Chapter3:Review11.Whatscavitation?cavitationisthephenomenonofcavitygenerationsoftheair,watervaporornothing/vacuuminflowfieldduetopressuredrop.2.Whatscavitatingjet?ajetinwhichthecavitationisartificiallyintroducedormodulatedtoincreasejetimpacterosioncapability.1Review13.Cavitatingjetgenerallyexperiencesthreephases:1)Incipiencyofcavitating;2)Growthofbubbles;3)Collapseofbubblesandgenerationofmicro-jets2Review14.TrueorfalseselectionA)Cavitationhappensonlyinliquid.Onanyoccasion,itwillneverappearintheairorsolidB)Cavitationresultsfromthelocalpressuredrop,andisgenerallyfoundintheflowregionswherestrongturbulenceandvortexintensityexists.C)Cavitationisadynamicphenomenon;Therewontbecavitationinalaminarflow.3Review15.Identifythecavitationmodes:1)Fixedcavitation2)rearflowcavitation3)swirlingcavitation4)shearflowcavitation5)resonatingflowcavitation4Review15.Identifythecavitationmodes:1)Fixedcavitation2)rearflowcavitation3)swirlingcavitation4)shearflowcavitation5)resonatingflowcavitationRequirementpreferableforvorticescombinationandgrowth:a) Helmholtz resonating chamberb) organ-pipe c) self-resonatingItiscalledStrouhalnumber5Review16.Giveainterpretation(翻译,解释)ofthefollowingdefinitionandanalyzethecavitationtendencyindependenceontherighthandparameters.WhentheKislessthan0.5,thejetwouldcavitate6Review17.Trueorfalsechoice(1)thelowertheambientpressure,theeasierthecavitation;(2)thehigherthetemperature,theeasierthecavitation;(3) the higher the relative velocity of the jet, theeasierthecavitation7(4)Gascontent,thenumberofbubbleandtheareaofthecavitatingregion,buttheintensityofthecollapseviolenceofindividualbubble(5)Surfaceintensitywillinhibitcavitation.Review18Review2nExplainthefunctionsofpolymeradditivesonjetcuttingnMicro-mechanismlinearstructureandtheaggregatesofwaterreducetheentrainingofsurroundingfluidnMacro-mechanismmacrostructureentrainslesssurroundingfluidnBombardmentofmacromoleculesontargetmaterialnWhydosomepolymershavenoeffectonjetperformanceatextremelyhighpressurejetting?9Chapter3AdvancedJetCharacteristics-Cavitating,polymersolutionandstar-shapedjetsfor4hours10RoadMapofChapter31.Cavitatingjet2.Polymersolutionjet3.Star-shapedjet111. Cavitating Jet1.1 Definition and general description of cavitation1.2 Cavitation incipiency modes1.3 Cavitation number and parameter effects1.4 Study methods of cavitating jet 1.5 Effect characteristics of Cavitation1.6 General observations on cavitation erosion121.1Definition and General Description of Cavitation 1)Definition:Definedsimplybyphenomena,cavitationisthegenerationandcollapseofair/watervapor/vacantbubblesinflowfield.Intheprocess,violentacousticsoundisproduced.nWhenliquidisheatedtoitsboilingstateorthepressuredecreasedbelowitssaturationvaporpressure,dissolvedgasandvaporintheliquidwillseparateoutandthusbubblesappear.Iftheprocessisresultedfromtemperaturerise,itisusuallycalled“boiling”;whileresultedfrompressuredroporvelocityvariation,theprocessiscalled“cavitation.”132)Phenomena:Cavitationinflowfieldgenerallyexperiencesthreephases:(A)Incipiencyofcavitating(B)GrowthofbubblesCavitatingincipiencyandthebubblegrowthinjetflowaremostcomplicatedprocessanddeterminedbymanyfactors,ofwhichtheratioofambientpressuretothejetpressure,temperature,anddissolvedgasandadditivesdominatetheprocess.Theinitialandtransientregionsarethepotentialareaforcavitatingtooccurwherethepressureislower.1.1Definition and General Description of Cavitation 14A vorticity field in the jet symmetric plane m/sm-1Vd015nJettinginsubmergedmodes,thevortexintensitygenerallyincreasesinshearlayerofjetinitialsection,thenpressureinthecenterofeddieswilldecreasetosomeextent-cavitating(C)CollapsesofbubblesIncavitatingjet,thebubblecollapsemainlyresultsfromtheriseoflocalpressurearounditinfluidflow.nWhenfreejetting,theregionwherepressuregenerallygoesuplittleisatsomestandoffdistance,say(5-10)d0forcavitatingjet,indownstreamoffthenozzleexit.1.1Definition and General Description of Cavitation 16C)CollapsesofbubblesnWhilejettingdownstreamfurtherafterinitialregionofcontinuouswaterjet,vortexintensitywilllowerandcorrespondingpressurewillgoupgradually.