Near field characteristics of buoyant helium plumes

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• 作者：KUCHIMANCHI K BHARADWAJ ; DEBOPAM DAS ; PAVAN K SHARMA
• 关键词：Helium plume ; puffing ; PIV ; PLIF ; entrainment.
• 刊名：Sadhana
• 出版年：2015
• 出版时间：May 2015
• 年：2015
• 卷：40
• 期：3
• 页码：757-768
• 全文大小：1,832 KB
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• 作者单位：KUCHIMANCHI K BHARADWAJ (1)
  DEBOPAM DAS (1)
  PAVAN K SHARMA (2)
  
  1. Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, India
  2. Reactor Safety Division, Bhabha Atomic Research Center, Mumbai, 400085, India
  
• 刊物类别：Engineering
• 刊物主题：Engineering, general
  
• 出版者：Springer India, in co-publication with Indian Academy of Sciences
• ISSN：0973-7677

文摘

Puffing and entrainment characteristics of helium plumes emanating out into ambient air from a circular orifice are investigated in the present study. Velocity and density fields are measured across a diametric plane using Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) respectively in phase resolved manner. Experiments are performed in Froude numbers range 0.2-.4 and for Reynolds numbers 58-48. Puffing frequency measurements reveal that the plume puffing frequencies are insensitive to the plume exit conditions, since the instability is buoyancy driven. The frequencies obtained in the present case are in agreement with frequencies obtained by Cetegen & Kasper (1996) for plumes originating from circular nozzles of various L/D ratios. Velocity and density measurements reveal that toroidal vortex formed during a puffing cycle entrains ambient air as it traverses downstream and this periodic engulfment governs the entrainment mechanism in pulsating plumes. The obtained velocity and density fields are used to calculate mass entrainment rates. It is revealed that though the flow is unsteady, the contribution of unsteady term in mass conservation to entrainment is negligible, and it becomes zero over a puff cycle. Finally, an empirical relation for variation of mass entrainment with height has been proposed, in which the non-dimensional mass entrainment is found to follow a power law with the non-dimensional height.