Numerical Simulation Of Dynamic Characteristics In Mid-pressure Regulating Valve Of CPR1000 Nuclear Steam Turbine

The mid-pressure regulating valve is the key part of connecting high pressure cylinder and medium pressure cylinder,its performance determines the economy and safety of the steam turbine's operation.For 1000 MW nuclear steam turbine,the steam flow in mid-pressure cylinder inlet pipe is large,and the size of mid-pressure regulating valve is also great,so the valve plate and the valve stem will bear great force and torque,valve in the closed process prone to jamming fault,which will seriously affect the safety and economy of the unit.It is very necessary to study the dynamic characteristics in the closed process of mid-pressure regulating valve.Take the mid-pressure regulating valve of a 1000 MW nuclear steam turbine as an objective.Firstly,Take dry steam as medium,and its unsteady numerical simulation of the flow field and aerodynamic characteristics of the valve in the valve closing process is carried out by using Fluent software and sliding grid technology.The change regulation with the time variation of the velocity field distribution,the pressure field distribution,the pressure loss and the aerodynamic torque are obtained.According to the change regulation of the aerodynamic torque,the reason of the valve jam in the closing process is discussed.Secondly,take the wet steam as medium,unsteady numerical simulation is carried out by using mixture model.The influence of humidity and water droplet diameter on the flow field and the aerodynamic torque are discussed.The calculated results show:In the valve closing process,The non uniformity of the velocity field distribution and the pressure field distribution first enhanced and then weakened with the time,in t=0.3s,that is,when the valve opening is 40%,the most obvious.The change regulation of aerodynamic torque is also the trend of first increased and then decreased,and the maximum value is reached at t=0.3s.The change regulation of aerodynamic torque leads to the resultant torque of the valve has been changed,at a certain moment,if the spring torque does not match the actual need to close the valve torque,it will lead to the jamming fault of the valve.Wet steam and dry steam velocity field distribution is basically the same,but the maximum velocity of dry steam is lager than the wet steam in different time.The effect of steam water content on pressure loss and aerodynamic moment is very large.The higherthe volume fraction,the greater the pressure loss and aerodynamic moment of the valve.But in a certain range,the influence of droplet diameter on the pressure loss and aerodynamic moment is not obvious.