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Unsteady large-scale flow patterns and dynamic vortex movement in near-field triple buoyant plumes
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
2018 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 142, p. 288-300Article in journal (Refereed) Published
Abstract [en]

Unsteady flow patterns of interacting buoyant plumes are important for buoyant ventilation and particularly influence pollutant and heat transports in indoor and outdoor environments. This study reveals fundamental large-scale flow patterns in triple building plumes, investigates vortex moving trends during the pattern transition processes, and explores possible mechanisms of pattern diversity by two-dimensional (2-D) Particle Image Velocimetry (PIV). Total five tests are studied, including three different heat strengths Q (180, 90, and 30 W) and three source layouts characterized by the ratios of source spacing S to source width W (0.2, 0.5, and 1.0). Streamline distributions and axial velocity profiles clearly reveal three fundamental global flow patterns: a right-slanting asymmetrical flow pattern, a left-slanting asymmetrical flow pattern, and an axisymmetric flow pattern. Correspondingly, it indicates four basic transition processes, i.e., right-to-center, left-to-center, center-to-right, and center-to-left transitions (“center” represents the axisymmetric pattern). A novel vortex tracking method, based on lambda-2 (λ2) criterion and principles of the PIV technique, is developed and successfully applied to qualitatively track the vortex moving trends during the transition processes. The regular vortex moving trends are found to be reasonably consistent with the global pattern transition trends. The flow pattern diversity is speculated to be mainly driven by unstable heat source wall flows and downstream swaying motions in this study. These critical unstable motions are considered to probably relate to unstable lateral entrainment and vortex interaction, particularly beside the central plume. Consistently, the regular vortex moving trends are usually observed in and around the central plume.

Place, publisher, year, edition, pages
Elsevier Ltd , 2018. Vol. 142, p. 288-300
Keywords [en]
Dynamic vortex movement, PIV measurement, Transition mechanism, Triple buoyant plumes, Unsteady flow patterns, Vortex tracking, Buoyancy, Unsteady flow, Velocity measurement, Vortex flow, Buoyant plume, Dynamic vortices, PIV measurements, Flow patterns
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:hig:diva-27515DOI: 10.1016/j.buildenv.2018.06.027ISI: 000445440600026Scopus ID: 2-s2.0-85048721494OAI: oai:DiVA.org:hig-27515DiVA, id: diva2:1230624
Note

This work is supported financially by a RGC CRF project (grant no: HKU9/CRF/12G ) of the Hong Kong SAR government.

Available from: 2018-07-04 Created: 2018-07-04 Last updated: 2018-11-23Bibliographically approved

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Sandberg, Mats

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