Interaction of multiple jets and plumes

这项工作涉及组的射流或羽流在密切接近，以及它们的相互作用如何导致流结构，是从一个孤立的射流或羽流不同。将开展三个项目：（1）申请人以前的工作表明，湍流涡量传输（在横流中形成的射流或羽流中的对转涡之间）如何直接导致环流衰减，主要发生在中心平面上。该分析使用环流的流向空间导数和横流速度来近似环流衰减的时间速率。在拟议的研究中，将进行横流中湍流射流的直接数值模拟（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的研究表明，与单射流相比，直列射流的穿透力增强，而当它们并排时穿透力降低。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面喷嘴发出的射流/羽流的近场行为的差异相比，从堆栈，提供有关的最佳源配置的设计信息，以提高渗透和解释这些过程的近场效应。(3)在工程应用中，雷暴下击暴流（比加拿大的龙卷风更频繁）是用一个圆形的动量喷流撞击地面来模拟的。申请人与一位美国气象学家的合作为更真实的密度驱动下击暴流提供了计算流体动力学模型。拟议的研究将通过检查两个或多个事件的相互作用来扩展这个模型（因为这经常发生在雷暴中），并通过使用密集流体包释放到更大的水库中的实验来验证。这项工作将有助于评估多个下击暴流对长结构（如输电线路）的影响，并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.