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PIV based POD analysis of coherent structures in flow patterns generated by triple interacting buoyant plumes
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region.
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region; College of Civil Engineering and Architecture, Zhejiang University, Yuhangtang Road, Hangzhou, China .
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology.
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong Special Administrative Region.
2019 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 158, p. 165-181Article in journal (Refereed) Published
Abstract [en]

The paper performs an investigation on multi-scale coherent structures that exist in different flow patterns of triple interacting plumes. Time-averaged and turbulent flow characteristics are first obtained by the two-dimensional (2-D) particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) method is then applied to extract the dominant coherent structures. Energy contributions, POD modes, and POD coefficients are systematically explored to understand the spatial-temporal characteristics of the coherent structures. The first three POD modes are most important in the turbulent kinetic energy (TKE). Mode 1, as the most dominant mode, can contain about 10% TKE in an average sense. In addition, the first 12–14 POD modes can totally contribute 50% TKE. Hierarchical four-scale flow structures, independent of the flow patterns, are clearly identified when mode number increases, which are successively characterized by main flows (the 1st scale), larger-scale outer-side vortex rings (the 2nd scale), shear-layer vortex shedding (the 3rd scale), and smaller-scale homogeneous turbulent vortices (the 4th scale). Frequency spectra analysis confirms the co-existence of lower-frequency and higher-frequency periodic cycles in one certain POD mode. Dominant frequencies of the first three POD coefficient series (a1–a3) fall into the range of 0.025–0.187 Hz. Probability density analysis has identified negative/positive peak probability densities of the series a1. Cumulative probabilities of negative and positive coefficients are approximately equivalent during the sampling period. 

Place, publisher, year, edition, pages
2019. Vol. 158, p. 165-181
Keywords [en]
Coherent structure, Energy contribution, Flow pattern, POD coefficient, POD mode, Triple interacting plumes, Flow fields, Kinetic energy, Kinetics, Principal component analysis, Probability, Shear flow, Turbulent flow, Velocity measurement, Vortex flow, POD modes, Flow patterns, decomposition analysis, particle image velocimetry, plume, probability density function, sampling, spatiotemporal analysis, spectral analysis, vorticity
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:hig:diva-30534DOI: 10.1016/j.buildenv.2019.04.055ISI: 000468894500015Scopus ID: 2-s2.0-85065614068OAI: oai:DiVA.org:hig-30534DiVA, id: diva2:1344647
Available from: 2019-08-21 Created: 2019-08-21 Last updated: 2019-08-22Bibliographically approved

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Sandberg, Mats

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