Study of the membrane effect on turbulent mixing measurements in shock tubes

The effect of the thin membrane on the time evolution of the shock wave ind uced turbulent mixing between the two gases initially separated by it is in vestigated using two different sets of experiments. In the first set, in wh ich a single-mode large-amplitude initial perturbation was studied, two gas combinations (air/SF6 and air/air) and two membrane thicknesses were used. The main conclusion of these experiments was that the tested membrane has a negligible effect on the evolution of the mixing zone, which evolves as p redicted theoretically. In the second set, in which similar gas combination s and membrane thicknesses were used, small amplitude random-mode initial p erturbation, caused by the membrane rupture, rather than the large amplitud e single-mode initial perturbation used in the first set, was studied. The conclusions of these experiments were: (1) The membrane has a significant e ffect on the mixing zone during the initial stages of its growth. This has also been observed in the air/air experiment where theoretically no growth should exist. (2) The membrane effect on the late time evolution, where the mixing zone width has reached a relatively large-amplitude, was relatively small and in good agreement with full numerical simulations. The main conc lusion from the present experiments is that the effect of the membrane is i mportant only during the initial stages of the evolution (before the re-sho ck), when the perturbations have very small amplitudes, and is negligible w hen the perturbations reach relatively large amplitudes.