Research On Secondary Side Flow Field Characteristics Of Steam Generator And Flow-induced Vibration Of Tubes

It is of great significance for the design guidance and safe operation of the steam generator to study the characteristics of fluid including velocity,temperature,and vapor fraction in the secondary side flow field of the steam generator and to obtain the turbulence excitation force and other data used for further study on the flow-induced vibration and fretting wear of tube.Firstly,based on the “unit pipe” model and combined with the porous media model,an embedded mixing model was proposed to study velocity,temperature,and vapor fraction in the secondary side flow field.The results show that the water in the secondary side of the steam generator boils at a constant temperature.The maximum vapor fraction of the hot side and cold side is 0.97 and 0.73 respectively,showing a significant difference.Tubes outside the tube bundle have a higher risk of fluid-induced vibration failure,especially near the inlet and the U-bend region.The detailed flow field data along tubes at dangerous position were obtained by using embedded mixed model,which provides basic data for dynamic analysis of tubes.Secondly,the influence of operation parameters such as feed water supply ratio and total power were studied.As the water supply ratio changed from 1:1 to 1:4,the initial height of boiling on the hot side rose by 0.3m and the cold side decreased by about 1m,but it had little influence on the U-bend region.For 30% power,the initial height of boiling on both sides rose by 4m and 3m respectively,but produced less steam.For 120% power,the difference of vapor fraction on both sides enlarged.In actual operation,the power should be appropriately reduced and water supply on the hot side should be increased to improve the flow condition and two-phase distribution.Finally,the beam element and the shell element were used to simulate the tube and the anti-vibration bar respectively,then the data of transverse velocity and fluid density were converted into dynamic turbulent force by using the power spectral density and loaded onto the tube.The nonlinear dynamic analyses were carried out by explicit dynamics.The results show that the effect of the anti-vibration bar on the tube is similar to simple support.The amplitude of the tube on the outside of the tube bundle is larger than that on the inside of the tube bundle,and as the radius of the bend decreases,the difference between the two sides decreases.Tubes on the hot side are more susceptible to fretting wear.Five tubes with high failure risk were selected for fretting wear analysis.The maximum wear depth is 35.32% of the tube wall thickness and does not exceed the maximum allowable wear depth of 40% of the tube wall thickness.The change of wear depth was simulated by adjusting the gap of anti-vibration bar.The results show that the change of amplitude in the In-plane direction is not obvious.The local maximum wear power is self-limited,and the wear depth gradually slows down.The results can provide reference for the design and operation of steam generator and the life prediction of tube bundle.