流体力学英文版复习

Chapter1.FLUIDPROPERTIES第一章流体性质22020/10/29Inphysics,afluidisasubstancethatcontinuallydeformsunderanappliedshearstress,nomatterhowsmallitis.流体是一种一受到切力作用（不论多么小）就会连续变形的物体。Definitionofafluid32020/10/29(1)Density（密度）Densityistheratioofthemassoffluidtoitsvolume.(1.12)Specificvolume(比容):volumeoccupiedbyunitmass.(1.13)Thespecificvolumeisthereciprocal(倒数)ofdensity.(kg/m3)(m3/kg)VmρρmV142020/10/29(2)SpecificWeight（重度）It’stheweightperunitvolume(1.14)inwhichisthespecificweightoffluid,N/m3;Gistheweightoffluid,N.g(1.14a)Ortheproductofdensityandaccelerationofgravityg.VG52020/10/29(3)RelativedensityandspecificgravityTherelativedensity(相对密度)RDofafluidistheratioofitsdensitytothedensityofagivenreferencematerial.refRDThereferencematerialiswaterat4Ci.e.,ref=water.=1000kg/m3dimensionlessquantity无量纲Thespecificgravity(比重)SGofafluidistheratioofitsweighttotheweightofanequalvolumeofwateratstandardconditions(标准状态).waterwaterGGSGdimensionlessquantity无量纲62020/10/29(4)Compressibility（压缩性）Thevolumeoffluidchangesunderdifferentpressure.Asthetemperatureisconstant,themagnitudeofcompressibilityisexpressedbycoefficientofvolumecompressibility(体积压缩系数)p,arelativevariationrate（相对变化率）ofvolumeperunitpressure.pVVpd/d(1.15)Thebulkmodulusofelasticity(体积弹性模量)Kisthereciprocalofcoefficientofvolumecompressibilityp.VVpKp/dd1(1.16)（Pa）（Pa1）72020/10/29Amineraloilincylinderhasavolumeof1000cm3at0.1MN/m2andavolumeof998cm3at3.1MN/m2.Whatisitsbulkmodulusofelasticity?669/3.1100.110(9981000)/10001.510(Pa)pKVVExample1.1Solution:82020/10/29PredominantCause:Cohesionisthecauseofviscosityofliquid.Transferofmolecularmomentumisthecauseofviscosityofgas.(5)ViscosityViscosityisaninternalpropertyofafluidthatoffersresistancetosheardeformation.Itdescribesafluid'sinternalresistancetoflowandmaybethoughtasameasureoffluidfriction.Theresistanceofafluidtosheardependsuponitscohesion(内聚力)anditsrateoftransferofmolecularmomentum(分子动量交换).92020/10/29Newton’slawofviscosityFigure1.5DeformationresultingfromapplicationofconstantshearforceInFig.1.5,asubstanceisfilledtothespacebetweentwocloselyspacedparallelplates（平行板）.Thelowerplateisfixed,theupperplatewithareaAmovewithaconstantvelocityV,aforceFisappliedtotheupperplate.102020/10/29ExperimentshowsthatFisdirectlyproportionaltoAandtoVandisinverselyproportional（反比）tothicknessh.hAVF(1.18)Iftheshearstressis=F/A,itcanbeexpressedashVTheratioV/histheangularvelocityoflineab,oritistherateofangulardeformationofthefluid.112020/10/29(1.19)Theangularvelocitymayalsobewrittenasdu/dz,soNewton’slawofviscosityisTheproportionalityfactor(比例因子）iscalledtheviscositycoefficient（黏性系数，黏度）.FluidsmaybeclassifiedasNewtonianornon-Newtonian.Newtonianfluid:isconstant.(gasesandthinliquids稀液)Non-Newtonianfluid:isnotconstant.(thick稠的,long-chainedhydrocarbons长链碳氢化合物)dudz122020/10/29DynamicviscosityandKinematicviscosity•Thedynamicviscosity（动力黏度）isalsocalledabsoluteviscosity（绝对黏度）.From（1.19）SIunit：kg/(ms)orNs/m2U.S.customaryunit：dynes/cm2（达因秒/厘米2）cgsunit：Poise(P,泊).1P=100cP(厘泊)1P=0.1Pas(帕秒)τdu/dz•Thekinematicviscosity（运动黏度）istheratioofdynamicviscositytodensity.SIunit：m2/sU.S.customaryunit：ft2/s（英尺2/秒）cgsunit：stokes(St,斯).1cm2/s=1St1mm2/s=1cSt(厘斯)Chapter2.FLUIDSTATICS第二章流体静力学142020/10/29BasicequationofhydrostaticsundergravityGravityG(G=mg)istheonlymassforceactingontheliquidfx=0，fy=0，fz=gFigure2.4Avesselcontainingliquidatrest0ρgdpdzrewritingρgdzdpFrom(2.5)cistheconstantofintegration(积分常数)determinedbytheboundarycondition.cgpzintegrating(2.7)152020/10/29gpzgpz2211)(2112zzgppForthetwopoints1and2inthestaticfluidForthetwopoints0and1)(1001zzgppFigure2.4AvesselcontainingliquidatrestThepressureatapointinliquidatrestconsistsoftwoparts:thesurfacepressure,andthepressurecausedbytheweightofcolumnofliquid.162020/10/29Physicalmeaningz——thepositionpotentialenergyperunitweightoffluidtothebaselevel；p/g——thepressurepotentialenergy(压强势能)perunitweightoffluid.Geometricalmeaningz——thepositionheightorelevationhead(位置水头)p/g——thepressurehead(压力水头)perunitweightoffluidSumofthepositionhead(位置水头)andpressureheadiscalledthehydrostatichead(静水头),alsoknownasthepiezometrichead(测压管水头).Theenergyperunitweightoffluidcanbealsoexpressedintermsofthelengthofcolumnofliquid(液柱),andcalledthehead(水头).172020/10/29localatmosphericpressure(当地大气压)paabsolutepressure(绝对压强)pabsghppaabsgaugepressure(表压,计示压强)=relativepressurevacuumpressure(真空压强,真空度)pv,orsuctionpressure(吸入压强),alsocallednegativepressure(负压强)absavppprelativepressure(相对压强)pabsapppghItisusuallymeasuredintheheightofliquidcolumn,suchasmillimetersofmercury(mmHg,毫米水银柱),denotedbyhv.gppgphaabsvvRelatedPressures182020/10/29Localatmosphericpressurep=paCompletevacuumpabs=0AbsolutepressureVacuumpressureGaugepressureFigure2.6absolutepressure,gaugepressureandvacuumpressurepAbsolutepressure2ppa1ppaORelationshipGraph192020/10/29Toavoidanyconfusion,theconventionisadoptedthroughoutthistextthatapressureisingaugepressureunlessspecificallymarked‘abs’,withtheexceptionofagas,whichisabsolutepress