Mixing Characteristics of Inclined Dense Jets with Different Nozzle Geometries – An Experimental Study

In the present study, an experimental investigation was conducted using the technique of Planar Laser Induced Fluorescence (PLIF) to examine the mixing characteristics of 45° inclined dense jets from five different nozzle geometries. They included standard circular nozzles, square nozzles with rectangular and diamond layouts, non-return duckbill valves that are now commonly used for brine outfalls, and finally non-return star valves that are available commercially. The study aimed to quantify the near-field mixing behavior from the different nozzle geometries, including their trajectory profile, concentration decay along the trajectory, and cross-sectional concentration distribution. The experimental results suggested the circular, square and diamond nozzle geometries have similar behavior, implying that the differences of their discharge length scale are not sufficiently large to induce a significant effect. On the other hand, the duckbill and star nozzle geometries have relatively higher dilutions both at the centreline peak and return points, showing that they can be potentially superior for brine outfalls from the dilution viewpoint. Interestingly, the duckbill nozzle has a relatively lower rise height compared to the others due to the strong influence of axis-switching effect.