Interaction of multiple jets and plumes

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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.