%0 Journal Article %1 Wells1999 %A Wells, M. G. %A Griffiths, R. W. %A Turner, J. S. %D 1999 %J JOURNAL OF FLUID MECHANICS %K CONVECTION; CORE; EARTHS FLUID %P 319--336 %T Competition between distributed and localized buoyancy fluxes in a confined volume %V 391 %X We investigate the convection and density stratification that form when buoyancy fluxes are simultaneously applied to a finite volume in both a turbulent buoyant plume from a small source and as a uniform heat flux from a horizontal boundary. The turbulent plume tends to produce a stable density stratification, whereas the distributed flux from a boundary tends to force vigorous overturning and vertical mixing. Experiments show that steady, partially mixed and partially stratified states can exist when the plume buoyancy flux is greater than the distributed flux. When the two fluxes originate from the same boundary, the steady state involves a balance between the rate at which the mixed layer deepens due to encroachment and vertical advection of the stratified water far from the plume due to the plume volume flux acquired by entrainment. There is a monotonic relationship between the normalized mixed layer depth and flux ratio R (boundary flux/plume flux) for 0 < R < 1, and the whole tank overturns for R > 1. The stable density gradient in the stratified region is primarily due to the buoyancy from the plume but is strengthened by a stabilizing temperature gradient resulting from entrainment of heat into the plume from the mixed layer. This result may be relevant to the upper oceans of high latitude where there is commonly a destabilizing heat flux from the sea surface as well as more localized and intense deep convection from the surface. For the case of fluxes from a plume on one boundary and a uniform heat flux from the opposite boundary the shape of the density profile is that given by the Baines & Turner (1969) 'filling-box' mechanism, with the gradient reduced by a factor (1 + R) due to the heating. Thus, when R < -1 there is no stratified region and the whole water column overturns. When 0 > R > -1, the constant depth of the convecting layer is determined by a balance between buoyancy and turbulent kinetic energy in the outflow layer from the plume.

@article{Wells1999, abstract = {We investigate the convection and density stratification that form when buoyancy fluxes are simultaneously applied to a finite volume in both a turbulent buoyant plume from a small source and as a uniform heat flux from a horizontal boundary. The turbulent plume tends to produce a stable density stratification, whereas the distributed flux from a boundary tends to force vigorous overturning and vertical mixing. Experiments show that steady, partially mixed and partially stratified states can exist when the plume buoyancy flux is greater than the distributed flux. When the two fluxes originate from the same boundary, the steady state involves a balance between the rate at which the mixed layer deepens due to encroachment and vertical advection of the stratified water far from the plume due to the plume volume flux acquired by entrainment. There is a monotonic relationship between the normalized mixed layer depth and flux ratio R (boundary flux/plume flux) for 0 < R < 1, and the whole tank overturns for R > 1. The stable density gradient in the stratified region is primarily due to the buoyancy from the plume but is strengthened by a stabilizing temperature gradient resulting from entrainment of heat into the plume from the mixed layer. This result may be relevant to the upper oceans of high latitude where there is commonly a destabilizing heat flux from the sea surface as well as more localized and intense deep convection from the surface. For the case of fluxes from a plume on one boundary and a uniform heat flux from the opposite boundary the shape of the density profile is that given by the Baines & Turner (1969) 'filling-box' mechanism, with the gradient reduced by a factor (1 + R) due to the heating. Thus, when R < -1 there is no stratified region and the whole water column overturns. When 0 > R > -1, the constant depth of the convecting layer is determined by a balance between buoyancy and turbulent kinetic energy in the outflow layer from the plume.}, added-at = {2009-11-03T20:21:25.000+0100}, author = {Wells, M. G. and Griffiths, R. W. and Turner, J. S.}, biburl = {https://www.bibsonomy.org/bibtex/2c22750f1fadc2a1375bf7c611cecb72e/svance}, citedreferences = {ADRIAN RJ, 1986, EXP FLUIDS, V4, P121 ; BAINES WD, 1969, J FLUID MECH, V37, P51 ; BARNETT S, 1991, THESIS CAMBRIDGE U ; BLOOMFIELD LJ, 1998, J FLUID MECH, V358, P335 ; DEARDORFF JW, 1980, J FLUID MECH, V100, P41 ; DENTON RA, 1981, J FLUID MECH, V113, P1 ; FEARN DR, 1981, Nature, V289, P393 ; FEARN DR, 1981, Nature, V292, P232 ; KAYE GWC, 1973, TABLE PHYSICAL CHEM ; KILLWORTH PD, 1982, GEOPHYS ASTROPHYS FL, V20, P265 ; LEVITUS S, 1987, CLIMATOLOGICAL ATLAS ; LIDE DR, 1985, CRC HDB CHEM PHYSICS ; MANINS PC, 1977, Q J R MET SOC, V104, P39 ; MANINS PC, 1979, J FLUID MECH, V91, P765 ; MCDOUGALL TJ, 1983, J FLUID MECH, V133, P321 ; PIERCE DW, 1996, J PHYS OCEANOGR, V26, P176 ; RUDDICK BR, 1979, DEEP SEA RES A, V26, P775 ; TURNER JS, 1973, BUOYANCY EFFECTS FLU ; TURNER JS, 1986, J FLUID MECH, V173, P431 ; WHALER KA, 1980, Nature, V287, P528 ; WORSTER MG, 1983, J FLUID MECH, V132, P457}, interhash = {df6096fc996527f323782fdd03f3b961}, intrahash = {c22750f1fadc2a1375bf7c611cecb72e}, journal = {JOURNAL OF FLUID MECHANICS}, keywords = {CONVECTION; CORE; EARTHS FLUID}, owner = {svance}, pages = {319--336}, timestamp = {2009-11-03T20:22:20.000+0100}, title = {Competition between distributed and localized buoyancy fluxes in a confined volume}, volume = 391, year = 1999 }