Heat, salt and momentum transport in a laboratory thermohaline staircase. (English) Zbl 1183.76029

Summary: Flow characteristics and fluxes in thermohaline staircases are measured in two tanks differing in aspect ratio A, where A is the ratio of tank width to fluid depth. In one tank (the ‘\(1 \times 1\)’ tank) which is 30 cm deep and 30 cm wide, a staircase of one salt-finger layer and one convecting layer develops for a certain setting of the control parameters. The convecting layer has \(A \simeq 2\). Shadowgraphs show convecting plumes that appear disorganized, and a large-scale flow never develops. Instead, the finger layer grows in height, overtakes the convecting layer and within a few days becomes one finger layer. The second tank (the ‘\(1 \times 5\)’ tank) is also 30 cm deep but is 150 cm wide. For the same control parameter setting a similar staircase with a finger layer 20 cm deep and a convecting layer 10 cm deep develop. The convecting layer, with \(A = 15\), has quite a different character. A large-scale flow develops so that the convecting layer has one cell, 10 cm deep and 150 cm wide. In this flow are large plumes which are transient and tilted; particle image velocimetry measurements of Reynolds stresses show they help to maintain the large-scale flow against viscous dissipation. Shadowgraphs show all the finger tips swept in the direction of the large-scale flow adjacent to the finger layer. Measurements show that the large-scale flow ‘collects’ the salt delivered by the many fingers so that the accumulated negative buoyancy leads to deep convection. This is a more stable arrangement, with the configuration lasting to the order of \(10^2\) days.


76-05 Experimental work for problems pertaining to fluid mechanics
76R50 Diffusion
80A20 Heat and mass transfer, heat flow (MSC2010)
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