Strongly Advected Jet in a Coflow

Abstract

We present the results of an experimental investigation into the behavior of a strongly advected jet (weak jet) in a coflowing ambient fluid. Laser-induced-fluorescence and image processing techniques are employed to provide quantitative information about the mean properties of the flow. Data are obtained at previously inaccessible distances from the flow source, enabling the mean and fluctuating behavior of the flow in the strongly advected region to be more clearly defined. The spread relationship, traditionally employed to model the mean behavior of these flows, is redefined based on this experimental information. Both the spread constant and the ratio of the tracer to the velocity spread are shown to change in the strongly advected region. The results presented are discussed in the context of recent observations about the importance of large-scale eddy motions in defining the mean behavior of weakly advected jets and plumes. In addition the experiments provide information on the contrasts between the mixing processes in the weakly advected and strongly advected coflowing jet regions, and their influence on the mean behavior of these flows. Concentration fluctuation statistics from both regions are presented and implications for the application of the entrainment assumption in the strongly advected region are also discussed.