This thesis presents a numerical and experimental study of the interaction of shock waves with air-filled cavities in a liquid. At the incident shock pressures studied, this process leads to the formation of high-speed jets which propagate across the cavities, causing them to collapse. This phenomenon is modelled numerically using a front-tracking approach, which enables explicit tracking of the gas-liquid interface. In arrays of multiple cavities, this method is used to show that inter-cavity effects can lead to intensification of the collapse process under certain conditions. A number of different arrangements are presented, demonstrating that in all cases the separation distance between the cavities and the relative radius of the cavities are of key importance. This result is highlighted with the study of an array of three cavities, in which it is shown that pressures over five times higher than the maximum pressure observed in the single cavity case may be achieved. Experimentally, a single stage light-gas gun is utilised to create strong shock waves in hydrogel blocks, into which spherical cavities are cast. With this setup, high-speed imaging and optical diagnostics are used to show that cavities collapse as predicted numerically, and that light is emitted upon collapse. In the single cavity case, this light is formed initially at the position at which the high-speed jet strikes the far cavity wall, propagating out subsequently into a torus. The spectral intensity of the light emission increases consistently with increased incident shock pressure. In multiple cavity arrangements, the complex inter-cavity effects seen numerically are found to be substantiated by experimental results. The spectral intensity of the light emission is seen to vary significantly with the separation distance between the cavities, with order of magnitude increases observed for particular cases.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:719890 |
| Date | January 2015 |
| Creators | Betney, Matthew R. |
| Contributors | Roy, Ronald A. ; Ventikos, Yiannis |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:80ccb37e-ef92-4d74-bf28-ec7e238da491 |
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