Coaxial jets of different mean velocity ratios

Abstract

A detailed study of coaxial jets of mean velocity ratios (inner to outer) 0·15≤λ -1 ≤1 has been done. In this part of the study the mean and fluctuating properties within the outer and inner regions across the jet are presented. In the outer region good similarity of the profiles of mean velocity, turbulence intensity and pressure intensity is found. Agreement with the similarity of the profiles of single jet is also found. In the inner region only the similarity of the profiles of mean velocity ratios is found. The results for the fluctuating properties and flow visualization indicate the presence of two trains of structures in the outer and inner regions of the coaxial jets. In the outer region the outer structures, which are similar in characteristics as those of a single jet, are observed over the whole mean velocity ratios considered. For the structures inside the inner region their characteristics depend on the mean velocity ratio λ -1 . For λ -1 ≥0·8 the alternating vortices shed behind the inner nozzle lip are the only ones present. For λ -1 < 0·15 the inner structures, which exhibit characteristics similar to those of the outer structures, are dominant and have an opposite sense of direction to those of the outer structures. For 0·5 < λ -1 < 0·8 both the alternating vortices and the inner structures are present in the inner region and their respective dominance depends on mean velocity ratio. © 1985.