Energy equipartition in stratified flows?

We seek to understand the net energy conversion between quiescent initial and final states in a miscible variable density system. The particular configuration we examine is a Rayleigh-Taylor unstable interface in an otherwise linearly stably stratifed brine solution and our experiments measure vertical profiles of density before and after the unstable interface is allowed to relax to a stable state. Our analysis suggests that ex- actly half the initially available energy is released as heat due to viscous dissipation, while the other half changes the structure of the density field by scalar inter-diffusion and is thereby re-absorbed as potential energy in an un-available form. While we observe this equipartition property in many Rayleigh-Taylor driven mixing flows, our new configuration admits energetically consistent end-state density profiles where less energy could be dissipated as heat and more could be re-absorbed into potential en- ergy, or vice versa. Our experiments show that the fluid maintains equipartition of energy, despite the flexibility to do otherwise. We conclude that this is a physical property of the fluid rather than a geometric property of the configuration.