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The propagation of full-depth lock-exchange bottom gravity currents past a submerged array of circular cylinders is investigated using laboratory experiments and large eddy simulations. Firstly, to investigate the front velocity of gravity currents across the whole range of array density
(i.e. the volume fraction of solids), the array is densified from a flat bed (
) towards a solid slab (
) under a particular submergence ratio
is the flow depth and
is the array height. The time-averaged front velocity in the slumping phase of the gravity current is found to first decrease and then increase with increasing
. Next, a new geometrical framework consisting of a streamwise array density
and a spanwise array density
is proposed to account for organized but non-equidistant arrays (
are the streamwise and spanwise cylinder spacings, respectively, and
is the cylinder diameter. It is argued that this two-dimensional parameter space can provide a more quantitative and unambiguous description of the current–array interaction compared with the array density given by
. Both in-line and staggered arrays are investigated. Four dynamically different flow regimes are identified: (i) through-flow propagating in the array interior subject to individual cylinder wakes (
: small for in-line array and arbitrary for staggered array;
: small); (ii) over-flow propagating on the top of the array subject to vertical convective instability (
: large); (iii) plunging-flow climbing sparse close-to-impermeable rows of cylinders with minor streamwise intrusion (
: large); and (iv) skimming-flow channelized by an in-line array into several subcurrents with strong wake sheltering (
: small). The most remarkable difference between in-line and staggered arrays is the non-existence of skimming-flow in the latter due to the flow interruption by the offset rows. Our analysis reveals that as
increases, the change of flow regime from through-flow towards over- or skimming-flow is responsible for increasing the gravity current front velocity.
Experiments with layers of salt and sugar solution separated by
a diffusive interface
are described. Interfacial waves were spontaneously generated by the convection
once the system evolved to a critical value of the density-anomaly ratio
The waves locally modulated the interfacial fluxes by modifying the
interface thickness and thereby organized otherwise random convective motions
large-scale circulations. In turn, the waves themselves persisted for unusually
times owing to energy input from the organized convection. The dependence
wave speed on the layer properties and channel dimensions was successfully
by assuming that coupling requires a matching of the wave and convection
that the system selects waves of an amplitude for which this resonance
can occur. This
‘wave–convection coupling’ also appeared to
increase the interfacial fluxes at low Rρ.
The interaction of waves and convection may be important for oceanic thermohaline
staircases and other systems where convection is driven by interfacial
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