EFFECT OF DELAYED TRANSITION ON PIPE FLOW DISCHARGE-VELOCITY DYNAMICS

摘要

Velocity dynamics of flow discharging from a straight,smooth pipe undergoing delayed transition were investigated.Several lengths of pipe were utilized, yielding total flowdevelopment lengths of 65 to 550 pipe diameters, while theReynolds number was incrementally increased from 500 togreater than 15000. The extent of delayed transition was variedby introducing artificial tripping in the initial developmentstages of flow, with levels of tripping ranging from β = 0 to75% blockage in terms of the pipe’s cross-sectional area.Centerline velocity characteristics indicate strong instabilityphenomena accompanying the delayed transition process, whichare due to flow intermittency. Larger development lengths andweakly perturbed flow conditions (β = 10%) yield the strongestunsteadiness, with maximum turbulence intensity valuesexceeding two times their traditional maximum value associatedwith a transitional Reynolds number of about 2300.