Turbulent mixing in stratified centrifugally unstable Taylor-Couette Flow

We investigate the mixing in an axially stably stratified turbulent Taylor-Couette (STC) flow. STC is prone to the `stratio-rotational instability’ (SRI) even when the flow is centrifugally stable. Conversely, for the centrifugally unstable flow at high rotation rates, the flow spontaneously forms layers for an initially linear stratification, separated by robust interfaces. It was previously observed by Oglethrope et al. (2013) that the flux across the interface in a two-layered experiment with only inner cylinder rotating at a constant frequency Ω, stays constant with reducing Richardson number (Ri∝ Δρ_interface), until a critical Ri where the flux starts to increase. Using particle-image-velocimetry (PIV), we demonstrate that this enhanced flux is due to the onset of micro-splashing of fluid from near the inner cylinder onto the region of outer cylinder near the interface. Also, these interfaces appear to support m = 1, inherently nonlinear perturbations with a characteristic period which depends only on Ω. Using PIV and laser-induced fluorescence (LIF), we characterise the flow behaviour, and in particular the mixing mechanisms due to these coherent perturbations.