Author(s): Dongdong Shao; Dingyong Huang; Baoxin Jiang; Adrian Wing-Keung Law
Keywords: Horizontal dense jets; Laminar regime; Transitional regime; Buoyancy induced instability; Concentration decay
Abstract: In a companion study, the authors explored the structure and stability, i.e., the tendency to bifurcate, of horizontal dense jets at low and moderate Reynolds numbers in the laboratory, and identified three different flow patterns characterised with distinctive structures from longitudinal and cross-sectional images, namely, primary jet with vertical secondary plume, primary jet with pseudo secondary jet, and quasi-turbulent horizontal buoyant jet, together with their distribution on the Re-Fr map. In this study, Planar Laser Induced Fluorescence (PLIF) was used for quantitative concentration measurement to further study jet mixing characteristics in this regime. The decay of the maximum concentration along the jet centerline, the cross-sectional concentration distribution at different downstream locations, as well as the jet spreading were examined using the processed PLIF data. The impact of the instability on the jet mixing and spreading characteristics, e.g., Re- and Fr- dependence of the concentration decay and spreading coefficients, were further analyzed. The results have implications to marine outfall system with reduced discharge flow rate, due to energy conservation or operational variability.