Fluid Mechanics (BRUCE R. MUNSON) Chapter3 Elementary Fluid Dynamics-The Bernoulli Equation.pdf

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1、7708d_c03_1008/10/013:01PMPage100mac120mac120:1stshift:Flowpastabluntbody:Onanyobjectplacedinamovingfluidthereisastagnationpointonthefrontoftheobjectwherethevelocityiszero.Thislocationhasarelativelylargepressureanddividestheflowfieldintotwoportions—oneflowingoverthebody,and

2、oneflowingunderthebody.1Dyeinwater.21PhotographbyB.R.Munson.27708d_c03_1018/10/013:01PMPage101mac120mac120:1stshift:3ElementaryFluidDynamics—TheBernoulliEquationAswasdiscussedinthepreviouschapter,therearemanysituationsinvolvingfluidsinwhichthefluidcanbeconsideredasstationar

3、y.Ingeneral,however,theuseoffluidsinvolvesmo-tionofsometype.Infact,adictionarydefinitionoftheword“fluid”is“freetochangeinform.”Inthischapterweinvestigatesometypicalfluidmotions1fluiddynamics2inanele-mentaryway.Tounderstandtheinterestingphenomenaassociatedwithfluidmotion,one

4、mustcon-siderthefundamentallawsthatgovernthemotionoffluidparticles.Suchconsiderationsin-cludetheconceptsofforceandacceleration.WewilldiscussinsomedetailtheuseofNew-ton’ssecondlaw1Fma2asitisappliedtofluidparticlemotionthatis“ideal”insomesense.WewillobtainthecelebratedBernou

5、lliequationandapplyittovariousflows.Al-thoughthisequationisoneoftheoldestinfluidmechanicsandtheassumptionsinvolvedinitsderivationarenumerous,itcanbeeffectivelyusedtopredictandanalyzeavarietyofflowsituations.However,iftheequationisappliedwithoutproperrespectforitsrestriction

6、s,se-TheBernoulliriouserrorscanarise.Indeed,theBernoulliequationisappropriatelycalled“themostusedequationmaybeandthemostabusedequationinfluidmechanics.”themostusedandAthoroughunderstandingoftheelementaryapproachtofluiddynamicsinvolvedinabusedequationinthischapterwillbeusefu

7、lonitsown.Italsoprovidesagoodfoundationforthematerialinfluidmechanics.thefollowingchapterswheresomeofthepresentrestrictionsareremovedand“morenearlyexact”resultsarepresented.3.1Newton’sSecondLawAsafluidparticlemovesfromonelocationtoanother,itusuallyexperiencesanaccelerationo

8、rdeceleration.AccordingtoNewton’ssecondlawofmotion,thenetforceactingonthefluidpart