329 Dynamic analysis of three-dimensional flow in the opening process of a single-disc butterfly valve L Wang, X G Song, and Y C Park ∗ Department of Mechanical Engineering, Dong-A University, Busan, Republic of Korea The manuscript was received on 15 April 2009 and was accepted after revision for publication on 16 July 2009. DOI: 10.1243/09544062JMES1679 Abstract: A numerical dynamic analysis is carried out to simulate a three-dimensional flow and to study the performance of a single-disc butterfly valve with a diameter of 1.35 m in the opening process. The unsteady fluid flow during the opening process is studied by using the moving grid technique. The turbulent separated flow is also studied to understand the unsteady flow better through velocity distributions and pressure distributions on the mid-symmetric plane. The formation of vortexes is also discussed. Then the characteristics of butterfly valves such as the flow coefficient, the dynamic torque coefficient, and the drag coefficient are studied. The curves of these characteristics corresponding with the variational valve opening angle are obtained to investigate the performance of the single-disc butterfly valve. Keywords: single-disc butterfly valve, moving grids, dynamic analysis, flow coefficient, dynamic torque coefficient, drag coefficient 1 INTRODUCTION Single-disc butterfly valves in large diameter are widely used to control the flow of gas, oil, or water in transport system. They consist of three main com- ponents: the circular disc, the shaft, and the valve body. They have advantages such as light weight and a relatively high flow capacity in controlling fluid flow because of the small resistance of discs in the fully opened position. In the last two decades, most researches investigated the performance of butterfly valves in two dimen- sions rather than in three dimensions. This has shown that, in two-dimensional (2D) analyses, the difference between the computed flow coefficients and those of the published valves increases as the valve opening increases, although the trend of changes of the flow coefficients between the two results was agreeable [1]. The main reason could be that a 2D flow model was inaccurate around the valve plane for the flows. Therefore, in 1996, Huang and Kim [2] conducted a numerical analysis with a 3D mathematical model to ∗ Corresponding author: Department of Mechanical Engineering, Dong-A University, #840 Hadan 2 dong, Saha-gu, Busan 604714, Republic of Korea. email: parkyc67@dau.ac.kr investigate the incompressible flow of butterfly valves using FLUENT TM . Usually, the dynamic torque coefficient and flow coefficient are the most important parameters of but- terfly valves for on–off or controlling applications. Recently, most researches studied the performance of butterfly valve through them. In 1999, Solliec and Danbon [3] investigated the aerodynamic torque on a butterfly valve, and discussed different definitions of dynamic torque coefficient. In 2006, Park and Chung [4] studied the hydrodynamic torque of a butterfly valve through the free-streamline theory by compar- ing the 2D and 3D torque coefficients between the previous theoretical model and a developed model. Also in 2006, Leutwyler and Dalton [5] conducted a computational study of disc to accurately obtain flow characteristics of the butterfly valve using FLU- ENT. In 2007, Song and Park [6] investigated the flow coefficient and hydrodynamic torque coefficient of a single-disc butterfly valve using CFX TM . However, most researchers studied unsteady flow through butterfly valves using static analysis rather than dynamic analysis. To obtain better results in this study, a dynamic analysis is conducted with mov- ing grids which has a high requirement of mesh quality. Actually, it is very essential to generate a high quality computational grid for valve geometry, which usually takes two-thirds of the time of any CFD JMES1679 Proc. IMechE Vol. 224 Part C: J. Mechanical Engineering Science