UWFDM-1171 Experiments on the Richtmyer-Meshkov Instability I: Preparation of a Membraneless Interface Using the Rayleigh-Taylor Instability

A large number of experimental investigations of the Richtmyer-Meshkov instability (a shock-induced interfacial instability) in the past have been carried out in shock tubes. In order to separate the two gases prior to the shock arrival, a plastic membrane, on the order of one micron thick, was often used. There is considerable uncertainty regarding the effects of the membrane and membrane fragments present in the postshock flow-field. Some investigators have attributed the lack of agreement between the experimental and numerical results to the presence of membrane fragments while some recent investigations report negligible effect of the membranes on the development of the R-M instability. Furthermore, it was postulated that for strong incident shocks, the membrane would pyrolyze and act as a continuous gaseous interface between the two gases under investigation, thus minimizing its undesirable effects. In the present experimental campaign, we investigate the interaction of strong shocks (M > 2) with nitrocellulose and mylar membranes. We conclude that the membrane fragments do not undergo pyrolysis and while their effects are not apparent in line-of-sight integrated optical techniques such as schlieren and shadowgraphy, they are evident when the flow-field is interrogated using a two-dimensional planar diagnostic technique. In order to create a membraneless interface, a novel technique is developed which involves retracting a thin metal plate formed into a sinusoidal shape, initially separating the two gases. Plate retraction is followed by the development of the Rayleigh-Taylor instability, leading to an interface shown by Mie scattering visualization to exhibit a repeatable, predominantly single-mode sinusoidal shape.