펌프 흡입정 주위에서 발생하는 와류제어에 관한 연구

Abstract

Pump intake is a civil engineering structure which includes filtration equipment, rectifying and suction devices in order to draw supply water from the ground, river and sea using pumps. It is mainly used in facilities such as industrial power plants, which requires a large amount of industrial water that needs to be fed continuously. Therefore, it is vital to have an optimum hydrodynamic design in order to ensure the performance of a suction pump. Earlier research activities on pump intake were mainly carried out using single-phase model, in which the air intake to the pump, vortex and other phenomena were not addressed. Hence, the purpose of this study is to investigate the characteristics of the internal flow of a pump intake through the multi-phase flow model. Using the multi-phase numerical analysis model and experiments, the characteristics of vortex - which interferes in the stable operation of the structure – is studied. With the help of the multiphase numerical analysis technique, the vortex behavior on the free surface can be visualized both quantitatively and qualitatively. To control the vortex, an Anti Vortex Device (AVD) is installed near the suction pipe. The effectiveness of the AVD is tested experimentally by applying the law of similarity; the experimental results are compared with the numerical analysis. The multiphase flow analysis is calculated from ratio of each (water and air) volume in space. The free surface vortex could be visualized at the interface intersection of the space, where the ratio of air to water volume is 1%:99%; also, it was found that the shape and location of the vortex matches well in both the experimental and computational results. Also, when the location of a suction pipe changes its position, the motion of the free surface vortex repeats for a period of 8 seconds cycle. The amount of air entering into the intake pipe is analyzed numerically to study the characteristics of the vortex, by taking the flow rate of water and height of free surface as the variables. According to the results, it has been confirmed that the free surface vortex occurs in every cases (nine cases), except for three cases with highest free surface and with the minimum flow rate of water. The case with the roughest operating condition has shown at least 8.8 times of the amount of air suction than the cases with other conditions. Also the amount of air suction rises more by lowering the height of the free surface, than by increasing the flow rate of water. Thus, it is thought that the control of the height of free surface rather than the suction flow rate is more necessary to reduce the loss of the pump power by the free surface vortex. In the experiment using the down scale model where the law of similarity has been applied, the study to control the vortex with the AVD of the optimum shapes, which had been obtained through the numerical analysis, has been carried out. An ink dye was used for visualizing the trace of the behavior of vortex occurring inside of the experiment model. The results have shown that the vortex can be controlled by means of an AVD, and the improved E-type AVD has superior vortex control effect than the AVD made with HI Standard. The superiority of the E-type AVD also has been verified with the quantitative data via the measurement of swirl angle and inlet velocity of water at the intake pipe.