Visual Experiment Research Of The Bubble Near The Wall

Cavitation is a common phenomenon in the fluid system. When the internal pressure or stress in the fluid reduces to a critical value, violent gastification appear in the fluid and a large number bubble can flow. It could be called the caviation phenomenon as distinguished from boiling phenomenon. Caviation was followed flow blockage with the reduction of the system efficiency. Vibration and noise will appear and even cause the mechanical or chemical damage in the system. It should be avoided in the hydraulic system, turbine machinery and hydro-structure. With the development of the technology and expansion of the human activities, the area of cavitation is increasing such as biomedical, nuclear energy and aerospace. Cavitation has become a basic scientific problem in the human practice activities which is needed to face and further understandings.High temperature, high pressure and high speed jet will generate in the collapse point while the cavitation bubble collapse near the boundary. The high temperature and high pressure induced by the cavitation bubble collapse is utilized to speed up chemical reactions or achieve the tiny particle drive. Mechanical behavior of the bubble near the wall is an important component of the bubble dynamics. Much research has focused on the rigid wall. In the recent years, along with the cavitation application in the biomedical area going much further, the research of the bubble near the elastic boundary and in the tube also gradually unfolded.The thesis concentrates on a systematic study on bubble behavior near the wall and related application through the theory analysis, numerical simulation and experimental observation. By means of the high speed observation, the paper analyse wall distance, bubble size and elastic wall that influence the bubble mechanical behavior and reveal the critical condition of external inducing the jet change-of-direction and the coupling relation between wall and bubble. Quantitative analysis of the two bubble jet behavior is carried on and the interation rule between the bubble and wall is revealed. The thesis develops applied research on the bubble dynamic behavior in the tube and establishes the energy transfer model of the cavitation jet in the tube, which is verified in the particle removal experiment. The outline of this thesis is as follows:In chapter1, Introduction, The research situation of single bubble and multiple bubbles cavitation dynamics is introduced. The research progress of the cavitation bubble in the biomedical area and the high speed camera technology in the fluid area is briefly stated.In chapter2, the foundation of cavitation dynamic and numerical calculation, the spherical bubble dynamic is stated. The full boundary element method is introduced which is used to simulate the interaction of the bubble with the elastic boundary and it maybe the most versatile method for transient bubble dynamic simulation. The spherical bubble collapse process is simulated with the Rayleigh model and the effect of liquid viscosity is investigated also. The single bubble model is built under the confined space condition and the influence of the confined space dimension on the bubble collapse is studied.In chapter3, the bubble experimental system, the bubble experimental system is structured. The single bubble is generated by the experimental setup. The bubble collapse in a free field is studied and the result is compared with the numerical result. Two bubbles interaction in the free field is investigated by the experiment which is compared with the previous experimental results.In chapter4, the bubble behavior near the wall, the bubble interaction with the elastic boundary is investigated. The influence on the bubble dynamic behavior of the distance between the bubble and the boundary is analyzed and the quantitative relationship between the bubble distance and the elastic boundary deformation is given. The dimensionless distance between the two bubbles γ and the dimensionless distance between the bubble and the boundary γb are defined. The γ value and γb value influence on the bubble jet behavior is investigated and the critical condition for jet chang-of-direction is present. The effect of the elastic tube on bubble behavior is studied and the accompanied cavitation phenomenon in the tube is observed in the experiment.The theory model of the bubble collapse in the tube is built and the simulation research is conducted. The model prediction results are compared with the experimental results. The effect of the tube diameter on the bubble collapse is considered and the boundary deformation amount with the tube diameter is plotted.In chapter5, the cavitation jet and its application, the micropump effect inducing by the bubble collapse achieve the fluid delivery. The liquid drop formation dynamic process is revealed by the high speed camera and the liquid drop formation velocity is affected by the distance between the plate and the bubble. The particle removal by the bubble-induced jet which contains the particle removal in the tube and in the tube end is investigated by the experiment method. The effect of the distance between the bubble and particle is quantitative analyzed and the energy transfer model of the cavitation jet in the tube is built. The mathematic relation between the particle velocity and liqid viscosity is revealed. The numerical result result is compared with the experimental result.In chapter6, conclusions and prospection, the main research work of this thesis and the innovation of the thesis are summarized.