Numerical investigation on high velocity liquid dynamics

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This thesis examines the dynamics of high-velocity liquid-gas flows, focusing on medical inhalers and their applications. It explores liquid dynamics within inhalers—critical for treating asthma and COPD—using simulations, especially the Volume of Fluid (VoF) method for compressible effects, due to experimental challenges at high velocities. Large-Eddy Simulations (LES) assess the annular liquid jet in inhalers, uncovering its oscillatory behavior influenced by the supersonic gas jet's velocity and pressure. This is evident in how nozzle diameter affects liquid flow oscillation frequency and the jet's radial distribution. The study also analyzes transient convective instability in liquid sheets affected by supersonic gas, using dynamic mode decomposition and proper orthogonal decomposition (POD) to identify key topological features and the interplay between momentum and pressure fields through transfer entropy. Additionally, it models droplet impacts on cylindrical pillars, proposing a new analytical model for impact pressure and droplet behavior to predict cavitation enhancement. Simulations reveal that droplet impact compresses the liquid, causing lateral jetting and cavitation through shock wave interactions, challenging traditional low-velocity impact models. The new model, incorporating lateral jetting's characteristic length, improves predictive accuracy over existing methods.

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Yanchao Liu

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