UWFDM-1172 Experiments on the Richtmyer-Meshkov Instability II: Nonlinear Evolution of a Shocked Membraneless Single-Mode Sinusoidal Interface

An experimental investigation of the shock-induced interfacial instability (RichtmyerMeshkov instability) is undertaken in an effort to study temporal evolution of interfacial perturbations in the nonlinear regime. The experiments are performed in a vertical shock tube with a square cross-section. A membraneless interface is prepared by retracting a sinusoidally shaped metal plate initially separating carbon dioxide from air, with both gases initially at atmospheric pressure. With carbon dioxide above the plate, the Rayleigh-Taylor instability commences as the plate is retracted and the amplitude of the initial sinusoidal perturbation imposed on the interface begins to grow. The interface is accelerated by a strong shock wave (M=3.08) while its shape is still sinusoidal and before the Kelvin-Helmhotz instability distorts it into the well known mushroom-like structures, but its amplitude to wavelength ratio is large enough that the interface evolution enters its nonlinear stage very shortly after shock acceleration. The pre-shock evolution of the interface due to the Rayleigh-Taylor instability and the post-shock evolution of the interface due to the Richtmyer-Meshkov instability are visualized using planar Mie scattering. The pre-shock evolution of the interface is carried out in an independent set of experiments. The initial conditions for the RichtmyerMeshkov experiment are determined from the pre-shock Rayleigh-Taylor growth. In this article we describe the Richtmyer-Meshkov experiment in detail. One image of the post-shock interface is obtained per experiment and image sequences, showing the post-shock evolution of the interface, are constructed from several experiments. The growth rate of the perturbation amplitude is measured and compared with some of the most recent nonlinear analytical models of the Richtmyer-Meshkov instability.