Numerical Simulation Of Flow Characteristics In Mid-pressure Valve Of AP1000 Nuclear Steam Turbine

The inlet valve is a steam’s regulating equipment for the steam turbine. Its performance determines the economy and safety of the steam turbine’s operation. The steam parameters in nuclear power plant are low and the mass flow of the steam is large. The steam’s volume flow in mid-pressure pipe is larger than that in high-pressure pipe. The torque generated by the steam is large, so the jamming faults often occur in the process of valve’s action. Main steam in nuclear power plant is saturated steam and wet steam flow may occur in mid-pressure steam pipe, which makes the unit’s operating efficiency lower. So it is necessary to study the steam’s flow in mid-pressure valve of nuclear steam turbine.In this paper,the software FLUENT is used to make the numerical simulations for the flow characteristics in mid-pressure butterfly valve of AP1000 nuclear steam turbine. The velocity fields and pressure fields are respectively analyzed under control valve’s different openings. The pressure loss and pneumatic torques are discussed.Make researches for the flow fields of wet steam’s two-phase flow,pressure loss,and the pneumatic torques with the change of the control valve’s opening. The results obtained are compared with the simulation results of simple-phase flow. Simulation results show that:When the main valve and control valve are fully opened, the pressure and velocity distributions in valve are symmetrical. When the valve’s opening reduced to60° or 30°, the steam velocity’s variation around the valve disk is remarkable.Because of the valve disk’s barrier, the vortex is formed at the back of disk. With control valve’s opening decreasing, the proportion of pressure loss in control valve increases. When control valve’s opening is approximately less than 75°, the pressure loss in control valve is larger than that in main valve. When the control valve’s opening is roundly 30°, the pressure loss in main valve is negligible relative to the pressure loss in control valve.In the process of control valve’s opening’s increase, the pneumatic torque increases gradually and peak value occurs when the opening of the control valve is around 30°,after which pneumatic torque decreases gradually with the increase of the opening. Wet Steam’s flow fields are similar to the single-phase flow’s fields in the valve. There is a relative slipping velocity between the steam and water droplets in thewet steam, causing a lot of friction loss. So two-phase flow’s maximum flow velocity are lower than single-phase flow’s in the valve when control valve’s opening is at 10°,40° or 90°. At the same control valve’s opening, the two-phase flow’s pressure loss is nearly double what it is in the single-phase flow. At three openings of 10°, 40°and 90°,the two-phase flow’s pressure loss is twice over that of single-phase flow when moisture content rises to 2% from 0.5%. So the moisture content in the steam severely affects the economy of plant operation.Pneumatic torque’s variation in two-phase flow is similar to that in single-phase flow. At the same control valve’s opening, the pneumatic torques in two-phase flow have different degrees of increase compared with the single-phase flow. When the control valve’s opening is 30°, pneumatic torque’s difference between two-phase flow and single-phase flow is maximum. Therefore, jamming fault is more likely to occur in wet steam flow.