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Jet interaction in a still or co-flowing environment

Authors Wang, Haijing
Issue Date 2000
Summary The problem of jet interaction between a line of merging jets in a co-flowing ambient fluid is dealt with in the thesis. A comprehensive study is conducted into the interaction between the jet and its co-flowing ambient environment and between the jet and its neighboring discharges, with and without the presence of a co-flowing ambient current. Laser Induced Fluorescence (LIF) techniques are to study these flows. A modified form of LIF, the Profile Tracking System (PTS) is developed to make measurements at previously inaccessible dimensionless distances for a discharge in a moving environment. With the PTS, data could be gathered at dimensionless distances that are an order of magnitude greater than those previously obtained for the co-flowing jet problem, which enables the mean and fluctuating behavior of the flow in the strongly-advected region to be more clearly defined. Experimental results from a single axisymmetric jet in a co-flow, show that both the spread constant and the ratio of the tracer to the velocity spread change from the weakly to strongly advected region. However the mean concentration profiles remain Gaussian and self-similar during the transition from the weakly advected to strongly advected behavior. In addition the experiments provide information on the contrasts between the mixing processes in the weakly-advected and strongly-advected regions, and their influence on the mean behavior of these flows. Concentration fluctuation statistics from both regions are presented and implications for the application of the entrainment assumption in the strongly-advected region are also discussed. Interaction between a jet and its neighbors is initially dealt with in a still ambient fluid without the influence of ambient fluid. A model for the merging of an infinite line of equally spaced identical jets in a still ambient fluid is developed. The velocity and tracer distributions in the model are determined based on the summation of momentum fluxes and tracer fluxes respectively. Experiments are conducted for four different port spacings. The experimental results show that individual jet spreads asymmetrically once merging takes place and the current model satisfactorily predicts the spreading rate changes in the free entrainment plane and the jet containing plane, as well as the tracer distributions during the merging process. Flapping motions were observed during jet merging but seem not persistent enough to change the concentration fluctuations profiles. The study on interaction between jets with the existence of ambient co-flow exploits information obtained from the above investigations. Although the predictions from the new model generally agree with the experimental results, comparisons indicate that the spread of two-dimensional co-flowing jet is different from that of axisymmetric co-flowing jet, while the loss of self-similarity of concentration fluctuations are mainly due to the impact of the ambient co-flow.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2000
Language English
Format Thesis
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