In the present study, we performed a laboratory investigation to examine the mixing characteristics of 45° inclined dense jets from different nozzle geometries using the technique of Planar Laser Induced Fluorescence (PLIF). The geometries included the circular, square and diamond shapes, as well as the duckbill shape of non-return duckbill valves that are now commonly used for brine outfalls and the star shape of non-return star valves that are available commercially but have not been adopted so far. The concentration centrelines, cross-sectional profiles and spread widths were quantified in the experiments. The results showed that 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. Interestingly, the duckbill nozzle has a relatively lower rise height compared to the others, potentially due to the strong influence of axis-switching effect. In addition, we also performed numerical simulations using the Large Eddy Simulations (LES) approach with the Dynamic Smagorinsky sub-grid model for the diamond, duckbill and star shape nozzle geometries in the experiments. The comparison showed that the time-averaged geometrical characteristics from the three different nozzle geometries can be simulated reasonably well before the centreline peak but with slight over-predictions after that. Meanwhile, the dilution characteristics are underestimated by ~25% generally, which are similar to previous LES results with the reference circular nozzle. The spectral density distribution of the concentration fluctuations clearly demonstrated that the production of turbulence energy in the larger eddies is enhanced by the non-circular nozzles, which is also consistent with the increase in dilutions with these nozzles.

在本研究中，我们进行了实验室研究，以使用平面激光诱导荧光（PLIF）技术检查来自不同喷嘴几何形状的45°倾斜致密喷嘴的混合特性。几何形状包括圆形，正方形和菱形，以及现在通常用于盐水排泄口的止回鸭嘴阀的鸭嘴形状，以及市售但尚未采用的止回星阀的星形。至今。在实验中量化浓度中心线，横截面轮廓和铺展宽度。结果表明，圆形，方形和菱形喷嘴的几何形状具有相似的行为，这表明它们的排放长度尺度的差异不足以引起明显的影响。另一方面，鸭嘴形和星形喷嘴的几何形状在中心线的峰值和返回点都具有相对较高的稀释度。有趣的是，鸭嘴喷嘴的上升高度相对于其他喷嘴而言较低，这可能是由于轴切换效果的强烈影响。此外，我们还在实验中使用大涡模拟（LES）方法和动态Smagorinsky子网格模型对金刚石，鸭嘴形和星形喷嘴几何图形进行了数值模拟。比较结果表明，可以很好地模拟来自三种不同喷嘴几何形状的时间平均几何特征，而在中心线峰值之前就可以很好地模拟它，但是在此之后会有一点过高的预测。同时，稀释特性通常被低估约25％，与先前的参考圆形喷嘴的LES结果相似。浓度波动的光谱密度分布清楚地表明，非圆形喷嘴可增强较大涡流中湍流能量的产生，这也与这些喷嘴稀释液的增加相一致。