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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: cwklaw@ntu.edu.sg
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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

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