Turbulent layer dynamics in stratified Taylor-Couette flow

Abstract eng:
We describe a series of laboratory experiments to study the turbulent mixing dynamics of an initially linear stratification in Taylor-Couette flow, i.e. the flow in the annular region between two concentric cylinders. As described in [1], relatively well-mixed layers separated by substantially thinner ‘interfaces’ of enhanced density gradient spontaneously form. Consistently with [1], these layers are extremely long-lived, and exhibit an average turbulent buoyancy flux that falls on a ‘universal’ curve independent of the number of the layers. However, by high-frequency measurements of density and image analysis, we show that the ‘interfaces’ are highly spatially and temporally intermittent, and for sufficiently small separation between interfaces, there is a dynamically robust, and profoundly nonlinear coupling between neighbouring interfaces. Such robust spatio-temporal intermittency has significant implications for the quantification and parameterisation of mixing driven by horizontal shear, as commonly arises in the environment.

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