Jr. Taylor et G. Veronis, EXPERIMENTS ON DOUBLE-DIFFUSIVE SUGAR-SALT FINGERS AT HIGH-STABILITY RATIO, Journal of Fluid Mechanics, 321, 1996, pp. 315-333
In a series of laboratory experiments the growth of double-diffusive s
alt fingers from an initial configuration of two homogeneous reservoir
s with salt in the lower and sugar in the upper layer was investigated
. For most of the experiments the stability ratio was between 2.5 and
3, where the latter value is at the upper limit (the ratio of salt to
sugar diffusivities) for which fingers can exist. In these experiments
long slender fingers are generated at the interface. Essentially all
theories or physical bases for models of salt fingers presuppose such
a configuration of long fingers. Our measurements show that the length
of fingers at high stability ratio increases with time like t(1/2), w
ith a coefficient that is consistent with the diffusive spread of the
faster diffusing component (salt). When the initial stability ratio is
closer to unity, fingers penetrate into the reservoirs very rapidly c
arrying with them large anomalies of salt and sugar which give rise to
convective overturning of the reservoirs. The convection sweeps away
the ends of the fingers, and when it is intense enough (as it is when
the sugar anomaly is large) it can reduce the finger height to a value
less than the width. After this initial phase the finger length grows
linearly with time as has been found in previous studies. These resul
ts show that salt fingers can evolve in quite different ways depending
on the initial stability ratio and must cast doubt on the use of simp
le similarity arguments to parameterize the heat and salt fluxes produ
ced by fingers.