On the effect of a co-flowing stream on the structure of an axisymmetric turbulent jet

The aim of this paper is to study experimentally the turbulent structure of an axisymmetric jet submerged in the co-flowing stream of the test section of a wind tunnel. The experiments have been performed without and with three different velocities for the outer stream. The measurements were carried out by using Pitot tube and Stationary Hot-Wires. The influence of the outer stream and the confinement effect on the development of the turbulent jet are analyzed. It is shown that the streamwise variation of the excess mean velocity, the jet expansion and the spanwise distribution of the longitudinal normal Reynolds stress are close to that observed on free jets by other research groups. Self-similarity is also investigated. An extensive spectral analysis has also been done, and the centerline variations of the integral time scales and Taylor microscales are also presented. Only the third-order moment of the longitudinal velocity fluctuation exhibits a radial distribution very different from that expected in free jets. In the case of no outer stream, it is shown that the confinement effects dominate and modify significantly the jet structure. (C) 1998 Elsevier Science Inc. All rights reserved.