-CollapsenForL&Wnozzle,thelocationisabout5-9d0.1.1Definition and General Description of Cavitation 17Micro-jetsGenerationnRiseoflocalpressureinjetflowactsonbubblesimmediately,andleadstodeformationsandrapidcollapsesofcavitationbubbles.nDuringthecollapsingofthebubbles,micro-jetswillbegeneratedoftheintrusionwaterparticleswithextremelyhighvelocity.nThemicro-jets,generallywithrandomdirectionandvelocity,createsaultra-highimpactpressureonasolidtarget,ifthereisoneblockingthewayofjetflow.1.1Definition and General Description of Cavitation 18APossibleCollapseofBubbleandGenerationofMicro-jetCollapse&generatingBubbleDeformationbreakingup&impactingThebubbles,withacertaindegreeofvacuum,areunstableintheirshapes.Waterparticleintrusion193)SomebasicpointsaboutcavitationA)Onlyappearedinliquidfluid.itwillneverappearinairfloworinsolidmoving.B)Cavitationisadynamicphenomenon;Therewontbecavitaioninlaminarflow.C)Cavitationresultsfromlocalpressureloweringinflowfield.Therefore,itcanbecontrolledthroughmodulatingthedegreeofpressuredecrease.1.1Definition and General Description of Cavitation201.2CavitationIncipiencyModes1)Fixedcavitationincipiency2)Rearflowcavitationincipiency3)Swirlingcavitationincipiency4)Shearflowcavitationincipiency5)Resonatingflowcavitationincipiency211)FixedCavitationIncipiencynTheregionwherecavitationoccursfixesinspatial position, generally near a solidsurface.nBecauseofthefluidmixtureorfluidback-flowattheendregionofcavitationarea,bubblemaygrowandcollapsethere.nStrongoscillationwillappearintheregion.FixedcavitationfromlocalpressuredropbecauseofthepropertyofinertialflowC=0.80222)RearflowcavitationincipiencyFlowregimeconversionduringtheflowpassingacurvedboundaryathighspeed232)Rearflowcavitationincipiency(a)Aflowfieldpassingastreamlineobject;(b)Rearflowwithavortexesstreetafterasharpedgedobject;(c)Lowerpressureregionafteraball.242)RearFlowCavitationIncipiencynWhen flowing around a solid object, strongturbulence and vortexes generally appear in therearregionbehindthesolidobjectwithanabruptchangeinitscrossshape.nIn the region transient bubbles may come intobeing, grow, and collapse. Specifically, travelingbubblesmayappearatlow-pressureareanearthesolidsurface,orinthecoreofmovingvortexesinhighturbulentshearinglayer.Whyaremanyobjectsandcreaturesinwaterworldusuallyseeninaformofstreamline?Becauseofthesurvivalofthefittest.253)SwirlingCavitationIncipiencynThisisonetypeofcavitationdetectedearliestbypeoplewithnakedeye.nItalwaysappearsatthetipsofshipspropellersandissometimescalled“tipcavitation”.nOnlywhenthiscavitationbubblecollapsesatornear the solid surface, can strong cavitationerosionhappen.Lowpressureisgeneratedbyhubeddy26TwoTypicalNozzlesbaseduponSwirlingFlowandRearFlowIncipiencySwirlflowcavitationincipiencyrearflowcavitationincipiency27 4) ShearFlowCavitationIncipiencynCavitation,withcontinuousandwidespectrumsofamplitudeandfrequency,characterizesthistype.VortexringCenterofsmalleddywithstrongestvorticitySubmergedjet28 5) ResonationFlowCavi.IncipiencyVortexringCenterofsmalleddySubmergedjeta) Helmholtz resonating chamberb) organ- pipe c) self-resonating29 6) ResonationFlowCavi.IncipiencyWhenresonatingjetismodulatedinafrequencyrangesuitableforthecombinationandgrowthofvortexes,thepulsationwillbehelpfultoexcitestrongcavitationinshearflow.WhentheStrouhalnumbermeetstherequirement:Thevortexwavewillbeself-excitedtoincrease.301.3CavitationIndexandParameterEffectsCavitationnumber:anindexofprobabilityandextentthatcavitationappears.Forjet:Pa:ambientpressure,Pv:vaporizingpressure;Vj:jetvelocityrelativetoambientflow.nWhenthecavitationbeginstohappen,K=Ki,namedcavitationincipiencynumber;nwhenthecavitationfurtherdevelops,K2x104,thetwovaluesareapproximatelythesame.2.4 Drag-reducing