Experimental study of Atwood number effects on the single-mode Rayleigh-Taylor instability

The growth of Rayleigh-Taylor (RT) spikes are studied experimentally for a single-mode, 2D initial condition. The experiments are performed using a magnetorheological (MR) fluid, composed of 4.5 micron spherical iron particles suspended in hexane with a small amount of oleic acid used as a surfactant. This mixture is suspended over aqueous salt solutions to achieve different Atwood number fluid pairs between 0.2 and 0.5. A discontinuous, membrane-less, and initially static interface is created by magnetically immobilizing the MR fluid while resting over ice of a prescribed shape. This technique results in a well defined initial perturbation. The temporal growth of the spikes is observed with a back-lit, high speed imaging system, and growth rates obtained from these experiments are compared with published analytical, experimental, and numerical results. The transition from linear to non-linear growth is also examined and compared with analytical predictions using the approach attributed to Fermi by Layzer.