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Descent and spread of negatively buoyant thermals

Published online by Cambridge University Press:  07 September 2015

G. G. Rooney
G. G. Rooney*
Affiliation:
Met Office, FitzRoy Road, Exeter EX1 3PB, UK
*
†Email address for correspondence: [email protected]
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Abstract

Results are presented from a numerical and analytical study of negatively buoyant thermals. The numerical study consists of large-eddy simulations of thermal descent and spread. The thermals are initiated by a spherical perturbation in the homogeneous background potential temperature. Simulations covering various release heights, thermal radii and thermal buoyancies are carried out. The analysis involves matching similarity models of a thermal and an axisymmetric gravity current, hence describing the flow evolution in terms of the initial conditions and flow coefficients only. The simulations demonstrate that the flow transition through the impingement region is relatively smooth, the main flow adjustment being in the initial post-release phase of the thermal. Comparison of the simulations and the model enables determination of the coefficients, and validation of the similarity approach to predict the radial speed, reduced gravity and depth of the spreading flow on the ground. The predictions of reduced gravity and depth also depend on quantification of the increase in gravity-current volume due to entrainment, which is obtained from the simulations.

JFM classification

Geophysical and Geological Flows: Atmospheric flows Geophysical and Geological Flows: Gravity currents Convection: Plumes/thermals
Type
Papers
Information
Journal of Fluid Mechanics , Volume 780 , 10 October 2015 , pp. 457 - 479
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Copyright
© Crown Copyright. Published by Cambridge University Press 2015 

