To address difficulties in treating large volumes of liquid metal with ultrasound, a fundamental study of acoustic cavitation in liquid aluminium, expressed in an experimentally validated numerical model, is presented in this paper. To improve the understanding of the cavitation process, a non-linear acoustic model is validated against reference water pressure measurements from acoustic waves produced by an immersed horn. A high-order method is used to discretize the wave equation in both space and time. These discretized equations are coupled to the Rayleigh-Plesset equation using two different time scales to couple the bubble and flow scales, resulting in a stable, fast, and reasonably accurate method for the prediction of acoustic pressures in cavitating liquids. This method is then applied to the context of treatment of liquid aluminium, where it predicts that the most intense cavitation activity is localised below the vibrating horn and estimates the acoustic decay below the sonotrode with reasonable qualitative agreement with experimental data.

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The Cold Crucible, or Induction Skull Melting process as is otherwise known, has the potential to produce high purity melts of a range of difficult to melt materials, including Ti-Al alloys for Aerospace, Ti-Ta and other biocompatible materials for implants, Silicon for photovoltaic and electronic applications, etc. Induction currents melt the alloy in the crucible and partially suspend it away from water-cooled surfaces. Strong stirring takes place in the melt due to electromagnetic forces and very high temperatures are attainable under the right conditions. In a joint numerical and experimental research programme, various aspects of the design and operation of this process are investigated to increase our understanding of the physical mechanisms involved and to maximise efficiency. A combination of FV and Spectral CFD techniques are used at Greenwich to tackle this problem with the experimental work taking place at Birmingham University. Results of this study presented here, highlight the effects of turbulence and free surface behaviour on attained superheat and also discuss coil design variations and dual frequency options that may lead to winning designs.