Numerical And Experimental Research Of Bubble Behavior In Restricted Space

Bubble is a common phenomenon in liquid. Vapor bubbles are formed by cavitation due to the decrease of local pressure, which will develop, collapse and rebound in the liquid. Other bubbles consist of external gas entrapped in the liquid, which play an inportant role in cavitation process as cavitation nuclei. Bubble causes several serious problems in fluid systems, such as vibration, noise and cavitation erosion. On the other hand, bubble can be widely applied in the areas of medical treatment. MEMS and engineering, while it is also a pivotal element in many natural processes. Although bubbles have attracted attention of many reaseachers. investigation on the behavior of bubbles in restricted space is uncommon in literature.In this thesis, the behavior of bubbles in restricted space is studied systematically and comprehensively, by means of theoretical analysis, numerical simulation and high-speed camera observation. The phenomena of bubble entrainment during drop impacting on restricted liquid surface are summarized. The effects of the restircting wall and the vibration of drop are analysised. The regimes of various outcomes of drop impact are given on non-dimentional parameter plane. The collapse of antibubble is studied quantitatively, to derive a model of the collapse velocity. The dynamic behavior of single/double spark-induced bubble in tube is observed by high-speed camera. BEM numerical model for the bubbles in tube is presented, with which the effect of tube wall on the behavior of the bubble is presented, and mechanism of single/double spark-induced bubble in tube is analysised.The outline of this thesis is as follows,In chapter1, the background and significance of the thesis are proposed. Literature on the bubble formation during impacting process and the dynamics of cavitation bubble are reviewed. The main content of the thesis is summarized.In chapter2, BEM numerical model for the dynamic behavior of bubbles is presented, which is able to deal with bubble coalescence and ring bubble. The governing equations, boundary integral equations, descretization. calculation programme and other algorithms are introduced.In chapter3, the phenomena of bubble entrainment during drop impacting on restricted liquid surface are summarized into four types. The regimes of various outcomes of drop impact are given on parameter plane. The effects of restricting wall on delayed bubble, large bubble and canopy bubble are analysised. The discrete Weber number regime of large bubbles is reported, which is caused by the shape oscillation of the drop. A model of the collapse velocity of antibubbles is derived, which shows that the collapse velocity is proportionate to (σ/pe)1/2.In chapter4, the development and collapse of single spark-induced bubble in tube is studied, whose volume and vibration period are analysised by numerical simulation. The interaction of two spark-induced bubbles is observed by high-speed camera. The mechanism of two bubble interaction is analysised, and the regimes of various phenomena are presented on parameter plane.In chapter5, the research work of the thesis is summarized with further prospect.