Double diffusive convection in the fingering regime is a commonly observed phenomenon in the (sub-)tropic ocean. It often happens when both temperature and salinity decrease with depth in the upper water
and plays a significant role in the vertical mixing and transport of heat and salt. In this study
we conduct two-dimensional direct numerical simulations of oceanic double diffusive convection in the fingering regime for four different combinations of component properties. We focus on the transport behaviors and flow structures
and their dependences on the control parameters
especially the influences of the Prandtl and Schmidt numbers. Results suggest that the overall trends of the dependences of heat and salt Nusselt numbers and Reynolds number on the Rayleigh number do not change for different density ratio
but their absolute values decrease as the density ratio becomes larger. This influence of density ratio becomes weaker as the Lewis number
i.e.
the ratio between the two diffusivities increases. The dependences can be described by power-law scalings. For most of cases
the dominant structures are slender salt fingers. For several cases with small Lewis number and large Rayleigh number
the dominant structures change to large rolls which is similar to the convection turbulence. The dependence of finger width on Rayleigh number matches the prediction of linear stability analysis. All these findings provide useful information for understanding oceanic double diffusive convection
and extending the experimental and numerical findings to real actual problems.
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references
YOU Y Z. A global ocean climatological atlas of the Turner angle: implications for double-diffusion and water-mass structure[J]. Deep Sea Research Part I: Oceanographic Research Papers, 2002, 49(11): 2075-2093.
TIMMERMANS M L, MARSHALL J. Understanding Arctic Ocean circulation: a review of ocean dynamics in a changing climate[J]. Journal of Geophysical Research: Oceans, 2020, 125(4): e2018JC014378. DOI:10.1029/2018jc014378
SCHMITT R W, LEDWELL J R, MONTGOMERY E T, et al. Enhanced diapycnal mixing by salt fingers in the thermocline of the tropical Atlantic[J]. Science, 2005, 308(5722): 685-688. DOI:10.1126/science.1108678
TIMMERMANS M L, TOOLE J, KRISHFIELD R, et al. Ice-Tethered Profiler observations of the double-diffusive staircase in the Canada Basin thermocline[J]. Journal of Geophysical Research Atmospheres, 2008, 113: C00A02. DOI:10.1029/2008jc004829
ROSEVEAR M G, GAYEN B, GALTON-FENZI B K. The role of double-diffusive convection in basal melting of Antarctic ice shelves[J]. PNAS, 2021, 118(6): e2007541118. DOI:10.1073/pnas.2007541118
STERN M E. The “salt-fountain” and thermohaline convection[J]. Tellus, 1960, 12(2): 172-175. DOI:10.3402/tellusa.v12i2.9378
KUNZE E. A review of oceanic salt-fingering theory[J]. Progress in Oceanography, 2003, 56(3-4): 399-417. DOI:10.1016/S0079-6611(03)00027-2
SCHMITT R W. Observational and laboratory insights into salt finger convection[J]. Progress in Oceanography, 2003, 56(3-4): 419-433. DOI:10.1016/S0079-6611(03)00033-8
YOSHIDA J, NAGASHIMA H. Numerical experiments on salt-finger convection[J]. Progress in Oceanography, 2003, 56(3-4): 435-459. DOI:10.1016/S0079-6611(03)00032-6
KRISHNAMURTI R. Double-diffusive transport in laboratory thermohaline staircases[J]. Journal of Fluid Mechanics, 2003, 483: 287-314. DOI:10.1017/s0022112003004166
FERNANDES A M, KRISHNAMURTI R. Salt finger fluxes in a laminar shear flow[J]. Journal of Fluid Mechanics, 2010, 658: 148-165. DOI:10.1017/s0022112010001588
HAGE E, TILGNER A. High Rayleigh number convection with double diffusive fingers[J]. Physics of Fluids, 2010, 22(7): 076603. DOI:10.1063/1.3464158
KELLNER M, TILGNER A. Transition to finger convection in double-diffusive convection[J]. Physics of Fluids, 2014, 26(9): 094103. DOI:10.1063/1.4895844
STELLMACH S, TRAXLER A, GARAUD P, et al. Dynamics of fingering convection. part 2 the formation of thermohaline staircases[J]. Journal of Fluid Mechanics, 2011, 677: 554-571. DOI:10.1017/jfm.2011.99
PAPARELLA F, VON HARDENBERG J. Clustering of salt fingers in double-diffusive convection leads to staircaselike stratification[J]. Physical Review Letters, 2012, 109: 014502. DOI:10.1103/physrevlett.109.014502
OSTILLA-MONICO R, YANG Y T, VAN DER POEL E P, et al. A multiple-resolution strategy for Direct Numerical Simulation of scalar turbulence[J]. Journal of Computational Physics, 2015, 301: 308-321. DOI:10.1016/j.jcp.2015.08.031
YANG Y T, VAN DER POEL E P, OSTILLA-MÓNICO R, et al. Salinity transfer in bounded double diffusive convection[J]. Journal of Fluid Mechanics, 2015, 768: 476-491. DOI:10.1017/jfm.2015.93
YANG Y T, VERZICCO R, LOHSE D. Scaling laws and flow structures of double diffusive convection in the finger regime[J]. Journal of Fluid Mechanics, 2016, 802: 667-689. DOI: 10.1017/jfm.2016.484
YANG Y T. Double diffusive convection in the finger regime for different Prandtl and Schmidt numbers[J]. Acta Mechanica Sinica, 2020, 36(4): 797-804. DOI:10.1007/s10409-020-00973-0
YANG Y, CHEN W, VERZICCO R, et al. Multiple states and transport properties of double-diffusive convection turbulence[J]. Proceedings of the National Academy of Sciences of the United States of America, 2020, 117(26): 14676-14681. DOI:10.1073/pnas.2005669117