| Nuclear power is one of the most promising clean energy and an indispensable part of the new energy supply system.Main feed water regulating valve(MFWRV)is the key equipment in nuclear power plant(NPP),which is used to control the water level in steam generator by adjusting the flow rate of feed water in the second loop.However,MFWRV generally presents some problems,such as low regulation accuracy,poor structural reliability,and frequent occurrence of cavitation in switching condition,which pose serious harm to the safety and reliability of NPP.In-depth study of the internal flow and structural mechanics characteristics of MFWRV is helpful to solve the above problems,and also to perfect the design theory system of MFWRV and similar nuclear power valves.Supported by National Natural Science Foundation of China through No.51875514 and No.51805470,and Key Research and Development Program of Zhejiang Province through No.2021C01021,this dissertation studied flow characteristics,cavitation characteristics,and structural mechanics characteristics of MFWRV,respectively.The main contents and achievements are as follows:(1)Numerical research model for flow characteristics,cavitation characteristics,and structural mechanics characteristics of MFWRV were established,respectively.By simplifying the pressure boundary consisting of valve body and valve cover,the flow test device for throttling components of MFWRV was designed and built.The number of throttling windows and the flow area were taken as experimental variables to carry out the flow experiment for throttling components of MFWRV.At the same time,the flow experiment for the whole valve was carried out under typical valve openings.The accuracy and validity of the numerical research model of MFWRV are verified by the experiment.(2)Effects of the valve opening and the throttling window shape on the overall flow evaluation index,the flow field inside valve and the force characteristics of valve core were studied.The results show that with the shape of the throttling window changing from inverted funnel to positive funnel,the maximum axial and lateral hydraulic forces of valve core decrease first and then increase,while the maximum liquid torque of valve core increases gradually.Meanwhile,the inherent valve characteristic curve realizes the continuous variation from equal percentage characteristic to linear characteristic and then to fast opening characteristic.According to this,a shape coefficient of throttling window and a prediction formula of valve inherent characteristics based on shape coefficient of throttling window were proposed.The existence and change of vortex in valve body is the internal reason that the slope of inherent characteristic curve of valve drops suddenly when the valve opening exceeds 75%.(3)Effects of working condition parameters and structural parameters on the overall evaluation index and the characteristics of cavitation flow field inside MFWRV were studied.The results show that under the same conditions,the steam phase volume inside the valve could be significantly reduced by changing the flow direction of the feed water from forward flow to reverse flow.At the working condition corresponding to the maximum vapor phase volume,the ability of MFWRV to restrain cavitation increases with the increase of the number of throttle windows.Under different flow directions,number of throttling windows and pressure drop across the valve,the deviation of the resistance coefficient under the condition of two-phase flow relative to that under the same condition of single-phase flow could be expressed by the same function relation.Based on this,the calculation method of resistance coefficient of MFWRV with cavitation influence under switching condition was put forward.(4)The calculate modal characteristics and structural mechanics characteristics of MFWRV under different valve openings and load combinations are studied.The results show that the prestress effect makes the calculated natural frequencies of MFWRV decrease slightly.When the valve opening and the load combination change,the point of maximum swing(or oscillation)in different modes of vibration is always located above the valve cover.The loading form of the flow field has no obvious effect on the maximum stress intensity of the pressure boundary.Compared with the uniform flow field,the non-uniform flow field will increase the maximum stress intensity of the whole valve within the whole valve opening range.In the whole valve opening range,the increase rate of the maximum stress intensity of MFWRV under the action of non-uniform flow field relative to it under uniform flow field is calculated.Based on this,the reduction coefficient of the maximum allowable stress of MFWRV by non-uniform flow field is proposed. |
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