通过应用分散器中的导叶改善轴流式风机的性能外文文献翻译、中英文翻译

附录A通过应用分散器中的导叶改善轴流式风机的性能平行壁无叶分散器中的流程得到离心式风机和压缩机的广泛应用，其本质是在很大程度上是由强森调查并描述的。他在无叶片的空间展示了歪曲界面层的发展和旋转失速的存在。这些现象也出现在用于混杂流动机器的圆锥形环型分散器中。在这种情况下，旋流以及由此产生的垂直于分散器壁的体积力(参见图1)，会在中心端凸墙附近产生一个静压力，这个静压力要低于侧凹墙上产生的静压力。它与壁面摩擦力一起导致在中心端墙壁附近产生一个低能源区域，并且逆流一定发生在分散器的中心端。这种不利的气流会导致很低的分散效率和不稳定的气流，例如叶轮和分散器中的旋转失速。图1.轴流式风机的体积力分散器导叶位于导流罩上并通过半个径向无叶分散器通道，Yoshinaga等人将其应用于高比转速离心压缩机。他们获得了改善的压力恢复和通过分散器通道的等速流。最近，Sitaram和Issac[4]采取了一种相似的方法，但是从辐形分散器的插孔边应用了部分高度导叶。这项研究研究了一系列导叶高度，其百分比是0%(无叶片的分散器)，20%，30%，40%和100%(满叶分散器)。他们表示，与无叶片的分散器比较，20%高度导叶的应用提高了高峰能量系数并改善了操作范围。要矫正轴流式分散器中不利气流，Sakai等调查了一台式样分散器，其低度导叶附着在中心墙壁上。这次调查显示，导叶的应用能有效的压制气流逆转的发展。当前实验性调查用来寻找界面层叶片理想的数量和最佳的地点以得到轴流式通风机的最佳性能。高度为5mm(分散器通道深度的20%)的导叶位于在圆锥形环型分散器的中心。叶片被设计成一条恒定角度为30°、厚度为1.0mm的对数螺线。性能测试和详细的分散器气流测量能确定(a)叶片的最佳数量，(b)导叶的最佳位置，并且(c)可以在改善设计方面加强对内部流场的理解。测试设备如图2。用于此次研究的是一台具体速度Ns=0.96的轴流式风机。为获得在分散器的轴对称流，用一蓄电池室代替正常的收集蜗壳，并且通过调整72个槽孔可以得到不同的空气质量流量。叶轮和分散器的基本设计规格如下：叶轮出口插孔墙壁和圆锥环形分散器椎体角度a=60º叶轮入口桨叶角（计量从子午圈方向）b=50º叶轮出口桨叶角（计量从子午圈方向）bi=30º平均半径叶轮出口ri=0.10m平均半径分散器出口r2=0.25m分散器通道深度b1=b2=26mm刀片数量12图2.各部位名称图3.内部流动测量站（5导叶）导叶的设计在锥形表面上提供了一个30º常数螺旋角和一5mm（大约分散器深度的20%)的高度。导叶位于圆锥形环型分散器的插孔边，其入口半径比为1.05，出口半径比为2.0。对于供选择的设计分离机叶片其入口半径比1.4或1.6。测试风机的入口压力被视为高压水龙头的均值，位于四条直径逆流叶轮和二条直径顺流流程直挺器。对于分散器入口和排放条件的测量，分散器导流罩和中心墙壁上装有10个高压水龙头，半径为R=1.1和R=2.0。静压就是通过这十个压力读数的平均值评估得到估计。对于分散器中详细气流的测量，沿着图3中显示的线和点制作了三孔眼镜蛇型偏航探头。偏航探头由0.7mm不锈钢管做成的，并且探针的最大投影面积大约是通道气流区域的0.3%。有人认为，探针对流场的影响是很小的。从显示的每半径比的侧墙上安装探头，并且通过转动中心墙修改周围环境，就是相对探头移动了叶片通道。对于压力测量，需要一台压力传感器。结果讨论对风机和分散器性能的第一次研究是为了确定全长导叶的最宜数量，从入口半径比1.05延长到出口半径比2.0.后来这项研究被扩大包括分散器出口区域的短分散叶片；这些叶片从进口半径比1.4或1.6延长到出口半径比2.0.对风机和分散器性能的第一次研究是为了确定全长导叶的最宜数量，从入口半径比1.05延长到出口半径比2.0.后来这项研究被扩大包括分散器出口区域的短分散叶片；这些叶片从进口半径比1.4或1.6延长到出口半径比2.0.5,11和17导叶的轴流式风机的基本性能与图4中的无叶分散器的差不多。上横坐标表示的是流程角（从正切方向测得）和入射角（入射角被定义为空气角减去叶片角）。在无叶片空间中假定一个叶轮滑动系数和常数气流角，从叶轮出口气流条件可计算出气流角。滑动速度和滑动系数的计算是基于Wiesner的相关理论，适当修改轴流式风机以允许非径向排出。图4.行程压力系数图5.叶轮压力系数图6.分散器效率（无叶分散器）图7.速度径向分量的分布叶轮的相关压力系数由风机入口和分散器入口的压力差异计算得到。对于无叶分散器，叶轮压力系数的峰值出现在气流系数0.32.无叶分散器获得的级压力系数显示的流量系数峰值大约为0.4，并且显然叶轮和无叶分散器的特点没有得到很好的匹配。分散器中导叶的结构影响叶轮气流条件，并将叶轮峰值压力系数降低到大约0.29，而没有明显的改变其大小。行程压力系数的大小由于导叶的应用而增加，峰值也在气流系数大约为0.32时出现，因此就能更好的和叶轮匹配。11和17叶轮的应用导致在很宽的工作范围内出现高压系数。图6中显示了各个分散器效率。分散器效率由分散器中实际和理论静态压力增长率来定义，公式为v1表示分散器进口速度，根据上面描述，其值通过叶轮出口的滑动系数和分散器的常数气流角估算得到。分散器效率的估算受流量系数的限制，在分散器进口并未出现逆流，当逆流存在时效率的定义就不再是有意义的。对于无叶分散器，效率呈线性增加，流量系数也从0.3增加到0.4。之后效率基本保持不变，流量系数则继续增加。低流量系数区域的低效率是由于分散器中心墙附近的逆流造成的。这个逆流区导致分散器很大堵塞，因此可以有效的阻止速度的减少。随着流率的增加，逆流区域下降，不再存在0.38的流量系数。无叶分散器因此需要逆流才能运行，在这个气流范围内，叶轮给出了峰值压力增长值(如图5)。11和17式导叶的引用提高了分散器在整个气流范围内的效率（如图6）。