Three-dimensional flow structure in highly buoyant jet by scanning stereo PIV combined with POD analysis |
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| Affiliation: | 1. Graduate School of Science and Technology, Niigata University, 8050 Nino-cho, Ikarashi, Nishi-ku, Niigata 950-2181, Japan;2. Visualization Research Center, Niigata University, 8050 Nino-cho, Ikarashi, Nishi-ku, Niigata 950-2181, Japan;1. Laboratory for Aero & Hydrodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Leeghwaterstraat 21, 2628 CA Delft, The Netherlands;2. Shell Projects & Technology, Postbus 38000, 1030 BN Amsterdam, The Netherlands;1. Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, Canada;2. Department of Computer and Information Sciences, Temple University, Philadelphia, USA;1. Chair of Fluidmechanics, University of Duisburg-Essen, 47057 Duisburg, Germany;2. Head of Department “Liquid Flow”, Physikalisch-Technische Bundesanstalt PTB, 38116 Braunschweig, Germany;1. Graduate School of Science and Technology, Niigata University, Japan;2. Flow Visualization Research Center, Niigata University, Japan;1. Visualization Research Center, Niigata University, Niigata, Japan;2. Graduate School of Science and Technology, Niigata University, Niigata, Japan |
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| Abstract: | The flow characteristics and the structure of highly buoyant jet of low density fluid issuing into a stagnant surrounding of high density fluid is studied by scanning stereo PIV combined with proper orthogonal decomposition (POD) analysis. The experiment is carried out at Froude number of 0.3 and Reynolds number of 200, which satisfies the inflow condition due to the unstable density gradient near the nozzle exit. An increase in the maximum mean velocity occurs and the vertical velocity fluctuation is highly amplified near the nozzle exit, which suggests the influence of inflow due to the unstable density gradient. The POD analysis indicates that the vertical velocity fluctuation is the major source of fluctuating energy contributing to the development of the highly buoyant jet. The examination of the POD modes show that the longitudinal structure of the vertical velocity fluctuation is generated along the jet axis having the opposite sign of velocity fluctuation on both sides of the jet axis. The vertical scale of the POD mode decreases with increasing the mode number and results in the frequent appearance of cross-flow across the buoyant jet. The reconstruction flow from the POD modes indicates that the vortex structure is caused by the highly sheared layer between the upward and downward velocity and the inflow is induced by the vortex structure. The magnitude of the vortex structure seems to be weakened with an increase in the distance from the nozzle and the buoyant jet approaches to an asymptotic state in the further downstream. |
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| Keywords: | Highly buoyant jet Scanning stereo PIV Proper orthogonal decomposition Three-dimensional flow Inflow |
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