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

Abstract

In this study, the steady, incompressible and axis symmetric flows in the pipe entrance region has been simulated numerically for the Reynolds numbers between 1000 and 25000 and for the square edged pipe inlets. The developing boundary layer at the pipe entrance region first grows as laminer then disturbed to a turbulent state at downstream away of the inlet. From pipe inlet to a downstream distance where laminer to turbulent transition begins is called the transition length. Determination of the transition length has been significiant for hydro and aeromechanics and yet it seems not to be defined clearly. The effects of wall surface roughness, pipe diameter and Reynolds numbers on transition length has been investigated numerically by covering transition and turbulent flow regimes too. On the purpose, water flows were simulated numerically including five different relative roughness. The numerical results obtained has shown that the transiton length is the power function of the Reynolds number inverse proportionally. Likewise the numerical study has also shown that changing the pipe diameter but keeping the relative roughness the same has left no effect on the transition length. As an outcome, a numerical correlation which define the dimensionless transition length and well fitting the numerical values was derived as a function of Reynolds number.

Keywords

• Entrance length,Pipe flow,Developing flow,Numerical

References

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