Development and Assessment of Methods for the Prediction of Hydrodynamic and Ultrasound induced Cavitation
Sammanfattning: The cavitation phenomenon has today become a keystone for different areas of science and technology including various industrial processes and medicine. Recently increasing interest and much attention have been paid to study this phenomenon. The last two decades have witnessed the development of numerous devices for different important applications of considerable practical interest, and the range of these applications is in continuous increase. This thesis aims to gain more knowledge about the mechanisms and dynamics of the cavitation phenomenon. In the present study, various techniques are developed and investigated. The major principal parameters associated with these phenomena are all presented in order to improve and give more comprehensive understanding of the phenomenon. The study presents enhanced numerical models to analyze the cavitation phenomenon and simulated results of formation and collapse of a single bubble in a liquid are provided. A convenient model is applied and its enhancements are examined numerically. The validity and comparison with the available experimental data were found favorable. The model is employed to deduce the bubble dynamics in flow domains for the following situations, 1. Bubble dynamics in an acoustic field. The sound waves create pressure variations through the medium and cause regions of rarefaction and compression. These pressure variations can set a tiny bubble into radial motions, i.e., expansion and compression. The bubble in an acoustic field grows as the pressure associated with the sound waves gives rarefaction. When the pressure turns to compression, the bubble is compressed and may reach an unstable size and then collapse violently. During this process, the nonlinear motion of the bubble is a complicated process. Despite many efforts, the demand of creating more suitable models with a realistic applicability calls for numerical calculations of the bubble motion in an acoustic field. This will provide improved knowledge about the real situation and the main results associated with this phenomenon. 2. Bubble dynamics close to a rigid boundary. In fact, the simulation of non-spherical bubble dynamics and its interaction with solid boundaries has received much less attention due to the complexity of the problem. A main reason of the structural damages in the cavitation phenomenon is due the formation of micro jets generated due to the bubble collapse and impingement on the solid surfaces or boundaries. The boundary integral method (BIM) is employed to compute the bubble motion and explosion of a cavitation bubble close to a rigid boundary. The liquid is considered to be incompressible, inviscid, and irrotational around the bubble. These assumptions satisfy the conditions for the Laplacian equation.
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