Experimental measurements of the nonlinear Rayleigh-Taylor instability using a magnetorheological fluid.

The unique properties of magnetic fluids are exploited to create a static interface between two fluids in the context of studying Rayleigh-Taylor (RT) driven mixing. Paramagnetic fluids have previously been used for studying this phenomenon [Z. Huang, Phys. Rev. Lett. 99, 204502 (2007)], as have ferrofluids [G. Pacitto, Phys. Rev. E 62, 7941 (2000)], but we propose using magnetorheological fluids instead to attain better control of the initial condition. As the motivation for using this technique is to quantify the effects of the initial condition on late time behavior of the RT instability, it is important that the initial condition be prescribed at a scale large enough to reliably measure. As a first demonstration of creating such an interface, this technique is applied to the two-dimensional (2D) instability with a single-mode sinusoidal interface. This technique has been used to study both moderate and high Atwood number systems, with successful control of the interface in an A=1 system being demonstrated. The nonlinear growth phase for this initial condition is examined and comparisons are made with both analytical models and published numerical and experimental work on the 2D single-mode RT instability. Measurements of the late time RT spike behavior reveal poor agreement between the experimental results and the analytical models.