Functionp4x103Re2x104,thefrictionfactorismuchsmaller.pRe4x103,thefrictionfactorisgreater.622.4Drag-reducingFunctionPressuredropdataforflexlance(100ftxinch)fittedwith0.6mmdiametertipnozzle 63Dragcoefficientofaball-aninterestingphenomenonWhichisbigger?642.5MoleculeStructuresSufferBreakageatHighSpeedFlow.Center-linemeanvelocityattenuationofsurfactantsolutionjetsatdifferentRe.Viscousflowcharacterizesthelowspeedflow;Inertialflowcharacterizesthehighspeedflow.652.6 Types of Applications of SUPER-WATER SUPER-WATER increases the efficiency of high-pressure water blasting in: cleaning descaling 除垢除垢 lancing切切割割 decontamination 排污排污 underwater operations drilling cutting fracturing 破碎、破碎、压裂663 Star-shaped Jet(星形喷嘴射流星形喷嘴射流) 3.1 Background/purpose3.2 Comparison research method3.3 Nozzle design3.4 Experiment methods3.5 Experiment results3.6 ConclusionTo give out a method of jet research673.1 Background 3.1 Background 1.Before 1990 the research efforts on water jet nozzles focused mainly on round ones specifically in contraction mode, surface finish and the modul-ation of desired jet performance. The theory and applications of round jets are rather complete and common. 683.1 Background 3.1 Background 2. But the round jets are not absolutely more efficient over other shaped ones especially at high pressure.3. In recent years some new nozzles with noncircular exit cross sections have shown their high efficiency in water jet cleaning industry.693.2 Comparison Research MethodUnder two conditions:1. In Non-submerged mode：to measure standoff distance of incipiency of atomization2. In submerged mode： to measure velocity field703.3 Nozzle DesignPrinciples：1）Only change to the star-shaped nozzle is to be made in the shape of cross section of exit section, with other parameters equal to those of round nozzle;2）Cross section of nozzle exit is to be axisymmetric.713.3 Nozzle Design Cross section area of the star-shaped nozzle：Schematic of the star-shaped nozzle:723.3 Nozzle DesignNozzle parameters typeEntr.ID/mmCA /oEx.L/mmMax.Dn/mmMin.Dn/mmEql.Dn/mmDisc.Coo1820186660.98*182018113.65.970.98733.4 Experiment Methods In non-submerged mode： Two nozzles are connected in parallel to a symmetrically designed upstream entrance pipes, and the tests are conducted simultaneously. 743.4 Experiment Methods In submerged mode： with PIV (Particle Image Velocimeter) technology，measuring velocity fields of the two nozzle jets at common both upstream and downstream flow conditions, including exit velocity, confining mode etc. 753.4 Experiment Method763.5 Results Comparison in AirIn (10-100）d0 for the star-shaped jet ，the diameter is almost the same with no increase .Starshapednozzleroundnozzle77The initial section is much longer.3.5 Comparison in AirStarshapednozzleroundnozzle78Condition：exit velocity is 15m/s，corresponding Re is 4104Confining pipe diameter is 110 mm that is far greater than the nozzle diameter 3.5 Exp. In Submerged Mode79velocity field for the round jet: SOD = (0-7)de 3.5 Comparison in Submerged Mode80Flow field of * jet on the short axis plane:SOD = (0-7)de 3.5 Comparison in Submerged Mode81Flow field of * jet on the long axis plane:SOD = (0-7)de 3.5 Comparison in Submerged Mode823.5 Comparison of Centerline VelocityStarshaperounddimensionlessstandoffdistancedimensionlessVc833.5 dynamic pressure and velocity on centerline Dyn.PM.Vdimensionlessstandoffdistancecontrasttoroundjet843.6conclusion1.Whenjettinginairthestar-shapednozzlecangreatlyincreasejetfocusingorinitialflowlength,thenismorepreferableincleaningandcutting.2.Whenjettinginsubmergedmodethestar-shapednozzleincreasevelocityanddynamicpressureoncenterlineby20and45percentrespectivelyinstandoffdistancerange6-14de.85Homework21.Inwaterjetting,polymerscanbeusedtoinhibitwaterjetfromatomizationandthenmakethejettinglonger.Pleasedescribethemicro-mechanismsforpolymertofunctionandselectpolymeraccordingly.2.Pleasegiveouttheformulatocalculatecavitationnumberofawaterjet,andanalyzetheinfluenceofthefactorsonjetcavitating.86