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UBC Theses and Dissertations

Numerical and experimental investigation in the instability and the breakup of capillary water jet Moallemi, Nima


In this thesis, the instability and breakup of free capillary jets are investigated. Both numerical and experimental methodologies are used to define the breakup process for capillary jets. High speed photography is used to capture droplet formation and to measure breakup length. In parallel, numerical simulations based on the volume of fluid (VOF) approach, with interface tracking and adaptive meshing are performed to provide further insight into the jet instabilities. The VOF method enables accurate tracking of the interface while reducing computational cost by means of adaptive grids. The growth rate of disturbance is compared with the theoretical prediction from a dispersion relation obtained by first-order perturbation analysis. Moreover, the numerical results show a good agreement with experimental data for the breakup length of the liquid jet under different wave numbers. The velocity profile and the pressure gradient in the necking zone of the jet are analyzed to clarify the droplet detachment process. In addition, Lagrangian analysis of fluid particles in the jet shows that when droplet detachment occurs, the direction of fluid particles changes dramatically due to droplet oscillations.

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