흡수정 모델의 유동해석과 와류제거장치(AVD) 설계에 관한 연구

Abstract

Worldwide, an increasing demand of electricity leads to a many number of constructions of power plant. In power plant producing huge amount of electricity, a large-scale pump with high flow rate is installed. Although a performance of the large-scale pump is determined by the stage of design and manufacture, the Pump intake design is the most significant consideration for pump performance and life.

As a crucial part of the pumping station, sump is designed to provide uniform. To attain the uniform flow in the sump needs a civil construction of large scale. By contrast, compact design of pumping station is main concern for global construction companies. However, the compact pump intake design without sump model test can result in undesired flow conditions. For instance, a flow passing through an insufficient length of sump arrives at pump entrance as non-uniform flow, and it causes deleterious effects on pump such as vibration and noise. In addition, a vortex due to inappropriate design of sump can leads to cavitation nearby the intake pipe which not only impacts on the impeller but also generates vibration. The decline of pump performance and high maintenance can be acquired due to these undesired flow behavior. Thus, to predict the flow behavior the model test of sump is conducted.

The sump model test is commonly processed during the new or the period of pump replacement. Through the model test an optimized AVD (Anti-Vortex Device) for sump wasinvestigated and designed, and its performance was assessed. Currently, numerous needs of sump model test has been requested due to the rapid increase of pump demands globally, and to fulfill the demands the development of AVD technology is emphasized.

In this study, the comparative analysis of flow behavior around intake entrance by PIV method, which visualizing the fluid field, and ANSYS CFD tool was conducted. A swirl angle of swirl meter for the sump model test was investigated at different types and locations. Design parameters of AVD were determined based on various types of sump, and it was verified through the 30 cases of sump model tests with different geometries. In addition, the combination of sump model and AVD is suggested.

A swirl angle varies by 10% with the amount of flow rate of sump, and the averaged range of swirl angle by ANSI/HI 9.8 standard guideline is dictated from 0.5 to 5 degree. The maximum error of swirl angle was 8% according to materials, thickness and weight of swirl meter, and the range of 0.4 to 5 degree is the averaged range of swirl angle by ANSI/HI 9.8. In constant flow rate, the swirl angle according to different locations of swirl meter at 4d was 5% lower than at 0.5d, and it has an error by 0.25 degree at the averaged 5 degrees of swirl angle. From numerical analysis of sump by ANSYS CFD the maximum gap of swirl angle was 3.5% compared to experimental result. When eliminating submerged vortices and with bottom AVD the result of swirl angle was decreased as 0 ~10%, and also the angle was decreased as 20% when surface vortices were removed. The reduction of swirl inside the intake pipe was obtained by the installation of AVD.

The relation formula according to design parameters of AVD such as diameter and cross-sectional area of sump, distance between intake entrance and the bottom, and distance between the center of intake pipe and the back wall is illustrated. A stabilization of the flow was verified by that submerged and free surface vortices were removed by the combination of AVD manufactured with the design method, Curtain wall and distributors.