Numerical Investigation of the Transition Length at the Entrance Region of Pipe Flows

Abstract

Inthis study, the steady, incompressible and axis symmetric flows in the pipeentrance region has been simulated numerically for the Reynolds numbers between1000 and 25000 and for the square edged pipe inlets. The developing boundarylayer at the pipe entrance region first grows as laminer then disturbed to aturbulent state at downstream away of the inlet. From pipe inlet to adownstream distance where laminer to turbulent transition begins is called thetransition length. Determination of the transition length has been significiantfor hydro and aeromechanics and yet it seems not to be defined clearly. Theeffects of wall surface roughness, pipe diameter and Reynolds numbers ontransition length has been investigated numerically by covering transition andturbulent flow regimes too. On the purpose, water flows were simulatednumerically including five different relative roughness. The numerical resultsobtained has shown that the transiton length is the power function of theReynolds number inverse proportionally. Likewise the numerical study has alsoshown that changing the pipe diameter but keeping the relative roughness thesame has left no effect on the transition length. As an outcome, a numericalcorrelation which define the dimensionless transition length and well fittingthe numerical values was derived as a function of Reynolds number.