Interaction of multiple jets and plumes

这项工作涉及近距离的喷流或羽流群，以及它们的相互作用如何导致不同于孤立的喷流或羽流的流动结构。将开展三个项目：(1)申请人以前的工作表明，湍流涡量输送(在横流中形成的相反旋涡之间)如何直接导致环流衰减，主要发生在中心平面上。该分析使用环流的空间导数和横流速度来近似估计环流衰减的时间速率。在拟议的研究中，将对横流中的湍流射流进行直接数值模拟，直接评估环流的时间变化率，从而对先前建立的模型进行验证和扩展。(2)申请人之前对从地面圆形喷嘴发射的单喷流和双喷流的研究表明，与单喷流相比，串联喷流的侵彻增强，而并行喷流的侵彻减少。其他关于烟囱发出的浮力羽流的研究，并没有显示出完全相同的趋势。拟议的研究将审查从地面喷嘴喷出的射流/羽流的近场行为与从烟囱喷出的喷流/羽流近场行为的差异，提供关于增强渗透的最佳源配置的设计信息，并解释近场对这些过程的影响。(3)对于工程应用，雷暴下暴流(在加拿大比龙卷风更频繁)是用撞击地面的圆形动量急流模拟的。申请者与一位美国气象学家的合作为更现实的、密度驱动的下击暴流提供了CFD模型。拟议的研究将通过检查两个或更多近距离事件的相互作用(因为这通常发生在雷暴中)来扩展这一模型，并通过将稠密的流体包释放到更大的水库中的实验来提供验证。这项工作将用于评估多个下击暴流对长结构(如输电线路)的影响，并将有助于开发此类事件的风险模型。

The work concerns groups of jets or plumes in close proximity and how their interaction results in flow structures that are different from an isolated jet or plume. Three projects will be undertaken: (1) Previous work by the applicant has shown how turbulent vorticity transport (between the contrarotating vortices that form in a jet or plume in a crossflow) directly results in the decay of circulation, mostly occurring on the centre plane. That analysis approximated temporal rates of circulation decay using the streamwise spatial derivative of circulation and the crossflow velocity. In the proposed research a direct numerical simulation (DNS) of a turbulent jet in a crossflow will be carried out, giving direct assessment of temporal rates of change of circulation, thereby providing validation and extension of the previously established model. (2) Previous studies by the applicant on single and twin jets, issuing from ground plane circular nozzles, show that penetration is enhanced for in-line jets and reduced when they are side-by-side, when compared to a single jet. Other work, on buoyant plumes issuing from stacks, does not show exactly the same trends. The proposed research will examine the differences in near field behaviour of jets/plumes issuing from ground plane nozzles compared to those from stacks, providing design information concerning the optimum source configurations for enhancing penetration and an explanation of the near-field effects on those processes. (3) For engineering applications thunderstorm downbursts (more frequent than tornados in Canada) are modelled using a circular momentum jet that impinges upon a ground plane. The applicant's collaboration with a US meteorologist has preovided a CFD model for a more realistic, density driven, downburst. The proposed research will extend this model by examining the interaction of two or more events in close proximity (since this often occurs in thunderstorms), with validation provided by experiments using the release of dense fluid packets into a larger reservoir. The work will be of use in assessing the effects of multiple downbursts on long structures, such as transmission lines, and will also aid the development of risk models for such events.