Dynamic hydraulic characteristics of a prototype ball valve during closing process analysed by 3D CFD method

Abstract

During the runaway process of high-head turbine-generator units due to wicket gate failure, the ball valve should be closed promptly to prevent accidents, and the dynamic hydraulic characteristics during the closing process should be studied. In this paper, the flows through a prototype ball valve are simulated by the latest 3D CFD method. First, the steady flows in different openings are calculated, and we find that the headloss coefficients agree well with experimental results. Then, the water hammer led by linear closing of the ball valve is simulated by both 3D CFD and 1D Method of Characteristic (MOC), and the reasonable agreements further validate feasibility of the 3D CFD method. After that, we investigate the evolution laws of flow patterns, pressure and forces around the valve, and find that the pressure variations before, within and behind the valve differ greatly. Besides, the unstable flow fields within the valve are essential causes of pressure and force fluctuations, bringing potential danger to the safety of ball valve operation. This research provides basic information for studying ball valve vibration and its impact on the turbine and hydraulic system.