Study On Internal Flow And Dynamic Characteristics Of Nuclear Main Pump Based On Fluid-solid Coupling

Vibration is inevitable in the operation of a nuclear main pump.Vibration will not only affect the stability of its operation,but also affect its safety as well as shorten it`s life.Therefore,reducing vibration can not only improve the reliability of nuclear power unit operation,but also reduce the incidence of major accidents in nuclear power plants and avoid the loss of national property,which has important economic value and social significance.The unstable flow inside the rotor structure of the nuclear main pump is an important reason for the vibration of the nuclear main pump unit.Therefore,based on the calculation and test results,the influence of rotor cantilever ratio,rotor clearance and guide vane circumferential placement position on the flow and dynamic characteristics of a nuclear main pump was studied in this paper,which provides effective help for the follow-up study of the nuclear main pump.The main contents are as follows:1.The influence of rotor cantilever ratio on the dynamic characteristics of a nuclear main pumpIn order to investigate the influence of cantilever ratios of rotor on the hydraulic vibration of the nuclear main pump,25 model schemes for the CAP1400 nuclear main pump were designed by altering the cantilever ratio of the pump shaft under the condition that other geometric parameters determined.Based on Reynolds time averaged N-S equations and RNG k-? turbulence model in multiple reference frames,full three-dimensional numerical calculation was carried out for reduced-scale models of nuclear main pump with solid coupling method,the variation law of stress and strain of the impeller blade of the nuclear main pump was analyzed under the different cantilever ratios and working conditions.The rotor dynamics characteristics of the nuclear main pump with different cantilever ratios were investigated under the conditions with pre-stress and without pre-stress.The results reveal that when the cantilever is of fixed length,the stress,strain of the impeller blade and the first 6 order natural frequencies of the rotor have little correlation with the cantilever ratio,while having great correlation with the working condition.The maximal deformation of the impeller blade of the nuclear main pump increases with the increase of the length of the cantilever,whereas not changing with the increase in cantilever ratio.The maximal stress does not change with the change of the cantilever length and the cantilever ratio.The fluid solid interaction can reduce the natural frequency of the rotor system,and the magnitude of reduction decreases with the order number increasing.2.The influence of rotor clearance ratio on internal flow and dynamic characteristics of nuclear main pumpIn order to study the influence of stator and rotor cascade clearance on performance and rotor dynamic characteristics of reactor coolant pump,the CAP1400 reactor coolant pump is taken as the research object.Based on numerical calculation and experimental results,the influence of stator and rotor cascade clearance ratio on performance of reactor coolant pump and stress,strain and modal of the rotor are analyzed by unidirectional fluid-solid coupling method.The results show that the influence of rotor clearance ratio on the external characteristics of the nuclear main pump and its impeller is related to the working conditions,and varies with the working conditions.In terms of hydraulic loss of guide vanes and turbulent kinetic energy distribution of main flow passages,the clearance ratio has less influence on hydraulic loss and turbulent kinetic energy distribution in guide vanes under design conditions.In large flow conditions,clearance ratio has greater influence on the distribution of guide vane loss and high turbulent kinetic energy region,and the distribution area of guide vane loss and high turbulent kinetic energy region decreases monotonously with the increase of clearance ratio.The ratio has a great influence on the turbulent kinetic energy value and distribution,and the influence on the guide vane loss is first reduced and then increased,and there is an optimal value.As far as the dynamic characteristics of the rotor are concerned,the clearance ratio has a greater influence on the maximum equivalent stress on the back of the impeller blade,and the influence on the working face is smaller.The maximum equivalent stress on the back of the blade is about three times as much as that on the working face,but it has less influence on the first six natural frequencies of the rotor.The first three orders are the integral vibration of the impeller,and the last three orders are the integral vibration of the impeller and the lower flywheel.Bend and twist.This study can provide reference for the design and structural optimization of nuclear main pump.3.The influence of guide vane circumferential placement position on internal flow and dynamic characteristics of nuclear main pumpIn order to study the influence of the circumferential placement position of the guide vane on the flow field and stress-strain of nuclear main pump,the CAP1400 reactor coolant pump is taken as the research object.Based on numerical calculation and experimental results,the influence of circumferential placement position of the guide vane on performance of reactor coolant pump and stress-strain of guide vanes are analyzed by unidirectional fluid-solid coupling method.The results show that the physical model and calculation method used in the study can accurately reflect the influence of the circumferential placement position of the guide vane on the nuclear main pump,and the error not exceeding 0.22%.Under the design condition,its position has a great influence on the nuclear main pump efficiency value,suction surface of guide vane blade and the maximum equivalent stress on the rear cover plate.However,it has a little influence on the head value,pressure surface of guide vane blade and the maximum equivalent stress on the front cover plate,and when the center line of the outlet diffuser tube of the pressurized water chamber is located at the center of the outlet of flow channel of guide vane,it is an optimal guide vane circumferential placement position,which can reduce the hydraulic loss of half of the pressurized water chamber.Finally,it is found that the interse ction of the exit edge of the vane blade and the front and rear cover is a high stress concentration area,and the exit edge of the guide vane blade and its intersection with the front cover are most susceptible to strength damage areas.This study provides a reference for nuclear main pump installation,shock absorption design and structural optimization.