Interaction of multiple jets and plumes

这项工作关注的是近距离的喷流或羽流群，以及它们之间的相互作用如何导致与孤立的喷流或羽流不同的流动结构。(1)申请人以前的工作表明，湍流涡量输送（在急流或横流羽流中形成的对旋涡之间）如何直接导致环流衰减，主要发生在中心平面上。该分析利用环流的顺流空间导数和横流速度来近似估算环流衰减的时间速率。在本研究中，将对横流中的湍流射流进行直接数值模拟（DNS），直接评估环流的时间变化率，从而验证和扩展先前建立的模型。(2)申请人先前对从地平面圆形喷嘴发出的单射流和双射流进行的研究表明，与单射流相比，直线射流的穿透能力增强，并排射流的穿透能力降低。其他关于从烟囱中喷出的浮力羽流的研究，并没有显示出完全相同的趋势。拟议的研究将检查从地平面喷嘴发出的射流/羽流与从烟囱发出的射流/羽流在近场行为上的差异，提供有关增强穿透的最佳源配置的设计信息，并解释这些过程的近场影响。(3)在工程应用方面，雷暴暴（比加拿大的龙卷风更频繁）是用撞击地平面的圆形动量射流来模拟的。申请人与美国气象学家的合作为更现实的、密度驱动的下爆提供了一个CFD模型。拟议的研究将通过检查两个或多个近距离事件的相互作用（因为这经常发生在雷暴中）来扩展该模型，并通过将致密流体包释放到更大的水库的实验提供验证。这项工作将用于评估多次下爆对长结构（如输电线路）的影响，也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.