风粗糙度和风切变

RoughnessandWindShear粗糙度和风切变Highabovegroundlevel,ataheightofabout1kilometer,thewindishardlyinfluencedbythesurfaceoftheearthatall.Inthelowerlayersoftheatmosphere,however,windspeedsareaffectedbythefrictionagainstthesurfaceoftheearth.Inthewindindustryonedistinguishesbetweentheroughnessoftheterrain,theinfluencefromobstacles,andtheinfluencefromtheterraincontours,whichisalsocalledtheorographyofthearea.Weshallbedealingwithorography,whenweinvestigatesocalledspeedupeffects,i.e.tunneleffectsandhilleffects,later.在距离地面约1公里的高度，风几乎不受地球表面的影响。然而，在大气的下层，风速受到与地球表面的摩擦的影响。在风能行业中，人们区分地形的粗糙度，障碍物的影响以及地形轮廓的影响，这也称为该地区的地形。当我们稍后研究所谓的加速效应，即隧道效应和山地效应时，我们将讨论山岳学Orography。Roughness粗糙度Ingeneral,themorepronouncedtheroughnessoftheearth'ssurface,themorethewindwillbesloweddown.一般来说，地球表面粗糙度越明显，风速就越慢。Forestsandlargecitiesobviouslyslowthewinddownconsiderably,whileconcreterunwaysinairportswillonlyslowthewinddownalittle.Watersurfacesareevensmootherthanconcreterunways,andwillhaveevenlessinfluenceonthewind,whilelonggrassandshrubsandbusheswillslowthewinddownconsiderably.森林和大城市会显著减缓了风速，而机场的混凝土跑道减缓风速的效果有限。水面比混凝土跑道更平滑，对风的影响更小，而长草，灌木则会使风速大幅减缓。RoughnessClassesandRoughnessLengths粗糙度等级和粗糙度长度粗糙度等级和粗糙度长度的正确定义可在参考手册中找到。术语粗糙度长度实际上是地面以上的距离，其中风速理论上应该为零。Inthewindindustry,peopleusuallyrefertoroughnessclassesorroughnesslengths,whentheyevaluatewindconditionsinalandscape.Ahighroughnessclassof3to4referstolandscapeswithmanytreesandbuildings,whileaseasurfaceisinroughnessclass0.在风能行业中，人们通常会在评估风况时参考粗糙度等级(roughnessclasses)或粗糙度长度(roughnesslengths)。具有许多树木和建筑物的场地一般是3至4的高粗糙度等级，而海面的粗糙度等级为0。Concreterunwaysinairportsareinroughnessclass0.5.Thesameappliestotheflat,openlandscapetotheleftwhichhasbeengrazedbysheep.机场的混凝土跑道的粗糙度等级为0.5。这同样适用于由绵羊放牧的平坦，开阔的场地(如下图所示)。Sheepareawindturbine'sbestfriend.InthispicturefromAkaroaSpit,NewZealand,thesheepkeeptheroughnessofthelandscapedownthroughtheirgrazing.绵羊是风力涡轮机最好的朋友。在这张来自新西兰AkaroaSpit的照片中，通过放牧保持了场地的低粗糙度。TheproperdefinitionofroughnessclassesandroughnesslengthsmaybefoundintheReferenceManual.Thetermroughnesslengthisreallythedistanceabovegroundlevelwherethewindspeedtheoreticallyshouldbezero.粗糙度等级和粗糙度长度的正确定义可在参考手册中找到。术语粗糙度长度实际上是地面以上的距离，其中风速理论上应该为零。WindShear风切变Thisgraphwasplottedwiththewindspeedcalculatoronthenextpage.Itshowsyouhowwindspeedsvaryinroughnessclass2(agriculturallandwithsomehousesandshelteringhedgerowswithsome500mintervals),ifweassumethatthewindisblowingat10m/sataheightof100metres.该图使用下一章节的风速计算器绘制。它向您展示了如果我们假设高度100米处风速10米/秒，那么风速如何在粗糙度等级2(有一些间隔约500米的房屋和篱笆的农田)中变化。Thefactthatthewindprofileistwistedtowardsalowerspeedaswemoveclosertogroundlevel,isusuallycalledwindshear.Windshearmayalsobeimportantwhendesigningwindturbines.Ifyouconsiderawindturbinewithahubheightof40metresandarotordiameterof40metres,youwillnoticethatthewindisblowingat9.3m/swhenthetipofthebladeisinitsuppermostposition,andonly7.7m/swhenthetipisinthebottomposition.Thismeansthattheforcesactingontherotorbladewhenitisinitstoppositionarefarlargerthan