Experimental study of confined coaxial jets in a non-axisymmetric co-flow

I A Sofia Larsson,B Daniel Marjavaara,T Staffan Lundström,Henrik Lycksam

doi:10.1007/s00348-020-03094-3

I A Sofia Larsson, B Daniel Marjavaara + Show 2 more

Open Access

https://doi.org/10.1007/s00348-020-03094-3

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Abstract

Confined, turbulent, coaxial jets in a non-axisymmetric co-flow are studied using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) simultaneously. Eight different cases are measured. Two momentum flow ratios of the co-flow are used in the experiment to investigate the effect on the coaxial burner jet behavior and mixing characteristics of the coaxial jet flow and the co-flowing, secondary fluid. In addition, four different momentum flow ratios of the coaxial outer to inner jet are investigated. The objective of the study is to get a deeper understanding of how the flow dynamics affects the entrainment and mixing process in a coaxial jet with a non-axisymmetric, surrounding co-flow. The results show that the introduction of a coaxial stream affects the inner jet and decreases the mixing with the surrounding co-flow; the effect is enhanced as the momentum flow ratio of the coaxial jet increases. The distribution of the secondary, co-flowing fluid controls the shape and direction of the coaxial jet, but does not have a significant impact on the mixing process near the centerline. Practical implications of this investigation are related to the possibility to better control a diffusion flame by introducing a coaxial stream. In this context it is concluded that it is possible to affect the jet development and hence the flame length. The conclusion is based on the assumption that the outer, coaxial stream has a low mass flow, not enough to provide complete combustion, and hence the co-flowing, secondary fluid provides the air needed for the combustion process.Graphic abstract

Highlights

Coaxial jets consist of an inner jet with a surrounding coaxial flow, issued into a still or co-flowing environment
The flow characteristics directly affect the mixing rate which is the slowest step of the combustion process affecting the efficiency of the combustion
The objective of the study is to get a deeper understanding of how the flow dynamics affects the entrainment and mixing process in a coaxial jet with a non-axisymmetric surrounding co-flow

Summary

Introduction

Coaxial jets consist of an inner jet with a surrounding coaxial flow, issued into a still or co-flowing environment. Their mixing capabilities make them important in many different applications, including burners and, especially, diffusion flames where the fuel and air enter separately as turbulent jets. This means that the necessary combustion air needs to be entrained and mixed with the fuel. By studying turbulent, coaxial jets, important predictions regarding flame characteristics and the effect of different flow parameters on the combustion process can be made (Lotfiani et al 2013)

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