而在0.25到0.35的低流量系数范围内这种提高更明显，同时整个过程中压力系数的增高也能反映这种提高（如图4）。在0.4以上的高流量系数范围内，当使用无叶分散器时行程压力系数是最大的（如图4）。这是由于在高流量区域内叶轮性能更好（如图5）。增加流量入射角成负增加，而分散器效率（如图6）线性增加。但是入射角是基于一维分析，只给定了平均角；它没有反映出导叶实际的入射角。零入射角时的流量系数要比通过一维流角估计的大，因为在半径比为1.0到1.1的无叶通道内扭曲的边界层会继续延伸。图9.速度矢量分布（f=0.32，距离中心孔墙壁2mm）图8中显示了5叶和11叶分散器上总压系数Cpt在垂直于中心孔墙壁和一系列不同半径比的平面上的分布。在此横截面上，集流器和导流罩都呈圆弧状，但是在这里我们将其设为矩形网格。总压系数Cpt为局部总压比。总压力通过三洞眼镜蛇探头在测量。随着半径比的增加，在流量系数为0.26的情况下，在叶片的凹侧（图8中叶片的右边）就会出现一个低能区域。这个低能区域的中心位于叶片离中心孔墙壁高度的1.5倍的位置，即半径R=1.3.这个低能（低总压系数）区域不会出现在叶片的凸侧，它是由中心孔墙壁附近的高切向流形成的。当这个小角气流通过叶尖时，它从叶片中分离出来，低能尾迹也会有所发展。提高叶片数量会降低尾迹的程度，提高能量。低能尾迹不会通过提高叶片数量来消除。但是11叶片设计优于5叶片设计。为了获得导叶的最佳位置，就要考虑5叶和11叶风机中心孔墙壁附近的气流分布。图9a和9b显示了流量系数Φ=0:32时，距离中心孔墙壁2mm的圆锥形环节上的速度分布。图10.行程压力系数图9a和9b中显示了由于中心孔墙壁附近的扭曲的边界层的发展，随着气流通过分散器速度就会趋于切向。5导叶分散器入口处的气流几乎是沿着导叶的，但是在低气流区，少量导叶不能纠正倾斜流。基于这些发现，就要考虑分割叶片，见图9c和9d。分割叶片的高度、厚度和安装角与全叶形的相同。尽管增加叶片数量会导致摩擦损失，但是考虑到改善气流导向会导致整个性能的提高。具有分割叶片的设计的风机的性能与具有11全叶的风机和不具叶片的风机相比，见图10.分割叶片设计的应用导致了在流量系数上有相当大的改善，表明在低流量系数条件下稳定性提高了。正梯度向低流量方向移动。这种风机性能的改善是由于当引入分割叶片设计时分散器效率的提高，见图11.在低流量系数区域分散器效率就会获得相当的改善。四种典型的分散器的速度vm径向分量在流量系数为f=0.26时的分布，见图12.这显示了导叶间速度分布（见图3中线C）。没有导叶，中心墙附近由逆转气流引起的气流通道的阻塞就会更严重，因此限制了风机的流量范围。5导叶风机中，从半径比为1.5到分散器出口都存在着逆流（见图12b）。虽然11导叶风机中没有逆流，但是Vm在分散器出口就会变得非常小，且接近圆周方向。这个圆周方向的气流导致了叶片凹侧附近产生了一个低能区（见图8）。这个位于下游区叶片间的气流也会产生阻碍，但是其范围远比设计无导叶风机时小的多。分割叶片是应用导致中心孔墙壁附近气流分布的进一步提高。这也就会导致低流量系数时分散器的更高的效率，增大风机的运行范围。图12.速度径向分量的分布基于对轴流式风机分散器通道的性能测试和详细的气流测量，得出以下结论：（1）.通过安装导叶分散器气流结构得到改善，并且分散器效率也得到大大提高。（2）.为提高机器在较广范围内的性能和气流的稳定，已确定其最佳数量和最适宜的安排。（3）.通过对分散器通道中的气流结构进行了准备的测量，纠正了通过导叶调整逆流和不稳定气流的过程。附录BPerformanceimprovementofaaxialfanthroughtheapplicationofguidefencesinthevanelessdiffuserThenatureoftheflowintheparallelwalledvanelessdiffuser,commonlyadoptedforcentrifugalfansandcompressors,wasextensivelyinvestigatedanddescribedbyJansen[1,2].Heshowedthedevelopmentoftheskewedboundarylayerandtheexistenceofrotatingstallinthevanelessspace.Thesephenomenaalsooccurintheconicalannulardiffuserformixed-flowmachines.Inthiscasetheswirlingflow,andtheresultantbodyforcenormaltothediffuserwalls(seeFig.1),producesastaticpressurenearthehub-sideconvexwallwhichtendstobelowerthanthatontheshroud-sideconcavewall.This,togetherwithwallfriction,leadstothedevelopmentofalow-energyregionnearthehub-sidewall,andflowreversalisliabletooccuronthehub-sideofthediffuser.Thisunfavourableflowcausespoordiffusereffectivenessandunstableflow,suchasrotatingstall,intheimpelleranddiffuser.Fig.1BodyforceintheaxialfandiffuserYoshinagaetal.