| The reactor coolant pump(RCP)is the key equipment of pressurized water reactor(PWR)nuclear power plants(NPPs).The operation reliability of RCP is directly related to the safety of NPPs.The internal unsteady flow and flow-induced vibration problems are particularly concerned and important for the RCP which requires extremely high reliability.Studying the mechanisms of internal unsteady flow,thus proposing the hydraulic excitation suppression approaches,is of great value to improving the stability and reliability of the RCP.Based on the verified unsteady CFD methods and two characteristic parameters of flow field proposed to represent the rotor-stator interaction(RSI),in this thesis,the characteristics of the internal unsteady flow,RSI and excitation force,and the effects of the static hydraulic components and impeller structures,for the axial-flow RCP with the same hydraulic structure of that in “HPR-1000”,were systematically studied.And then,the strategy and approaches for the unsteady flow optimization and the hydraulic excitation suppression were proposed.The main contents of this thesis include the following aspects:(1)The CFD methods for the internal flow of axial-flow RCP were studied,and the CFD results were validated by test data.Through the comparision and analyses on the CFD results based on different turbulence models and different combinations of boundary conditions,the modeling and numerical methods for the steady and unsteady simulation were optimized and validated.The results show that: the steady simulation results based on Realizable k-? model are in good agreement with the test data;and the unsteady CFD method based on the reasonable and realistic boundary condition combination of “pressure inlet & mass flow rate outlet” has higher accuracy on the prediction of the pressure pulsation at blade passing frequency(BPF)related to the RSI,at both the suction and discharge sides of RCP.(2)Two characteristic parameters for describing the internal unsteady flow field of axialflow RCP were proposed.That was the Local Euler Head(LEH)pulsation at both sides of the impeller,and the flow variables pulsation in the rotating frame of impeller,which were respectively used to analyze the disturbing action of rotor(impeller)and the reaction of stator(static hydraulic components)in the RSI problem.The specific definition and extraction approaches of these two characteristic parameters were also given.(3)The unsteady flow and exciting force characteristics of the axial-flow RCP were studied.The mechanism of the RSI was analyzed based on the LEH pulsation at both sides of impeller and the flow variables pulsation in the rotating frame of impeller,and the strategy for unsteady flow optimization and hydraulic excitation suppression was proposed.The results show that: the RSI is the primary excitation source for the internal unsteady flow and hydraulic excitation of the axial-flow RCP;the RSI generally exists in the rotating impeller and all static componets that cause circumferential uneven flow patterns upstream and downstream of the impeller;and the circumferential uniformity of the flow fields in rotating frame and fixed frame has important impacts on the RSI;improving the circumferential uniformity of the flow fields and energy distribution in both impeller and static components,can effectively reduce the RSI,and thereby reduce the pulsation of unsteady flow and suppress the hydraulic excitation.(4)The effects of static hydraulic components on the unsteady flow of axial-flow RCP were studied,and the corresponding improvement approaches for hydraulic excitation suppression were proposed.The results show that: the suction and discharge conditions of the RCP have significant effects on the exciting force;the radial fluid force pulsation of impeller is significantly reduced without the suction elbow,and the double-discharge RCP casing also has suppression effect on the hydraulic excitation.For the structure with suction elbow,the adverse effects can be effectively controlled by increasing the distance between the elbow and the impeller of pump body;and when the distance between suction elbow and impeller is increased to more than 2.4times the suction diameter,the radial fluid force pulsation of impeller is significantly reduced.The match between the number of impeller blades and diffuser vanes significantly affects the excitation force;an appropriate increase in the number of diffuser vanes is beneficial to the reduction of the radial fluid force pulsation of impeller and the hydraulic excitation suppression.(5)For the impeller,the design methods for hydraulic excitation suppression were proposed on basis of the optimation of its blade stacking condition and meridional shape.The results show that: the stacking condition that makes the trailing edge(TE)of impeller blade and the leading edge(LE)of diffuser vane tilted to each other,reduces the the RSI between the impeller and diffuser,and the hydraulic excitation force significantly decreases;the larger the axial angle between the TE of impeller blade and the LE of diffuser vane,leads to the lower the radial fluid force pulsation of the impeller.By retracting the blade LE and TE profiles on the meridian plane and appropriately reducing the blade wrap angle,the RSI between the impeller and circumferential uneven flow fields upstream and downstream in the fixed frame tends to weaken,and the radial fluid force pulsation of impeller is also reduced accordingly.In order to study the mechanisms of internal unsteady flow and hydraulic excitation for the axial-flow RCP,in this thesis,an approach for monitoring and extracting the unsteady flow variables at points in the rotating frame of impeller was established.And the LEH pulsation was proposed to represent the characteristics of the complex unsteady flow around impeller.On the basis of the LEH pulsation at both sides of impeller and the pressure pulsation in the rotating frame of impeller,the RSI problem in the axial-flow RCP was studied,from the aspects of the disturbing action of rotor(impeller)on the static system and the reaction of stator(static hydraulic components)on the rotating flow region of impeller,respectively.And for both the static hydraulic component structures and the impeller hydraulic structure of the axial-flow RCP,effective improvement approaches for suppressing hydraulic excitation were proposed accordingly,based on the principle of improving circumferential uniformmity of the rotating and fixed flow fields.Related unsteady flow research methods,mechanisms of the RSI,and hydraulic excitation suppression approaches in this thesis,have reference value for the vibration control of the RCP,axial-flow pump and other pumps with similar structure forms. |
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