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References

Anabor, V., Rizza, U., Nascimento, E. L. & Degrazia, G. A. 2011 Large-eddy simulation of a microburst. Atmos. Chem. Phys. 11 (17), 9323–9331.Google Scholar
Brown, A. R., Derbyshire, S. H. & Mason, P. J. 1994 Large-eddy simulation of stable atmospheric boundary layers with a revised stochastic subgrid model. Q. J. R. Meteorol. Soc. 120 (520), 1485–1512.Google Scholar
Bryan, G. H. & Fritsch, J. M. 2002 A benchmark simulation for moist nonhydrostatic numerical models. Mon. Weath. Rev. 138, 2917–2928.2.0.CO;2>CrossRefGoogle Scholar
Devenish, B. J., Rooney, G. G. & Thomson, D. J. 2010 Large-eddy simulation of a buoyant plume in uniform and stably stratified environments. J. Fluid Mech. 652, 75–103.Google Scholar
Dotzek, N. & Friedrich, K. 2009 Downburst-producing thunderstorms in southern Germany: radar analysis and predictability. Atmos. Res. 93 (1–3), 457–473.Google Scholar
Fujita, T. T.1986. DFW microburst. NTIS PB 86-131638. The University of Chicago, Chicago, USA.Google Scholar
Giangrande, S. E., Collis, S., Straka, J., Protat, A., Williams, C. & Krueger, S. 2013 A summary of convective-core vertical velocity properties using ARM UHF wind profilers in Oklahoma. J. Appl. Meteorol. Climatol. 52, 2278–2295.Google Scholar
Grandpeix, J.-Y. & Lafore, J.-P. 2010 A density current parameterization coupled with Emanuel’s convection scheme. part I: the models. J. Atmos. Sci. 67, 881–897.Google Scholar
Gray, M. E. B., Petch, J. C., Derbyshire, S. H., Brown, A. R., Lock, A. P., Swann, H. A. & Brown, P. R. A.2001. Version. 2.3 of the Met Office Large-Eddy Model: Part II. Scientific documentation. APR Turbulence and Diffusion Note 276. Met Office, Exeter, UK.Google Scholar
Grundy, R. E. & Rottman, J. W. 1986 Self-similar solutions of the shallow-water equations representing gravity currents with variable inflow. J. Fluid Mech. 169, 337–351.Google Scholar
Hallworth, M. A., Huppert, H. E., Phillips, J. C., Sparks, R. & Stephen, J. 1996 Entrainment into two-dimensional and axisymmetric turbulent gravity currents. J. Fluid Mech. 308, 289–311.Google Scholar
Khairoutdinov, M. & Randall, D. 2006 High-resolution simulation of shallow-to-deep convection transition over land. J. Atmos. Sci. 63, 3421–3436.CrossRefGoogle Scholar
Linden, P. F. 2012 Gravity currents – theory and laboratory experiments. In Buoyancy-Driven Flows (ed. Chassignet, E. P., Cenedese, C. & Verron, J.), pp. 13–51. Cambridge University Press.CrossRefGoogle Scholar
Lundgren, T. S., Yao, J. & Mansour, N. N. 1992 Microburst modelling and scaling. J. Fluid Mech. 239, 461–488.Google Scholar
Mason, P. J. 1989 Large-eddy simulation of the convective atmospheric boundary layer. J. Atmos. Sci. 46, 1492–1516.2.0.CO;2>CrossRefGoogle Scholar
Mason, P. J. 1994 Large-eddy simulation: a critical review of the technique. Q. J. R. Meteorol. Soc. 120 (515), 1–26.Google Scholar
May, P. T. & Rajopadhyaya, D. K. 1999 Vertical velocity characteristics of deep convection over Darwin, Australia. Mon. Weath. Rev. 127, 1056–1071.Google Scholar
Morton, B. R. 1997 Discrete dry convective entities: I Review. In The Physics and Parameterization of Moist Atmospheric Convection (ed. Smith, R. K.), NATO ASI Series, vol. 505, pp. 143–173. Springer.CrossRefGoogle Scholar
Mott, R. W. & Woods, A. W. 2011 Natural ventilation driven by periodic gusting of wind. J. Fluid Mech. 679, 58–76.Google Scholar
NATS2008 Low altitude windshear. Aeronautical Information Circular 84/2008. NATS Ltd, Hounslow, UK.Google Scholar
Patterson, M. D., Simpson, J. E., Dalziel, S. B. & van Heijst, G. J. F. 2006 Vortical motion in the head of an axisymmetric gravity current. Phys. Fluids 18 (4), 046601.Google Scholar
Rooney, G. G. & Linden, P. F. 2012 Radial jet due to plume impingement on a horizontal surface. Engng. Comput. Mech. 165, 223–233.Google Scholar
Rottman, J. W. & Simpson, J. E. 1983 Gravity currents produced by instantaneous releases of a heavy fluid in a rectangular channel. J. Fluid Mech. 135, 95–110.Google Scholar
Scorer, R. S. 1957 Experiments on convection of isolated masses of buoyant fluid. J. Fluid Mech. 2, 583–594.Google Scholar
Thomson, J. J. & Newall, H. F. 1885 On the formation of vortex rings by drops falling into liquids, and some allied phenomena. Proc. R. Soc. Lond. 39, 417–436.Google Scholar
Turner, J. S. 1973 Buoyancy Effects in Fluids. Cambridge University Press.CrossRefGoogle Scholar
Turner, J. S. 1986 Turbulent entrainment: the development of the entrainment assumption, and its application to geophysical flows. J. Fluid Mech. 173, 431–471.CrossRefGoogle Scholar
Walker, J. D. A., Smith, C. R., Cerra, A. W. & Doligalski, T. L. 1987 The impact of a vortex ring on a wall. J. Fluid Mech. 181, 99–140.Google Scholar

Rooney supplementary movie

A vertical section through the simulation domain for experiment L03

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Video 5.6 MB

Rooney supplementary movie

A vertical section through the simulation domain for experiment L03

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Video 6.9 MB

Rooney supplementary movie

A vertical section through the simulation domain for experiment L08

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Video 4.4 MB

Rooney supplementary movie

A vertical section through the simulation domain for experiment L08

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Video 5.7 MB

Rooney supplementary movie

A vertical section through the simulation domain for experiment L13

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Video 1.5 MB

Rooney supplementary movie

A vertical section through the simulation domain for experiment L13

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Video 2.8 MB