On the arrested development of the Rayleigh Taylor instability with and without cabbeling*

Cabbeling, the phenomenon in which fluid parcels of the same density but different temperatures can mix to form a fluid parcel that is denser than its parents, commonly occurs in natural waters in late winter and early spring. We consider the classical Rayleigh Taylor instability in the cabbeling regime. Using three dimensional numerical simulations we track the instability into a mature quasi-turbulent regime. In the case of no cabbeling, the development of the Rayleigh Taylor instability is rapidly arrested by instability-induced mixing. In contrast, cabbeling allows the fluid to reach a self-sustaining regime in which cabbeling produces denser fluid that continues to drive further instability. By varying the proximity of the initially unstable interface to walls we demonstrate that very different regimes can be achieved in terms of the distribution of temperature and kinetic energy in the quasi-turbulent region. Finally, we discuss the distribution of the viscous dissipation, finding that while the flow regime is vortical, chaotic and efficiently mixing, no well-defined inertial subrange exists.