Flow Development of Multi-Annular Jets in a Confinement: Effect of Expansion Ratio

Abstract

Confined coaxial jets have been widely used in gas turbine combustors, where the requirement is to achieve better mixing between two streams - fuel and air - prior to ignition so as to provide stable and complete combustion. Two shear layers, one between the central jet and the annular jet and other between the annular jet and the stagnant fluid outside the annular jet help in the mixing process for confined coaxial jets. Therefore, for improved mixing, a configuration of one central jet and two co-annular jets, called multi-annular or multicoaxial jets, has been considered. To understand mixing of these streams in a confinement (mixing chamber), the mean axial velocity profiles at different axial locations of the mixing chamber and the static pressure along the wall of the mixing chamber are measured for expansion ratio of 1 and 1.3. These quantities are also computed using CFD software, FLUENT, with Standard k-ε turbulence model. After validation of the CFD code, parametric studies have been carried out for different expansion ratios. The results provide a good understanding of the mixing process and flow development in expanding confinement.