The operational stability of the nuclear reactor coolant pump (RCP) will directly affect the safety of the nuclear power plants (NPPs). A comprehensive analysis of the dynamic characteristics of the ...internal flow structure in the RCP is extremely important to assess its operational stability. Because the unsteady pressure characteristics of the spherical casing wall of the RCP and the dynamic flow field inside the RCP are complicated, it is highly demanding to be accurately measured by a reliable approach. Dynamic pressure pulsation and Laser Doppler Velocimetry (LDV) measurements have been carried out on the spherical casing wall and internal flow of the RCP under different operating conditions. Based on the pressure pulsation measurement, it is convinced that different unsteadiness flow structures directly affect the pressure pulsation characteristics, which will generate various excitation signals. The intercoupling between rotor-stator interaction (RSI) and the collision of the fluid discharged from the diffuser with the circulating flow to the casing bottom is the main reason for leading to strong pressure pulsations. Dynamic LDV measurement result shows that there is a significant counterclockwise periodic vortex shedding from the diffuser blade trailing edge, especially under high flow rate (1.2QN), which is also the main reason of strong velocity pulsations. The core of this paper is to comprehensively elaborate the dynamic flow characteristics in such a complex hydraulic machinery through combining multiple dynamic measurement methods. Moreover, an exhaustive understanding of dynamic flow characteristics is the basis for optimizing the RCP. The experimental results can provide ideas and basis for the optimization of the RCP with stable operation characteristics.
•Combination of LDV and pressure pulsation measurement was used.•Unsteady pressure and velocity pulsations characteristics were comprehensively analyzed.•The internal causes of the strong pulsation regions were discussed.•Comprehensively elaborated the dynamic flow characteristics in a nuclear reactor coolant pump.•Mechanism of dynamic flow field in the RCP was preliminarily revealed.
The nuclear reactor coolant pump transferring heat energy inherently brings with it the unsteady flow and inevitably threatens to the safe operation of the pump unit, especially with the pressure ...pulsation induced by the rotor-stator interaction. In this paper, the characteristics of pressure pulsation of the diffuser in a nuclear reactor coolant pump were investigated by the numerical simulation with experimental validation. Pressure pulsation signals measured synchronously from sensors mounted on the radial diffuser of a model pump were analyzed via Welch’s method. Frequency components induced by the rotor-stator interaction can be revealed by the diameter mode analysis method. The pressure pulsation of the diffuser is dominated by the blade passing frequency and its harmonics, which are free from the effect of flow rate and rotational speed while the corresponding amplitudes are easily affected by different operational conditions and measuring positions. The non-uniformity is much more affected by the rotational speed than the flow rate. This research is helpful for further work to reduce the pressure pulsation for the reactor coolant pump.
•The detailed error analysis between experiment and LES method is made.•The experimental and LES method are combined to analyze unsteady pressure pulsations.•The mechanism of instantaneous vortical ...flow structure is preliminarily revealed.•The vortical flow characteristic is the main reason that causes complex excitation frequencies.
The instantaneous vortical flow structure is one of the typical flow structures inside the nuclear reactor coolant pump (RCP), which would cause the unsteady pressure pulsations, vibrations of the unit and fatigue of components. Due to high safety requirement of the RCP during the actual operation of the nuclear power plants (NPPs), revealing instantaneous nature of vortical flow structure and its pressure pulsation becomes a crucial issue for studying the internal flow mechanism of the RCP. The purpose of this study is to shed comprehensive light on the pressure pulsation and instantaneous vortical flow structure in the RCP by using the experimental method and the numerical simulation method. Based on the result of comparison with the experiment and numerical simulation, it can be considered that the LES method can better identify instantaneous nature of vortical flow structures in the low frequency band. The instantaneous vortical flow structure is attached to the impeller RBPS (rotor blade pressure surface) and transient jet wake vortex flow structures between the impeller and diffuser under the rotor-stator interaction effect are fairly obvious by Q-criterion. On the other hand, in the axial-vorticity component distribution, the rotor-stator interaction effect between the impeller and diffuser cannot be clearly revealed. From the three-dimensional structures, the main vortex structures are in the front and back cavity of the right-hand side near the discharge nozzle and the right-hand side below the discharge nozzle in the spherical casing. Meanwhile, combined with pressure spectrum, it is convinced that their unsteady characteristic is the main reason that causes complex excitation frequencies in the low frequency band of the right-hand side near the discharge nozzle.
•The influence of the different diffuser BTE profiles on the flow instability in RCP is explored.•The pressure pulsations are extremely asymmetrical in the circumferential direction.•Two high ...axial-vorticity magnitude regions are captured on the mid-span.•The appropriate diffuser BTE profile would also diminish Von Kármán vortices.
