Implosion of longitudinally off-centered cylindrical volumes in a confining environment

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A comprehensive experimental/numerical study on the implosion of longitudinally off-centered cylindrical implodable volumes was conducted within a tubular confining space. In particular, the aim of this study was to examine the changes in the implosion mechanics and in the nature of pressure waves, arising from the longitudinally off-centered location of the implodable volume. Experiments were conducted with 31.8mm outer diameter, cylindrical aluminum 6061-T6 implodable volumes placed concentrically within the confining tube. Three longitudinal offset locations were chosen within the confining tube, such that distance from the center of the implodable volume to the center of confining tube is equal to: (a) zero, (b) 3/7 of the half-length of confining tube (L), and (c) 5L/7. Pressure transducers mounted on the inner surface of the confining tube were used to capture the pressure waves released during the implosion event. Computational simulations were performed using a coupled Eulerian-Lagrangian scheme to explicitly model the implosion process of the tubes along with the resulting compressible fluid flow. The experiments revealed that the longitudinal asymmetric placement of the implodable volume enhances the strength of hammer pressure waves generated during the implosion process. The off-centered location of the implodable volume causes a pressure imbalance in the entire length of the confining tube. Hence, the water particle velocity shifts toward the implodable volume producing high pressure region at the end-plate near the implodable volume, while the other end-plate experiences significantly longer cavitation due to low pressure. This far end-plate cavitation duration is also found to increase with increasing longitudinal offset, even though the total combined cavitation duration at both the end-plates is approximately same for all offset locations. With high correlation observed between the experiments and simulations, computation models were further used to correlate the longitudinal offset and the signature of pressure waves at various interpolated locations. Simulations show that there is increase in both the peak pressure and the impulse of the hammer wave with increasing longitudinal offset of the implodable volume. Simulations also show that the collapse rate of the implodable volume decreases with the increasing longitudinal offset.

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Journal of Applied Mechanics, Transactions ASME