Turbulent properties of a low Reynolds number, axisymmetric, pipe jet

Abstract

This paper presents the mean and turbulent properties of a low Reynolds number round jet (Re 5500), with a fully turbulent pipe flow initial velocity profile, from nozzle exit to the establishment of self similarity. Experimental data acquired with a 2-D Laser Doppler Anemometry system include jet flow parameters and velocity statistics, such as spreading, entrainment, axial and radial distributions of the axial velocity and higher order moments. A “preserving core” region is identified, in analogy to the potential core region observed in jets with a uniform central initial profile. A transition region is following and thereafter, self similarity is approached in steps with the mean axial velocity attaining first self similar profiles, while the axial fluctuations, the radial fluctuations and the turbulent Reynolds stresses follow. The form of all the measured self similar profiles compares well to previous findings, although the values of the turbulent properties are always lower compared to those of contraction round jets of significantly higher Reynolds number. The triple velocity products and skewness and flatness factors indicate a different eddy structure of the present jet compared to that of earlier reported contraction jets.