(6.4)--Chapter 6 Flow in Pipes - P4流体力学环境水力学.ppt

§6–4FrictionalLossinPipelineFrictionresistanceisthereasonthatcausesthefrictionhead(pressure,energy)loss.Darcysformulaisusedtocalculatethefirctionloss,butthecoefficientoffrictionresistanceneedstodiscussdeeply.

Nikuradsedaubedthesandswhichhadbeensiftedtohavethesamediametersontheinnerwallofpipelinewithdifferentdiameterstomakeamanualroughpipelinetodoexperiment.Reynoldsnumberofexperimentrange,relativeroughness,theexperimentalcurveisshowninFigure.1.Nikuradseexperiment§6–4FrictionalLossinPipeline

FigureNikuradseexperimentalcurve§6–4FrictionalLossinPipeline

SeefromFigure6—12,therelationof,andcanbedividedfivedifferentzone,thechangingrulesofitis:(1)LaminarflowzoneAs,allexperimentalpointsconcentratesonastraightlineab，whichshowsthatithasnothingwithrelativeroughness,buttherelationbetweenandfitsequationwhichisconsistentcompletelywiththelaminartheoryformulaofroundpipe.

(2)TransitionzoneThisareaisthetransitionareaoflaminarflowturningintoturbulentflow.Atthistimehasnothingwith,asshowninzone2oftheFigure6—12.§6–4FrictionalLossinPipeline

(3)TurbulentsmoothpipezoneAs,thoughflowkeepsturbulent,butexperimentalpointswithdifferentroughnessallconcentratesonlinecd，whichshowsthatroughnesshasnothingtodowithbutonlyhasrelationwithReynoldsnumber,thedepthoflaminarsub-layerisbiggerthanroughnessofpipe.§6–4FrictionalLossinPipeline

(4)TransitionzoneofturbulentflowWiththeincreaseofReynoldsnumberexperimentalpointsleavesfromlinecdaccordingtheroughnessofdifferentpoints