| Bubbles exist in nature and many industrial processes, especially in energy, chemistry and environment engineering. The phenomena of bubble can be found easily in many practical applications, for example, the cavitation and cavitation erosion of water turbine and water pump, the fluid flowof ship propeller, gas-liquid chemical reaction and wastewater treatment etc. The behaviors of bubble dynamics have direct effects on momentum, heat and mass transfer of multiphase flows directivel, so the research on bubble behaviors has attracted more and more attention in China and abroad.The interface tracking for two-phse flow is a fundamental research subject with wide applications. Especially research on disciplinarian of bubble motion is a subject with large chalange.But in practical engineering, the environment of bubble being is much conplex that it is needed to deal with the boundary conditions for complex physical domain. In order to solve this problem, the Level set method is applied to body-fitted coordinates (BFC) for tracking interface in a physical domain with complex boundary conditions with higher accuracy. Basing on this, the dynamic characteristics of bubble moving in regular and complex channel is studied in this article. The main works of this part and conclusions included are as follows:1. Using the Level set approach in BFC, the author simulated the single bubble rising in liquid, bubble rising near to interface and In-line bubbles coalescence respectively. The SIMPLE algorithm is employed to decouple velocities and pressure and the surface tension is considered as a volume force with CSF model. As a result, the bubble is simulated exactly and the changes of bubble shapes, positions and veocities are gotten. In addition, the program is extended to 3-dimension well with a satisfied result.2. Developed Level set method in BFC and simulated the motion of buoyancy bubble in complex channel. The volume-modified Level set method in BFC is used to deal with non conservation of bubble volume and the reinitialization method with narrow band is conducted to solve the numerical dissipation caused by mesh nonorthogonality. Basing on this, the bubble rising in a vertical channel with wedge shaped throat is simulated and the shapes evolution and changes of parameters, such as vertical velocity, horizontal velocity, aspect ratio and inclining angle of bubble are studied. In addition, the program is extended to 3-dimension well with a satisfied result. 3. Applying Level set method and SIMPLE method on the collocated grids in BFC to simulate bubble motion in wedged orifice flowmeter. As a result, the main two influencing factor to measuring accuracy of wedged orifice flowmeter is provided by analysis as:changes of mixture density on limited section and pressure difference between tapping pipes. The former is the dominant one to effect on measuring accuracy. So an instrument which can measure the mixture density of the liquid correctly is needed to improve the measuring accuracy and minish the error in measuring the fluid flux with wedged orifice flowmeter.Early studys on bubble dynamincs are employing on photography. In recent years, with the development of photography, it is possible for people to obtain an accuracy and clear image of bubble and it makes this method to be used more widely and deeply in fields of bubble dynamics.High speed photography is a direct, cheap and effective means of study air bubbles in liquid which is developed in recent years. With the help of high-speed digital camera, bubble dynamincs is study in regular and complex channel in this article.1. Employing the high speed digital camera, the auther shoots and tracks the bubble motion in vertical wedge shaped channel to obtain the dynaminc characteristics of bubble motion in wedge shaped channel, such as variation of bubble's velocity, acceleration and rotating angle etc. and abstract the formula of bubble's drag coefficient in wedge shaped channel.2. Employing the high speed digital camera, the author shot the behavior of a rising soluble bubble through the quiescent solution synchronously. By image-processing to the image obtained in observation experiment, the author find that the heat transfer of small bubble in gas-fluid flow is dominant factors which affects bubble's moving.
|
PDF Full Text Request