The use of duckbill valves in submerged outfalls for dense effluents is now prevalent to prevent the intrusion of ambient water into the outfall pipe during periods of low production of the facility. 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 a duckbill shape nozzle in co-flowing currents. The measured characteristics included the jet trajectory, concentration decay, centreline peak dilution and cross-sectional concentration distribution. The Froude number ranged from 10 to 25, and the nominal Froude number from 0.2 to 3.0. Two mounting orientations of the duckbill nozzle, namely vertical and horizontal, were also investigated. The experimental results showed that two regimes, namely dense-jet- and co-flow-dominated, can be clearly observed. When the co-flow velocity increases, the centreline peak height and dilution of the inclined dense jet decrease. Comparing to the available results in the literature for inclined circular dense jets, the centreline peak dilution for inclined duckbill dense jets is generally higher. In other words, the installation of the duckbill valve also contributes to the mixing of the dense effluent with surrounding ambient waters, in addition to preventing the ambient intrusion. With respect to the mounting orientation, the horizontal induces a relatively higher dilution but also a larger centreline peak height. Thus, the horizontal orientation would be preferable when the cover water depth is sufficient, while the vertical orientation can be considered in shallow waters for full submergence.

如今，在设施密集的污水淹没式排污口中普遍使用鸭嘴阀，以防止在设备产量较低时环境水进入排污管。在本研究中，使用平面激光诱导荧光（PLIF）技术进行了实验研究，以检验鸭嘴形喷嘴中45°倾斜致密射流在顺流中的混合特性。测得的特性包括射流轨迹，​​浓度衰减，中心线峰稀释度和横截面浓度分布。弗劳德数在10到25之间，标称弗劳德数在0.2到3.0之间。还研究了鸭嘴喷嘴的两个安装方向，即垂直和水平方向。实验结果表明，两种方案 可以清楚地观察到，即以密集射流和顺流为主。当同流速度增加时，中心线峰高和倾斜密集射流的稀释度会降低。与文献中倾斜的圆形密集喷射器的现有结果相比，倾斜的鸭嘴密集喷射器的中心线峰稀释度通常更高。换句话说，鸭嘴阀的安装除了有助于防止环境侵入之外，还有助于将浓的废水与周围的环境水混合。对于安装方向，水平方向会导致较高的稀释度，但中心线的峰值高度也会较大。因此，当盖水深度足够时，最好采用水平方向，而在浅水中完全浸没时可以考虑采用垂直方向。