Optimal mixing flows: mechanisms and measurements

12 March 2013, 12.00 PM - 12 March 2013, 12.00 PM

Venue: QB1.7. Speaker: Dr Andrew Lawrie, Department of Mechanical Engineering
Rayleigh-Taylor instability is the transient buoyancy/inertia-driven process that occurs when more dense fluid overlies lighter fluid. Conceptually, the configuration could hardly be simpler, yet it has provided enough puzzlement for scientists to motivate over a century of research. 

Lord Rayleigh first considered the problem in 1883, but his experiments had inadvertently uncovered a separate diffusion driven instability. 

Independently, in 1950, G.I. Taylor published the first theoretical work on the buoyancy-inertia instability, which we now call after both Rayleigh and Taylor. Taylor's theory is only valid over the short time-scales that linear theory is applicable, thereafter, the non-linearities dominate. An enormous collection of research on the non-linear development has been amassed, but with relatively little consensus on even the most basic issues.

The key question is how fast the instability grows, and understanding this requires us to examine how energy is spent as the system relaxes. Rayleigh-Taylor driven processes are arguably optimal mechanisms for mixing, but experimental measurements of the classical instability have historically misled our understanding of these mechanisms.

This talk will present an approach which enables us to isolate and measure the optimal mixing that characterises Rayleigh-Taylor instability, and from this we can deduce the redistribution of energy as the system relaxes.

Lunch will be provided outside QB 1.7 from 12:30pm

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