This study investigates the effect of orifice-pipe misalignment on flow characteristics and pressure hunting in a pilot valve using transient CFD analysis. Four models were created with a circular orifice (1 mm radius, 1 mm length) placed at offsets of 0.25 mm, 0.5 mm, 0.75 mm, and 1 mm from the pipe centerline (pipe diameter: 4 mm). Simulations were performed in ANSYS CFX with a 6.8 m/s inlet velocity and 3.2 bar outlet static pressure. A High Resolution advection scheme and Second-order Backward Euler time integration were used. Results showed that greater eccentricity led to more severe pressure hunting, with the 0.75 mm model showing a maximum of 7.61%. In contrast, the 1 mm model stabilized quickly after initial fluctuations. Velocity and streamline analyses also confirmed that asymmetry promotes swirl and backflow. These findings highlight the importance of orifice alignment in achieving stable valve performance.

Abstract
1. 서 론
2. 전산유동해석
    2.1 해석 모 델
    2.2 Mesh
    2.3 Methodology
    2.4 Results and Discussion
3. 결 론
References

• 곽효서(Assistant professor, Mechanical Engineering Major, Dong-Eui University) | Hyo-seo Kwak Corresponding author