工程流体力学英文版第三章pdf_资料下载.pdf

工程流体力学英文版第三章pdf_资料下载.pdf

《工程流体力学英文版第三章pdf_资料下载.pdf》由会员分享，可在线阅读，更多相关《工程流体力学英文版第三章pdf_资料下载.pdf（93页珍藏版）》请在冰豆网上搜索。

3.1MethodstoStudyFluidsinMotion1.LagrangianApproach（?

）2.EulerianApproach（?

）3.SystemandControlVolume4.EulerianAccelerationAABBviewpoints:

aindividualfluidparticlebcertainpointinspaceLagrangianDescriptionofMotionisthedescriptionthateveryfluidpartideinflowfieldisobservedasafunctionoftime.Spacecoordinates?

=）,（）,（）,（tcbazztcbayytcbaxx1.LagrangianApproachAABBEulerApproachisthedescriptionthatthemotionfactorsofeveryspacepointinflowfieldareobservedasafunctionoftime.flowfielddescription.Flowfieldmotionfactorsarethecontinuousfunctionsoftimeandspace?

x,y,z?

EulerianDescriptionisutilizedwidelyinengineering.2.EulerianApproach（x,y,z）-EulerianVariables（）（）（）,xyztppxyztVVxyzt?

=?

3.System（?

andControlVolume?

DefinitionofaSystemAsystemreferstoaspecificmassoffluidwithintheboundariesdefinedbyaclosedsurface.ShapemaychangemassnochangeAcontrolvolumereferstoafixedregioninspace,whichdoesnotmoveorchangeshape.Thesurfacesurroundingthecontrolvolumeiscalledcontrolsurface3.System（?

ShapenochangemassmaychangeDefinitionofaControlVolume1?

1?

2?

.Euleriancceleration（）,Vxyzt?

t:

position:

?

tt+:

velocity:

（）,xxyyzz+（）,tVxxyyzzt+?

y?

x?

z?

0?

t?

（x,y,z）?

（）（）（）（）000,lim1lim,limxtttuxxyyzzttuxyztatuuuuuxyztxyztuxyzttxyztutuxuyuzttxtytzt+=?

=+?

000lim,lim,limtttyxzuvwttt=y?

so?

ddxuuuuuauvwttxyz=+and?

ddddddxyzuuuuuauvwttxyzvvvvvauvwttxyzwwwwwauvwttxyz?

or:

（）VaVVt=+?

ijkxyz=+?

Similarly?

Accelerationofparticlesiscomposedoftwoparts?

LocalAccelerationthechangeofvelocityateverypointwithtime.?

ConvectiveAccelerationthechangeofvelocitywithpositionddpppppuvwttxyz=+dduvwttxyz=+Fordensityandpressure:

Generalform:

ddVtt=+?

.TheTotalDerivativeexample3.1velocityis:

2232Vxyiyjzk=+?

（m/s）,Whatistheaccelerationofpoint（3,1,2）.solution:

2220

（2）（3）027xuuuuauvwxyxyyxmstxyz=+=+=22200（3）（3）209yvvvvauvwxyyzmstxyz=+=+=22200（3）02464zwwwwauvwxyyzzmstxyz=+=+=So,theaccelerationofpoint（3,1,2）:

27964aijk=+?

3.2ClassificationofFluidFlowClassificationofFluidFlowBasedontheCharacteristicofFluidBasedontheStateofFlowBasedontheNumberofSpaceVariables1.BasedontheCharacteristicsofFluidIdealflowandViscousflow0or=Incompressibleflowandcompressiblefloworconst=2.BasedontheStateofFlowSteadyflowandunsteadyflow0ort=Rotational（?

）flowandirrotational（?

）flowLaminarflow（?

）andturbulentflow（?

）Subsonicflow（?

）?

Transonicflow（?

）andsupersonicflow（?

）Uniformflowandnon-uniformflow0Vors=?

3.BasedontheNumberofSpaceVariablesOnedimensionalflow（?

）Twodimensionalflow（?

）Threedimensionalflow（?

）4.Steadyflowandunsteadyflowistheflowwhosemotionfactorsdontchangewithtime.Thatis:

SteadyFlow（）,VVxyz=?

0Vt=?

H=C?

Unsteadyflowistheflowthatatleastoneofitsmotionfactorschangeswithtime.ThatisunsteadyFlow（）,VVxyzt=?

0Vt?

H?

51-D,2-Dand3-DFlowOne-dimensionalFlow:

（2）cross-sectionalaveragevaluesSfluidmotionfactorsarefunctionofaspacecoordinate.

（1）Idealflow.（3）motionfactorsarefunctionsofcurvedcoordinatess.（,）xt=（,）xt=（,）st=（,）st=Two-dimensionalFlow:

fluidmotionfactorsarefunctionoftwospacecoordinates.（Notonlylimitedtorectangularcoordinates）.Fluidflowsmotionfactorsarefunctionsofthreespacecoordinates.Forexample:

Waterflowinanaturalriverwhosecrosssectionshapeandmagnitudechangealongthedirectionofflow;

waterflowsaroundtheship.Three-dimensionalFlow:

Apathlineisthetraceafterasingleparticletravelsinafieldofflowoveraperiodoftime.

（1）.DefinitionKinescope1Kinescope2?

3.3Pathline（?

）1.Pathline

（2）?

EquationofPathlineu?

v?

warefunctionsofbothtimetandspace（x?

z）.Heretisanindependentvariabledydxdzuvwdt=AStreamlineisacurvethatshowthedirectionofanumberofparticlesattheatthesameinstantoftime.Thecurveindicatesthevelocityvectorsofanypointsoccupyingonthestreamline.Kinescope2.Streamline1.DefinitionaV?

bV?

cV?

dV?

eV?

EquationofStreamlineSelectpointAinstreamline,dsisadifferentialarclength,uisthevelocityatpointAdsdxidyjdzk=+?

dsuAVuivjwk=+?

Directionalcosinebetweenvelocityvectorandcoordinatescos（,）vVyV=?

cos（,）uVxV=?

cos（,）wVzV=?

Directionalcosinebetweendsandcoordi