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Dynamic interaction of multiple buoyant jets

Published online by Cambridge University Press:  10 August 2012

Adrian C. H. Lai  and
Joseph H. W. Lee
Adrian C. H. Lai
Affiliation:
The Center for Environmental Sensing and Modelling, Singapore–MIT Alliance for Research and Technology Centre, 1 CREATE Way, CREATE Tower, Singapore 138602, Republic of Singapore
Joseph H. W. Lee*
Affiliation:
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, People’s Republic of China
*
†Email address for correspondence: jhwlee@ust.hk
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Abstract

An array of closely spaced round buoyant jets interact dynamically due to the pressure field induced by jet entrainment. Mutual jet attraction can result in a significant change in jet trajectories. Jet merging also leads to overlapping of the passive scalar fields associated with the individual jets, resulting in mixing characteristics that are drastically different from those of an independent free jet. A general semi-analytical model for the dynamic interaction of multiple buoyant jets in stagnant ambient conditions is proposed. The external irrotational flow field induced by the buoyant jets is computed by a distribution of point sinks with strength equal to the entrainment per unit length along the unknown jet trajectories and accounting for boundary effects. The buoyant jet trajectories are then determined by an iterative solution of an integral buoyant jet model by tracking the changes in the external entrainment flow and dynamic pressure fields. The velocity and concentration fields of the jet group are obtained by momentum or kinetic energy superposition for merged jets and plumes, respectively. The modelling approach is supported by numerical solution of the Reynolds-averaged Navier–Stokes equations. The model shows that jet merging and mixing can be significantly affected by jet interactions. Model predictions of the multiple jet trajectories, merging height, as well as the centreline velocity and concentration of the buoyant jet group are in good agreement with experimental data for: (i) a clustered momentum jet group; (ii) a turbulent plume pair; and (iii) a rosette buoyant jet group. Dynamic interactions between a jet group are shown to decrease with the addition of an ambient cross-flow.

JFM classification

Wakes/Jets: Jets Convection: Plumes/thermals Mixing: Turbulent mixing

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Type
Papers
Information
Journal of Fluid Mechanics , Volume 708 , 10 October 2012 , pp. 539 - 575
Copyright
Copyright © Cambridge University Press 2012

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