Developing Turbulent Flow in Pipes and Analysis of Entrance Region

Abstract

Turbulent flows have complex structures due to its nature and its’ analyses are hard either by numerical or experimental means. Hydrodynamic development of turbulent flow is also complex. In this study, velocity distribution in hydrodynamic entrance length of pipes is investigated depending on axial and radial locations. Literature was surveyed for a single empirical expression that provides velocity profile directly according to Reynolds number, radial and axial locations. Requisite for computational fluid dynamics in hydrodynamic entry length of pipes is stressed by assessing turbulence magnitudes in radial and axial directions. Evaluation of the region and its properties are conducted from heat transfer perspective. An axisymmetric pipe entrance region was analyzed by means of a commercial CFD code with nondimensional parameters. Four different Reynolds numbers that are 5x103, 1x104, 5x104, 1x105 were used in calculations. k-ϵ turbulence model and standard wall functions were used for turbulence modeling. Hydrodynamic entry length, velocity profiles and turbulence indicator parameters results are presented by means of axial and radial profiles. According to the obtained results, radial velocity component values exist that would lead to radial thermal convection in hydrodynamic entrance length. It is found that simultaneous development of velocity profiles and turbulence quantities leads to characteristic velocity profiles. Also, it is seen that a good resolution in hydrodynamic entrance length can be easily achieved by computational fluid dynamics.