Hostname: page-component-745bb68f8f-l4dxg Total loading time: 0 Render date: 2025-01-07T10:20:02.383Z Has data issue: false hasContentIssue false
  • English
  • Français

On the internal vorticity and density structures of miscible thermals

Published online by Cambridge University Press:  09 April 2013

B. Zhao ,
A. W. K. Law ,
A. C. H. Lai  and
E. E. Adams
B. Zhao
Affiliation:
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
A. W. K. Law*
Affiliation:
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore
A. C. H. Lai
Affiliation:
Center for Environmental Sensing and Modelling, Singapore–MIT Alliance for Research and Technology, 1 CREATE Way, 138602, Singapore
E. E. Adams
Affiliation:
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
*
†Email address for correspondence: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Miscible thermals are formed by instantaneously releasing a finite volume of buoyant fluid into stagnant ambient. Their subsequent motion is then driven by the buoyancy convection. The gross characteristics (e.g. overall size and velocity) of a thermal have been well studied and reported to be self-similar. However, there have been few studies concerning the internal structure. Here, turbulent miscible thermals (with initial density excess of 5 % and Reynolds number around 2100) have been investigated experimentally through a large number of realizations. The vorticity and density fields were quantified separately by particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques. Ensemble-averaged data of the transient development of the miscible thermals are presented. Major outcomes include: (i) validating Turner’s assumption of constant circulation within a buoyant vortex ring; (ii) measuring the vorticity and density distributions within the miscible thermal; (iii) quantifying the effect of baroclinicity on the generation and destruction of vorticity within the thermal; and (iv) identifying the significantly slower decay rate of the peak density as compared to the mean.

JFM classification

Convection: Convection Convection: Plumes/thermals
Type
Rapids
Information
Journal of Fluid Mechanics , Volume 722 , 10 May 2013 , R5
Copyright
©2013 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Batchelor, G. K. 1954 Heat convection and buoyancy effect in fluids. Q. J. R. Meteorol. Soc. 345, 339–358.CrossRefGoogle Scholar
Bond, D. & Johari, H. 2005 Effects of initial geometry on the development of thermals. Exp. Fluids 39 (3), 589–599.CrossRefGoogle Scholar
Bond, D. & Johari, H. 2010 Imapct of buoyancy on vortex ring development in the near field. Exp. Fluids 48 (5), 737–745.Google Scholar
Fischer, H. B., List, E. J., Koh, R. C. Y., Imberger, J. & Brooks, N. H. 1979 Mixing in Inland and Coastal Waters. Acedemic.Google Scholar
Hart, A. C. 2008 Interacting thermals. PhD thesis, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK.Google Scholar
Lundgren, T. S., Yao, J. & Mansour, N. N. 1992 Microburst modelling and scaling. J. Fluid Mech. 239, 461–488.Google Scholar
Otsu, N. 1979 Threshold selection method from gray-level histograms. IEEE Trans. Syst. Man. Cybern. 9 (1), 62–66.CrossRefGoogle Scholar
Richards, J. M. 1961 Experiments on the penetration of an interface by buoyant thermals. J. Fluid Mech. 11 (3), 369–384.CrossRefGoogle Scholar
Scorer, R. S. 1957 Experiments on convection of isolated masses of buoyant fluid. J. Fluid Mech. 2 (6), 583–594.Google Scholar
Thompson, R. S. & Snyder, W. H. 2000 Laboratory simulation of the rise of buoyant thermals created by open detonation. J. Fluid Mech. 417, 127–156.CrossRefGoogle Scholar
Turner, J. S. 1957 Buoyang vortex rings. Proc. R. Soc. Lond. A 239 (1216), 61–75.Google Scholar
Turner, J. S. 1972 On the energy deficiency in self-preserving convective flows. J. Fluid Mech. 53 (2), 217–226.CrossRefGoogle Scholar
Turner, J. S. 1973 Buoyancy Effects in Fluids. Cambridge University Press.CrossRefGoogle Scholar
Whittaker, R. J. & Lister, J. R. 2008 The self-similar rise of a buoyant thermal in very viscous flow. J. Fluid Mech. 606, 295–324.CrossRefGoogle Scholar
Zhao, B., Law, A. W. K., Adams, E. E., Shao, D. & Huang, Z. 2012 Effect of air release height on the formation of sediment thermal in water. J. Hydraul Res. 50 (5), 532–540.Google Scholar