펌프 흡수정 내 보텍스 거동에 관한 연구

Abstract

Water absorbed towards the inlet of the pipe creates unsteadiness. If there are design problems in the pump suction pipe of water tank, resulting in vortex and swirl generation inside the tank. There are two vortex types. Free surface vortex and sub-merged vortex. Free surface vortex starts from free surface, then generates the air column and air drop near inlet. On the other hand, sub-merged vortex is due to swirl generation from the side wall of water tank or the bottom as far as the inlet of pump. Both water and air absorbed together creates vortex. Not only the pumping efficiency is decreased, but also produces noise and oscillation. Changes of pump breakdown are possible, because of friction between air drop and blade. Hence, it is necessary to test the pump before installation, in order to confirm whether the station of fluid flow inside the water tank affects the performance or not, due to the long cycle process and also the high cost involved. The purpose of this study is to compare the multi-phase and single-phase model and to evaluate the difference between them. Also steady and unsteady simulations are conducted to verify the differences in results according to the analysis conditions. A pump sump test model is calculated using CFD and the following points are observed. 1)The location and the behavior of the free-surface and submerged vortex 2) Free-surface vortex in the multi- phase and single-phase method. A practical model and TSJ Standard S002:2005 are used for numerical computation for the model of this study. Numerical results show that the unsteady multiphase model is the best to implement the creation and dissipation of the vortex along time. The location and the shape is similar for all cases but only case 3 and 6 represent the concrete location and change of the submerged vortex along the time. In accordance with this result, it is recommended that the multiphase unsteady flow is suitable to study the submerged vortex in pump sump model.