Motion of Dense Thermals on Incline
Publication: Journal of Hydraulic Engineering
Volume 117, Issue 12
Abstract
In this paper, results on the motion of two‐dimensional dense thermals descending on slopes of less than 5° are presented. The front propagation, concentration distribution, and internal structure of the thermals are investigated experimentally and analytically. Laboratory experiments are carried out in a 20‐m‐long water tank to determine the front velocity and the temperature field in cold, saline thermals. The similarity assumption is employed in the analysis of the results. The front velocities of the thermals agree well with analytical results, and the influence of the water depth at the source on the rate of advance of the front is insignificant. The similarity concept is shown to result in contradictions when applied to depth‐averaged parameters in the tail of the thermals. The internal structure of thermals is further examined by using laser‐induced fluorescence (LIP) flow visualization in a 1‐m‐long aquarium. The photographs show that three‐dimensional structures form at the front and engulf ambient fluid. The frontal part has oscillatory propagation of lobes and the ensuing development of large billows.
Get full access to this article
View all available purchase options and get full access to this article.
References
1.
Batchelor, G. K. (1954). “Heat convection and buoyancy effects in fluids.” Q. J. Royal Meteorological Soc., 80, 339–358.
2.
Beghin, P., Hopfinger, E. J., and Britter, R. E. (1981). “Gravitational convection from instantaneous sources on inclined boundaries.” J. Fluid Mech., 107, 407–422.
3.
Buehler, J., and Siegenthaler, C. (1986). “Self‐preserving solutions for turbidity currents.” Acta Mech., 63, 217–233.
4.
Bühler, J. (1980). “Density currents generated by submarine slumps.” Proc. 2nd Int. Symp. on Stratified Flows, The Norwegian Institute of Technology, Trondheim, Norway, 2, 636–646.
5.
Droegemeier, K. K., and Wilhelmson, R. B. (1985). “Kelvin‐Helmholtz instability in a numerically simulated thunderstorm outflow.” 14th Conf. Severe Local Storms, American Meteorological Society, 151–154.
6.
Ellison, T. H., and Turner, J. S. (1959). “Turbulent entrainment in stratified flows.” J. Fluid Mech., 6, 423–448.
7.
Escudier, M. P., and Maxworthy, T. (1973). “On the motion of turbulent thermals.” J. Fluid Mech., 61(3), 541–552.
8.
Keulegen, G. H. (1957). “An experimental study of the motion of saline water from locks into fresh water channels.” Nat. Bureau of Standards Report 5168, Nat. Bureau of Standards, Washington, D.C.
9.
Keulegen, G. H. (1958). “The motion of saline fronts in still water.” Nat. Bureau of Standards Report 5831, Nat. Bureau of Standards, Washington, D.C.
10.
Laval, A., Cremer, M., Beghin, P., and Ravenne, C. (1988). “Density surges: Two‐dimensional experiments.” Sedimentology, 35, 73–84.
11.
Lin, S. C., Tsang, L., and Wang, P. C. (1972). “Temperature field structure in strongly heated buoyant thermals.” Phys. Fluids, 15(12), 2118–2128.
12.
Morton, B. R., Taylor, G. I., and Turner, J. S. (1956). “Turbulent gravitational convection from maintained and instantaneous sources.” Proc. Roy. Soc. A 234, 1–23.
13.
Richards, J. M. (1961). “Experiments on the penetration of an interface by buoyant thermals.” J. Fluid Mech., 11, 369–384.
14.
Richards, J. M. (1963). “Experiments on the motions of isolated cylindrical thermals through unstratified surroundings.” Int. J. Air Water Pollut., 7, 17–34.
15.
Rottman, J. W., and Simpson, J. E. (1983). “Gravity currents produced by instantaneous releases of a heavy fluid in a rectangular channel.” J. Fluid Mech., 135, 95–110.
16.
Schläpfer, D. B. (1990). “Stationäre zwei‐dimensionale Dichteströmungen bei kleinen Neigungen. Einfluss der Reibung und den Tiefe.” Bericht Nr. R28‐90 Institut für Hydromechanik u. Wasserwirtschaft, ETH Zürich, Zürich, Switzerland.
17.
Scorer, R. S. (1957). “Experiments on convection of isolated masses of buoyant fluid.” J. Fluid Mech., 2, 583–594.
18.
Simpson, J. E. (1987). Gravity currents in the environment and the laboratory. John Wiley and Sons, New York, N.Y.
19.
Simpson, J. E., and Britter, R. E. (1979). “The dynamics of the head of a gravity current advancing over a horizontal surface.” J. Fluid Mech., 94, 477–485.
20.
Turner, J. S. (1973). Buoyancy effects in fluids. Cambridge Univ. Press, London, England.
21.
Wang, C. P. (1971). “Motion of an isolated buoyant thermal.” Phys. Fluids, 14(8), 1643–1647.
22.
Wang, C. P. (1973). “Motion of a turbulent buoyant thermal in a calm stably stratified atmosphere.” Phys. Fluids, 14(8), 744–749.
23.
Woodward, B. (1959). “The motion in and around isolated thermals.” Q. J. Royal Meteorological Soc., 85, 144–151.
Information & Authors
Information
Published In
Copyright
Copyright © 1991 ASCE.
History
Published online: Dec 1, 1991
Published in print: Dec 1991
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.