Experimental Investigation Of Elliptical Jet In Coflow

Elliptic jet is an intermediate configuration between the two simple, and extensively, asymptotic geometries circular and plane jets, although the existence of two geometrical length scales (major and minor axis) make it more complicated. A detail study of elliptic jets facilitates a better understanding of the wider class of jets were the curvature of the coherent structure changes around the perimeter. The elliptical jet mixing has important implications in the design of combustors and the design of propulsion system. In addition elliptic jets have been used extensively as a means of rapid dilution of a concentrate fluid discharge into the environment.The present investigation is to study the mixing characteristics of elliptical jet at different jet aspect ratio in coflow ambient. A systematic three-dimensional numerical study using k-ε model and laboratory measurements by Laser induced Fluorescence (LJF) on a elliptical jet with varying large aspect ratios in coflow is presented.Laser induced Fluorescence techniques have been successfully developed to visualize and quantify the cross- sectional scalar concentration field. This technique has been applied to the study of centerline dilution of elliptical coflowing jet. This technique used to quantify the mean and turbulence characteristics of concentration fields of turbulent elliptical jets in ambient coflow. The cross-sectional scalar concentration fields, Centerline dilution and the characteristic jet width along the jet axis are also acquired. Experiments with a round jet in a coflowing ambient are studied as a control and to establish the accuracy of the LIF techniques. Compared to the circular jet, the jet issuing out of the nozzle is an elliptical jet with a medium and high aspect ratios (AR=3, 6 and 10).Our results indicate these high aspect ratio jets appear to introduce a much higher degree of dilution as compared to the coflowing circular jets. The experiments also revealed that the elliptical jet induce significantly an interesting axis switching in that the orientation of its minor axis is switched with the downstream distances. Beyond the jet axis switching, its cross-section gradually develops from an elliptical shape to a rounded one.The mean and turbulence characteristics of concentration fields at different velocity ratios in a coflowing ambient are investigated thoroughly. The concentration distribution in the major axis and minor axis planes can be well approximated by a Gaussian distribution for x/D≥1. Most previous studies focused on the experimental work to scrutinize the mixing behavior of jets. A major objective of this investigation is to provide a numerical simulation to facilitate the study of the elbptical jet in ambient flow instead of returning back to the experimental study, which is more complex and at the same time is a hard work. A comparison between the numerical predictions and the laboratory results is presented. The analysis indicates that the numerical results are well supported by the experimental data. Further more, the concentration to velocity width (λ= bgc/bg ) is obtained from the concentration and velocity profiles. λ is found to be equal to 1.18.