Influence Of Gap Flow On Unsteady Flow In Reactor Coolant Pump And Rotor Dynamic Characteristics

The reactor coolant pump is the main power transmission equipment in the nuclear reaction system,and its efficient and stable operation is an important guarantee for the safety of nuclear power.As one of the important components of the reactor coolant pump,the impeller mouth ring seal interacts with the main flow of the pump inlet,resulting in unstable transient flow in the pump,which poses a serious threat to the safe and reliable operation of the reactor coolant pump.At present,most of the research on orifice-ring gap flow is based on centrifugal pumps,and there are few related studies on gap flow based on reactor coolant pumps.Therefore,by comparing different port ring seal structures,this paper explores the effect of port ring gap flow on the performance and rotor dynamics of the reactor coolant pump,which is of great significance for the structural optimization and stable operation of the reactor coolant pump.Firstly,for the structure with or without orifice ring seal,this paper adopts numerical simulation method to study the influence mechanism of the gap flow of the orifice ring seal on the internal and external characteristics of the reactor coolant pump,and reveals the distribution law of stress and strain of the impeller structure with or without the orifice ring seal.The research shows that when the mouth ring seal is considered,the head of the pump and the impeller are reduced by 1.65% and 1.23%respectively at the design operating point,and the efficiency is reduced by 2.43% and2.56%,and the drop is even greater under the large flow conditions.The gap flow of the orifice ring mainly affects the axial velocity of the fluid at the inlet of the impeller,which causes the occurrence of unstable flow in the pump,and finally affects the distribution of the pressure and velocity field in the pump.Among them,when the sealing of the mouth ring is considered,the pressure at the inlet of the impeller and the middle position of the guide vane flow channel has the most obvious change,which is reduced by 22.07% and 19.73%,respectively.The maximum deformation and the maximum equivalent stress position of the impeller structure change,the modal frequency decreases,and the stress and strain decrease with the phase change.Secondly,the internal and external characteristics and structural dynamic characteristics of the core main pump with different port ring seal structures are studied.The influence mechanism of the change of the sealing structure of the mouth ring on the stability of the reactor coolant pump is analyzed,and the influence mechanism of the sealing structure on the deformation and stress distribution of the flow passage parts is clarified.The research shows that when the plane seal,labyrinth seal and screw seal are used,the leakage of the reactor coolant pump port ring decreases in turn,and the lift,efficiency and radial force increase in turn.Under the design conditions,compared with the plane seal,the leakage of the labyrinth seal and the spiral seal port ring is reduced by 13.9% and 48.3%,the lift is increased by 0.48% and 1.12%,and the efficiency is increased by 0.36% and 1.33%.The frequency amplitudes increased by12.63% and 16.37%,respectively.The flow in the front cavity of the pump is obviously affected by the structural change of the mouth ring,and the circumferential inhomogeneity of the pressure distribution on the rotating wall of the front cavity of the screw seal pump is the largest,resulting in the difference in the radial force of the impeller.The maximum deformation and maximum equivalent stress distribution of the impeller with different mouth ring structures remain unchanged,but the magnitudes are different.Under the same phase,the deformation values of the plane seal,labyrinth seal and spiral seal increase in turn,and the equivalent stress value and impeller modal frequency decreasing in turn.It shows that the change of the mouth ring structure has an important influence on the stable operation of the reactor coolant pump.Finally,further using the rotor dynamics theory and finite element calculation method,the motion model of the seal-rotor coupling system is established,and the influence of the change of the mouth ring structure on the rotor stability is analyzed.The results show that the change of the mouth ring structure changes the excitation force of the mouth ring seal,and then affects the dynamic parameters of the mouth ring seal.The main stiffness coefficient of the labyrinth seal structure is the smallest,and the main stiffness coefficient of the spiral seal structure is the largest,which is 49.4% higher than that of the labyrinth seal.The modal vibration patterns calculated by different ring structures are consistent.Compared with the fluid-structure coupling effect,the gap circulation effect has a greater impact on the critical speed of the rotor,and has the most obvious impact on the first-order critical speed.Compared with the "dry" rotor The firstorder critical speed of the rotor is increased by 24.8%,20.7%,and 26.7%,respectively,under the effect of the gap circulation effect of the plane seal,labyrinth seal,and spiral seal.From the above results,it can be concluded that the gap flow of the mouth ring seal has an important influence on the internal and external characteristics and structural dynamic response of the reactor coolant pump,and the effect of the gap flow cannot be ignored in the structural optimization and numerical calculation of the reactor coolant pump.The research results will provide important reference value for the stable operation of reactor coolant pump and the evaluation of structural reliability design.