheaxialvelocity.Inthefarwaketheactualrotorshapeisonlyfeltindirectly,bymeansofthereducedaxialvelocityandincreasedturbulenceintensity.Turbulenceisthedomi-natingphysicalprocessinthefarwakeandthreesourcescanbeidenti?ed:atmosphericturbulence(fromsurfaceroughn
8、essandthermale?ects),mechanicalturbulence(fromthebladesandthetower)andwaketurbulence(fromtipvortexbreak-down).