[3]applieddiffuserguidevanes,fromtheshroud-sideandacrosshalfofthepassageoftheotherwiseradialvanelessdiffuser,toahighspecificspeedcentrifugalcompressor.Theyobtainedimprovedpressurerecoveryandamoreuniformflowacrossthediffuserpassage.Morerecently,SitaramandIssac[4]adoptedasimilarapproachbutappliedthepartialheightguidevanesfromthehubsideoftheradialdiffuser.Inthisstudyarangeofguidevaneheightswereinvestigatedsuchthatthepercentageofvaneheightwas0(vanelessdiffuser),20,30,40and100percent(fullyvaned).Theyshowedthattheapplicationof20percentheightguidevanesledtoanincreaseinthepeakenergycoefficientandanimprovedoperatingrangewhencomparedtothevanelessdiffuser.Torectifytheunfavourableflowinthemixed-flowdiffuser,Sakaietal.[5]investigatedamodeldiffuserwithlowheightguidefencesattachedtothediffuserhubwall.Thisinvestigationshowedthattheapplicationofguidefenceswaseffectiveinsuppressingthedevelopmentofflowreversals.Thepresentexperimentalinvestigationwasdesignedtofindtheidealnumberandbestlocationoftheboundarylayerfencesinordertoobtainoptimumperformanceofaaxialfan.Theguidefences,whichhaveaheightof5mm(20percentofthediffuserpassagedepth),wereplacedonthehubsideoftheconicalannulardiffuser.Thefencesweredesignedasalogarithmicspiralwithaconstantangleof30andathicknessof1.0mm.Theperformancetestsanddetaileddiffuserflowmeasurementswerecarriedouttoascertain(a)themostfavourablenumberoffences,(b)thebestlocationoftheguidefencesand(c)animprovedunderstandingoftheinternalflowstructurewithaviewtoimproveddesigns.ThetestfacilityisshowninFig.2.ForthisinvestigationaaxialfanwithaspecificspeedNs=0.96wasused.Toobtainaxisymmetricflowinthediffuserthenormalcollectingvolutewasreplacedwithanaccumulatorchamber,andtheairmassflowratewasvariedbyadjusting72slotsonthesideofthechamber.Thebasicdesignspecificationoftheimpelleranddiffuserwasasfollows:Coneangleofimpellerexithubwallandconicalannulardiffusera=60Impellerinletbladeangle(measuredfrommeridionaldirection)b=50Impellerexitbladeangle(measuredfrommeridionaldirection)bi=30Meanradiusofimpellerexitri=0:10mMeanradiusofdiffuserexitr2=0:25mDepthofdiffuserpassageb1=b2=26mmNumberofblades12Fig.2ExperimentalarrangementFig.3Internalflowmeasurementstations(fiveguidefences)Thedesignoftheguidefencesprovideda30ºconstantanglespiralonthedevelopedsurfaceoftheconeandaheightof5mm(thisisapproximately20percentofthediffuserdepth).Theguidefenceswereplacedonthehubsideoftheconicalannulardiffuserfromaninletradiusratioof1.05toanexitradiusratioof2.0.Foralternativedesignssplitterfenceswereincludedwithaninletradiusratioof1.4or1.6.Theinletpressureofthetestfanwastakenastheaveragedvalueoftwopressuretaps90ºapart,locatedfourdiametersupstreamoftheimpellerandtwodiametersdownstreamofaflowstraightener.Forthemeasurementofthediffuserinletanddischargeconditionstenpressuretaps(AtoEinFig.3)werelocatedatradiiofR=1.1and2.0ontheshroudandhubwallsofthediffuser.Thestaticpressurewasevaluatedthroughthemeanvalueofthesetenpressurereadings.Forthemeasurementofthedetailedflowinthediffuser,three-holecobra-typeyawprobetraversesweremadealongthelinesandatthepointsshowninFig.3.Theyawprobewasmadefrom0.7mmstainlesssteeltubesandthemaximumprojectedareaoftheprobewasapproximately0.3percentofthepassageflowarea.Itwasconsideredthattheinfluenceoftheprobeontheflowfieldwassmall.Theprobewasinstalledfromtheshroud-sidewallateachradiusratioshownandthecircumferentiallocationwasalteredbyrotatingthehubwall,whichmovedthevanedpassagerelativetotheprobe.Forpressuremeasurementasinglepressuretransducer,witharangeof0–250mmofwater,wasusedwithascanivalveandaveragedmagnitudesobtained.Thefananddiffuserperformancewasfirstinvestigatedtoascertaintheoptimumnumberoffull-lengthguidefences,extendingfromaninletradiusratioof1.05toadischargeradiusratioof2.0.Theinvestigationwasthenenlargedtoincludeshortsplitterfencesinthedischargeregionofthediffuser;theseextendedfrominletradiusratiosof1.4or1.6tothedischargeradiusratioof2.0.Thebasicperformanceoftheaxialfanwith5,11and17guidefencesiscomparedwiththatwiththevanelessdiffuserinFig.4.Alsoshownastheupperabscissaistheflowangle(measuredfromthetangentialdirection)andincidenceangleontotheguidefence(theincidenceangleisdefinedastheairangleminusthebladeangle).Theflowanglewascalculatedfromtheimpellerexitflowconditionsassuminganimpellerslipfactorandaconstantflowangleinthevanelessspace.ThecalculationoftheslipvelocityandslipfactorwasbasedonthecorrelationbyWiesner[6],suitablymodifiedforthemixed-flowmachinetoallowforthenon-radialdischarge.Fig.4StagepressurecoefficientFig.5PressurecoefficientoftheimpellerFig.6Diffusereffectiveness(Vanelessdiffuserwithoutfence)Fig.7Distributionofthemeridionalcomponentofvelocity(With11guidefences)Fig.8DistributionofthetotalpressureratioCpt(f=0.26)Thecorrespondingpressurecoefficientoftheimpeller,whichwasevaluatedfromthepressuredifferencebetweenthefaninletanddiffuserinlet(R=1:1),isshowninFig.5.Forthecasewiththevanelessdiffuserthepeakimpellerpressurecoefficientoccursataflowcoefficientof0.32.Thestagepressurecoefficientobtainedwiththevanelessdiffusershowsapeakataflowcoefficientofapproximately0.4(Fig.4),andclearlytheimpellerandvanelessdiffusercharacteristicsarenotwellmatched.Inclusionoftheguidefencesinthediffuserinfluencedtheimpellerflowconditionsandshiftedtheimpellerpeakpressurecoefficienttoareducedflowrateofapproximately0.29,withoutsignificantlychangingthemagnitude(seeFig.5).Themagnitudeofthestagepressurecoefficientwasincreasedbytheapplicationoftheguidefences,andthepeakoccurredataflowcoefficientofapproximately0.32,therebyprovidinganimprovedmatchwiththeimpeller.Theapplicationof11and17guidefencesledtoahigh-pressurecoefficientoverabroadoperatingrange.TheeffectivenessofeachdiffuserdesignisshowninFig.6.Diffusereffectivenesswasdefinedbytheratioofactualandtheoreticalstaticpressureincreaseinthediffuser,givenbywherev1isthediffuserinletvelocity,evaluatedthroughtheslipfactorattheimpellerexitandconstantflowangleinthediffuserasdescribedabove.Evaluationofthediffusereffectivenesswaslimitedtoflowcoefficientswherereverseflowatthediffuserinletdidnotoccur;whenreverseflowexiststhedefinitionofeffectivenessceasestobemeaningful.Forthevanelessdiffusertheeffectivenessincreasedlinearlyastheflowcoefficientincreasedfrom0.3to0.4.Itthenremainedapproximatelyconstantastheflowcoefficientwasfurtherincreased.Thepooreffectivenessatthelowflowcoefficientswasduetoreverseflownearthehubwallofthediffuser.Thisreverseflowregioncausedasignificantblockageinthediffuser,therebypreventinganeffectivereductioninvelocity.Astheflowratewasincreasedthemagnitudeofthereverseflowregiondecreasedandceasedtoexistataflowcoefficientof0.38.Thevanelessdiffuserthereforeoperatedwithreverseflowovertheflowrangeatwhichtheimpellergavethepeakpressurerise(seeFig.5).Theintroductionof11and17guidefencesledtoanimprovementinthediffusereffectivenessoverthefullflowrange(Fig.6).Theimprovementatlowflowcoefficients,intherange0.25to0.35,wasparticularlymarkedandwasreflectedinasignificantimprovementinthepressurecoefficientforthecompletestage(Fig.4).Athighflowcoefficients,inexcessof0.4,thestagepressurecoefficientwaslargestwhenthevanelessdiffuserwasused(Fig.4).Thiswasduetothebetterperformanceoftheimpelleratthehighflowrates(seeFig.5).Thediffusereffectiveness(Fig.6)increasedlinearlyastheincidenceanglebecamelessnegativewithincreasingflowrate.Theincidenceangle,however,isbasedonaone-dimensionalanalysisandgivesameanangleonly;itdoesnotrepresenttheactualincidenceontotheguidefence.Theflowcoefficientforactualzeroincidenceislargerthanthatevaluatedfromtheone-dimensionalflowangleasaskewedboundarylayerdevelopsinthefencelesspassagebetweenradiusratiosof1.0and1.1.Fig.9Distributionofthevelocityvector(f=0.32,2mmfromthehubwall)ThedistributionofthetotalpressurecoefficientCptontheplanenormaltothehubwallandataseriesofradiusratiosisshowninFig.8fordiffuserswith5and11guidefences.Inthiscross-sectionthehubandshroudwallsarecirculararcs,buttheyareillustratedhereasarectangularmesh.Cptwasevaluatedastheratiooflocaltotalpressure.Thetotalpressuresweremeasuredbyathree-holecobraprobe.Astheradiusratioincreased,foraflowcoefficientof0.26,alow-energyregiondevelopedneartheconcavesideofthefence(thisistheright-handflowcoefficientof0.26,alow-energyregiondevelopedneartheconcavesideofthefence(thisistheright-handsideofthefenceshowninFig.8).Thecentreofthislow-energyregionwaslocatedatabout1.5timesthefenceheightfromthehubwall,atR=1.3.Thislow-energy(lowCpt)regionwasnotobservedontheconvexsideofthefence.Thelow-energyregionwasgeneratedbythehighlytangentialflownearthehubwall.Whenthissmallangleflowpassesoverthefencetipitseparatesfromthefenceandalow-energywakedevelops.Increasingthenumberoffencesreducedtheextentofthewakeandtheenergylevelincreased.Thelow-energywakewasnoteliminatedbyincreasingthefencenumber.The11fencedesignwas,however,superiortothe5fencedesign.Inordertoobtainthemostappropriateguidefencelocationthedistributionoftheflownearthehubwallfor5and11fenceswasconsidered.Thevelocitydistributiononaconicalsection2mmfromthehubwallisshowninFigs9aandbforaflowcoefficientΦ=0:32.Fig.10StagepressurecoefficientThesefigures,Figs9aandb,showthatthevelocitybecomesmoretangentialastheflowpassesthroughthediffuserduetothedevelopmentofaskewedboundarylayernearthehubwall.With5guidefencestheflowintheinletregionwasalmostalongthefences,butinthedownstreamregion,thesmallnumberoffencescouldnotrectifytheskewedflow.Basedontheseobservationsasplitfencearrangementwasconsidered(seeFigs9candd).Theheight,thicknessandsettingangleofthesplitterfenceswerethesameasthoseforthefullfencetype.Althoughtheincreasednumberoffenceswouldleadtoincreasedfrictionlossitwasconsideredthattheimprovedflowguidancewouldleadtoanoverallimprovementinperformance.Thebasicperformanceofthefanwiththesesplitterfencedesignsiscomparedwiththatobtainedwith11fullfencesandwithnofencesinFig.10.Applicationwiththesplitterfencedesignsledtoconsiderableimprovementinthepressurecoefficientandshowedimprovedstabilityatlowflowrates;Thepositivegradientdomainmovedtowardsareducedflowrate.ThisimprovedfanperformanceisattributedtotheimproveddiffusereffectivenessshowninFig.11whenthesplitterfencedesignswereintrodu