Parallel Water Entry: Experimental Investigations of Hydrophobic/Hydrophilic Spheres
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E?RCOFTAC Spring Festival 2023
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This presentation describes the experimental setup on parallel and simultaneous water entry (WE) of two spheres into water and provides an overview and a discussion of the results obtained for hydrophilic and hydrophobic spheres. The physics of WE and of parallel WE is important for a variety of engineering and natural science applications, such as underwater or navy vehicles, marine platforms such as floating offshore wind turbine platforms, invasive free-surface flow measurement devices used in the steel industry, coating and spraying processes, synchronized-diving athletes or plunge-diving birds, etc. Scientific research in this area may lead to measures to reduce slamming loads on marine vessels and platforms, improve the accuracy of free-surface instrumentation, or even explain, why a diving bird does not get injured when it collides with water at high speed. Parallel WE is a highly nonlinear and unsteady process and the interactions influence air entrainment cavities and pinch-off (which can strongly affect the impact forces and the objects' kinetics) as well as splash curtains and jets (often undesired in engineering applications). Using High-Speed-Cameras and image processing techniques the parallel WE of hydrophilic/hydrophobic spheres and the interaction of the involved physical phenomena is investigated. This project is funded by the EU-H2020 Marie Sk?odowska-Curie Individual Fellowship programme. The results presented give an overview of the first phase of the project, where the influence of sphere distance and impact velocity was studied for different pairings of hydrophilic and hydrophobic spheres. Video sequences and images of cavity and splash curtain formation and development as well as evaluation data on sphere trajectories, sphere velocities and the cavity pinch-off points are presented for a selected number of cases.