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《9.Hydraulic forces》由會員上傳分享，免費在線閱讀，更多相關(guān)內(nèi)容在學(xué)術(shù)論文-天天文庫。
1、9HydraulicforcesThepressureriseintheimpellergenerateshydraulicforcesandmomentswhichactontherotor.Inparticularforcesinaxialandradialdirectionaresignificantforappropriatesizingofshaftandbearings.Whiletheradialforceisdeterminedbythepressuredistributionaroundtheimpellercircumference,theaxialforceisg
2、overnedbytheflowthroughtheimpellersidewallgapsandtheresultingpres-suredistributionsontheshrouds.Becauseofitshighrelevanceinthedeterminationoftheaxialforcesactingonturbomachinerotorsthereisawealthofpublicationsdealingwiththesubjectofflowthroughtheimpellersidewallgaps.Acomprehensivecollectionofrel
3、evantquotationscanbefoundin[3.29].9.1FlowphenomenaintheimpellersidewallgapsForreasonsofmechanicaldesign,axialclearancesarerequiredbetweentheshroudsofaclosedimpellerandthecasing(called“impellersidewallgaps”).Widthandshapeoftheresultingliquid-filledspacesbetweenimpellerandcasingareessentiallydeter
4、minedbyaspectsofthemechanicaldesign.Thefluidcontainedintheimpellersidewallgapscannotbeatrestwhentheimpellerrotates:immediatelyattheshroudthefluidadherestothesolidwallandhasthusthevelocitycu=ω×r.Aboundarylayerisformedinwhichthetangentialvelocitydropswithincreasingdistancefromtheshroud.Thefluidals
5、oadherestothecasingwallwherethevelocityiszerocu=0.Thevelocityincreasesinthecas-ingwallboundarylayer,Fig.9.1.WithtightsidewallgapsorlowReynoldsnumbersbothboundarylayersaremerged;withwidegapstheyareseparatedandacoreflowisformed.Theflowintheimpellersidewallgapcanbelaminarorturbulent.Inmostapplicati
6、onswithwaterpumpingtheflowisturbulentandtheboundarylayersareseparatedasde-pictedinFig.9.1;onlythiscaseistreatedinthefollowing.Thecentrifugalforcesintherotatingboundarylayergenerateafluidtransportradiallyoutwards.Thustheshroudactsinasimilarwayasafrictionpump(Chap.3.10.3).Forreasonsofcontinuity,fl
7、uidflowsbackradiallyinwardsalongthecasingwall.Inthemeridionalsectionacirculatingflowisthusestablishedintheimpellersidewallgaps.Figure9.1showsthecorrespondingvelocitydistribu-tionsinradialandcircumferentialdirection.Usuallyth