The shedding flow structures from the diffuser blade trailing edge, usually known as Von Kármán vortices, are complicated and crucial to the safe operation of the nuclear reactor coolant pump (RCP), if the shedding frequency reaches the resonant frequency of the diffuser. In the present study, numerical investigation is conducted to analyze the effect of the diffuser blade trailing edge (BTE) profile on the flow instability in a nuclear reactor coolant pump. Five typical diffuser BTEs are analyzed including original trailing edge (OTE), circular trailing edge (CTE), suction surface trailing edge radius 45mm (STER 45), suction surface trailing edge radius 60mm (STER 60) and suction surface trailing edge radius 75mm (STER 75). Results show that by changing the diffuser BTE profile, the vortex shedding intensity from the trailing edge would be diminished, and unsteady flow structures in the spherical casing are more uniform with the well modified diffuser BTE profile. When adopting the cases of STER 45, STER 60 and STER 75, pressure pulsations decrease at the diffuser outlet, but increase at the right side of spherical casing wall. From axial-vorticity distribution, it is indicated that the appropriate BTE profile can effectively prevent flow separation and change evolution of separate flow especially near the discharge nozzle. Besides, it would also diminish Von Kármán vortices from the diffuser BTE, and improve the RCP hydraulic efficiency.
In this paper, we investigate the feasibility of a strategy of fault detection capable of controlling misclassification probabilities, i.e., balancing false and missed alarms. The novelty of the ...proposed strategy consists of i) a signal grouping technique and signal reconstruction modeling technique (one model for each subgroup), and ii) a statistical method for defining the fault alarm level. We consider a real case study concerning 46 signals of the Reactor Coolant Pump (RCP) of a typical Pressurized Water Reactor (PWR). In the application, the reconstructions are provided by a set of Auto-Associative Kernel Regression (AAKR) models, whose input signals have been selected by a hybrid approach based on Correlation Analysis (CA) and Genetic Algorithm (GA) for the identification of the groups. Sequential Probability Ratio Test (SPRT) is used to define the alarm level for a given expected classification performance. A practical guideline is provided for optimally setting the SPRT parameters' values.
As the unique rotating component, the impeller is the core component of a nuclear reactor coolant pump (RCP), the dynamic properties of the impeller are critical for the safe operation of the whole ...reactor. The purpose of this study was to shed comprehensive light on the pressure pulsation and modal properties of a scaled RCP impeller via experimental and numerical methods. The numerical model was validated by an experiment connecting the pressure pulsation signals at the diffuser inlet, and a good agreement was obtained between the numerical and experimental results. Pressure pulsation acting on the impeller's blade is mainly dominated by the impeller rotating frequency, the vane passing frequency, and the double blade‐passing frequency, and the pressure pulsation acting on the blade's pressure surface is more intense than on the suction surface. The modal properties were obtained via the modal test and numerical methods with the impeller suspended as a free body in the air and submerged inside water. The reduction in the impeller natural frequencies was between 31.63% and 37.77% for the corresponding mode shape due to the added mass effect of the fluid. Based on the pressure pulsation characteristics acting on the impeller and the natural frequency of the impeller, it is considered there is no risk of resonance in the impeller. Finally, it is expected that the present work can provide scientific guidance to avoid hydraulic resonance in nuclear reactor coolant pumps.
The unsteady pressure pulsation characteristics and the modal behavior of a scaled reactor coolant pump impeller are investigated via experimental and numerical methods. The added mass effect of the surrounding water is analyzed, and the risk of impeller resonance is studied as well.
In order to study the influence of eccentricity on hydrodynamic characteristics of nuclear reactor coolant pump under different cavitation conditions, five different schemes were obtained by ...analyzing and optimizing the existing structural schemes. Based on the RNG k-ε model (Renormalization Group with k-epsilon turbulence models) and two-fluid two-phase flow model, the unsteady numerical analysis and test verification of different designed schemes are carried out by using the flow field software ANSYS CFX. The results of research show that different eccentricities will affect the nuclear reactor coolant pump’s head under different cavitation conditions, and the corresponding head in the scheme with the eccentricity of 5mm under the fracture cavitation condition is lower than that of the other schemes. When the impeller rotates at a certain angle from the initial position under critical and severe cavitation conditions, the radial force acting on the rotor system will fluctuate greatly. Under the condition of fracture cavitation, the radial force changed periodically and the resultant force value is small. Compared to the original scheme, the peak value of radial force is 6° clockwise after eccentricity of the impeller appeared. With the aggravation of cavitation condition, the axial force value of impeller decreases, but the corresponding amplitude of the impeller increases. Under critical and severe cavitation conditions, the maximum axial force amplitude of the nuclear reactor coolant pump appears in the two times blade frequency, and in the broken cavitation condition, the maximum axial force amplitude appears at the shaft frequency. When the eccentricity is 20 mm, the axial force fluctuates most under critical and severe cavitation conditions, and when the eccentricity is 10 mm, the corresponding axial force is smaller than that of the original scheme. When the eccentricity is 5 mm, the axial force on the impeller is the smallest, but the amplitude is the largest under the condition of fracture cavitation.
A hydraulic experimental platform for the assembly of stator components was developed,and the simulation on this system was performed based on software AMEsim.Characteristics of the system,such as ...the pressure and the displacement,were analyzed.The results guide design of the hydraulic system of experiment platform for the assembly of the stator.
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