와류방지장치(AVD)를 설치한 펌프장 흡수정의 유동특성 및 사류펌프의 성능해석에 관한 연구

Abstract

The head-capacity curves of pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no closed walls or floors and with no stray currents. Therefore, the flow into the pump intake has no vortices or swirling. However, pump station designers relying on these curves to define the operating conditions for the selected pump sometimes experience reductions in capacity and efficiency, as well as an increase of vibration and additional noise, which are caused by free air mixed with the pump inlet flow. Therefore, sump model testing is necessary in order to examine the flow structure around intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail. A multi-intake pump sump model with 7 pump intakes and a single-intake pump sump model are adopted for the investigation of submerged vortex, while a sump model with 10 pump intakes is adopted for free-surface vortex. Furthermore, in the sump model for the submerged vortex, the effectiveness of an anti vortex device(AVD) for the suppression of the vortex occurrence in a single and multi intake pump sump model has been examined by experiment and numerical methods. In the sump model for free-surface vortex, Under operating conditions of the pump, the free-surface vortex occurrence is examined together with there effectiveness of anti-free-surface vortex device in the sump model of pump station. For the pump performance characteristics, an impeller and diffuser for a mixed flow pump was designed, and a fluid analysis of the mixed flow pump was carried out. An efficiency of the flow mixed pump was studied about non-uniform approach flow at bell-mouth with and without the AVD. An uni-direction fluid-structure interaction(oneway FSI) analysis of the impeller and diffuser was implemented.

In the submerged vortex study, the results show that highest value of flow uniformity is found at the inlet of pump intakes in the multi-intake pump sump. Therefore, when the pump station is designed, the flow patterns at the upstream region of pump intake inlet in the forebay diffusing area should be considered in detail because of the unbalanced flow at the channel inlet region gives considerable influence on the vortex occurrence around bell-mouth. Strong submerged vorticies can be successfully suppressed by installing an AVD on the bottom of pump intake channel just below the bell-mouth.

In the free surface vortex study, depending on operating pumps of various combinations, the free surface vortex was occurred at different position. However, The AVD was able to suppress the free surface vorticies. The efficiency of the pump installed within the bell-mouth in the sump is reduced by the flow characteristics of around intakes.

In the mixed flow pump performance study, the efficiency without and with sump model was 90.9% and 89% respectively at the design flow rate. The difference in efficiency between with and without the cavitation model and is 4.2%. As the approach flow condition increases in uniformity of flow to bell-mouth, the efficiency for the mixed flow pump also was increased. As the structure analysis results show that the stress is lower than the allowable stress.