Study Of Interaction Between Free Surface And Moving Object

The flow with free surface is a very common phenomenon, such as the motion of wave caused by wind and cavitation around the high speed submerged vehicle. Among them, cavitation process widely exists in operation process of underwater equipment, which will produce noise and vibratioin, even case cavitation erosion. Therefore, it is of great significance to study the flow process of free surface, especially cavitation.This article numerically studies the interaction between the water surface, cavity and body by using the commercial software Fluent. The first part studies the collapse process of bubble under kinds of boundary conditions, including unbounded domain, solid wall, free surface and composite boundary of solid wall and free surface. The second part numerically studies the submerged body exiting from water vertically with cavitation. The effect of velocity, acceleration and local cavitation number on the cavitation development and the pressure distribution on the submerged body is stated. The last part numerically studies the submerged body exiting from water obliquely with cavitation. The influence of velocity and asymmetry on the cavities near the shoulder and bottom of the body is discussed respectively during the stage of growth and collapse. By data collection and analysis, the main conclusion is as follows:1. The simulation result of one bubble collapsing in unbounded domain and near the solid wall and free surface is compared with the simulation and experiment result in the past. The effectiveness and accuracy of the numerical method of this paper is verified. In addition, during the collapse of a bubble near the composite boundary of solid wall and free surface, the effect of free surface is dominant to the bubble sinking direction, then the effect of solid wall is increasing and plays leading roles at the last stage of collapse.2. For the vertical water exit of submerged body with conical head in non-uniform velocity, within the scope of parameter in the simulation, the development of bubble can be devided into three stage: the stage of first growth, the stage of second growth, the stage of collapse. The quasi-steady feature in the stage of second growth is obtained in different mode of motion. During the stage of collapse, for the water exit in accelerated motion, the cavity on the shoulder moves downward relative to the body, even combine with the cavity on the bottom, while for the water-exit in constant speed and decelerated motion, the location of the end of the cavity is unchanged.3. For the oblique water exit of submerged body in non-uniform velocity, during the stage of growth, for the water exit in accelerated motion, the cavities on the shoulder and on the bottom is easily combined, while for the water-exit in decelerated motion, they are not combined. During the stage of collapse, for the water exit in accelerated motion, the cavity on the shoulder collpases from on side all the time and the cavity on the bottom is separated into two cavities under the pressure of the water and they collpases respectively. In decelerated motion, the cavity on the shoulder collapses from two sides, and the cavity on the bottom is ringlike, of which the volume will rebound slightly.