風粗糙度和風切變

RoughnessandWindShear粗糙度和風切變Highabovegroundlevel,ataheightofabout1kilometer,thewindishardlyinfluencedbythesurfaceoftheearthatall.Inthelowerlayersoftheatmosphere,however,windspeedsareaffectedbythefrictionagainstthesurfaceoftheearth.Inthewindindustryonedistinguishesbetweentheroughnessoftheterrain,theinfluencefromobstacles,andtheinfluencefromtheterraincontours,whichisalsocalledtheorographyofthearea.Weshallbedealingwithorography,whenweinvestigatesocalledspeedupeffects,i.e.tunneleffectsandhilleffects,later.在距離地面約1公里的高度，風幾乎不受地球表面的影響。然而，在大氣的下層，風速受到與地球表面的摩擦的影響。在風能行業(yè)中，人們區(qū)分地形的粗糙度，障礙物的影響以及地形輪廓的影響，這也稱為該地區(qū)的地形。當我們稍后研究所謂的加速效應，即隧道效應和山地效應時，我們將討論山岳學Orography。Roughness粗糙度Ingeneral,themorepronouncedtheroughnessoftheearth'ssurface,themorethewindwillbesloweddown.一般來說，地球表面粗糙度越明顯，風速就越慢。Forestsandlargecitiesobviouslyslowthewinddownconsiderably,whileconcreterunwaysinairportswillonlyslowthewinddownalittle.Watersurfacesareevensmootherthanconcreterunways,andwillhaveevenlessinfluenceonthewind,whilelonggrassandshrubsandbusheswillslowthewinddownconsiderably.森林和大城市會顯著減緩了風速，而機場的混凝土跑道減緩風速的效果有限。水面比混凝土跑道更平滑，對風的影響更小，而長草，灌木則會使風速大幅減緩。RoughnessClassesandRoughnessLengths粗糙度等級和粗糙度長度粗糙度等級和粗糙度長度的正確定義可在參考手冊中找到。術語粗糙度長度實際上是地面以上的距離，其中風速理論上應該為零。Inthewindindustry,peopleusuallyrefertoroughnessclassesorroughnesslengths,whentheyevaluatewindconditionsinalandscape.Ahighroughnessclassof3to4referstolandscapeswithmanytreesandbuildings,whileaseasurfaceisinroughnessclass0.在風能行業(yè)中，人們通常會在評估風況時參考粗糙度等級(roughnessclasses)或粗糙度長度(roughnesslengths)。具有許多樹木和建筑物的場地一般是3至4的高粗糙度等級，而海面的粗糙度等級為0。Concreterunwaysinairportsareinroughnessclass0.5.Thesameappliestotheflat,openlandscapetotheleftwhichhasbeengrazedbysheep.機場的混凝土跑道的粗糙度等級為0.5。這同樣適用于由綿羊放牧的平坦，開闊的場地(如下圖所示)。Sheepareawindturbine'sbestfriend.InthispicturefromAkaroaSpit,NewZealand,thesheepkeeptheroughnessofthelandscapedownthroughtheirgrazing.綿羊是風力渦輪機最好的朋友。在這張來自新西蘭AkaroaSpit的照片中，通過放牧保持了場地的低粗糙度。TheproperdefinitionofroughnessclassesandroughnesslengthsmaybefoundintheReferenceManual.Thetermroughnesslengthisreallythedistanceabovegroundlevelwherethewindspeedtheoreticallyshouldbezero.粗糙度等級和粗糙度長度的正確定義可在參考手冊中找到。術語粗糙度長度實際上是地面以上的距離，其中風速理論上應該為零。WindShear風切變Thisgraphwasplottedwiththewindspeedcalculatoronthenextpage.Itshowsyouhowwindspeedsvaryinroughnessclass2(agriculturallandwithsomehousesandshelteringhedgerowswithsome500mintervals),ifweassumethatthewindisblowingat10m/sataheightof100metres.該圖使用下一章節(jié)的風速計算器繪制。它向您展示了如果我們假設高度100米處風速10米/秒，那么風速如何在粗糙度等級2(有一些間隔約500米的房屋和籬笆的農(nóng)田)中變化。Thefactthatthewindprofileistwistedtowardsalowerspeedaswemoveclosertogroundlevel,isusuallycalledwindshear.Windshearmayalsobeimportantwhendesigningwindturbines.Ifyouconsiderawindturbinewithahubheightof40metresandarotordiameterof40metres,youwillnoticethatthewindisblowingat9.3m/swhenthetipofthebladeisinitsuppermostposition,andonly7.7m/swhenthetipisinthebottomposition.Thismeansthattheforcesactingontherotorbladewhenitisinitstoppositionarefarlargerthan