Investigation of the flow characteristics in a main nuclear power plant pump with eccentric impeller

The main pump is a key component in nuclear power plants. The operating stability and security of the main pump is crucial to the power plant operation. In this study, CFD simulations based on the detached eddy simulation method were used to study the flow characteristics in the pump. The overall performance, the pressure pulsations and the forces on the impeller are studied in detail. The predicted pump head and efficiency agree well with experimental data around the design flow condition even though undesirable flow is found in the guide vanes and circular volute. However, the CFD simulations did not correctly predict the pressure pulsation frequency even for the design flow condition. The experiments showed pressure pulsations at 50 Hz and at multiples of 50 Hz that were not predicted in the CFD simulation. After a small eccentricity was added to the impeller in the simulation, the 50 Hz pulsation was then captured with each impeller revolution in the CFD simulations at multiple pressure pulsation monitoring points. The amplitudes of the 50 Hz frequency and its multiples increase with the impeller eccentricity. Thus, the impeller eccentricity influences the pressure pulsations and the axial and radial forces. The impeller eccentricity has an important effect on the operating stability and security of the main pump. In addition, simulations must consider the impeller eccentricity for accurate analyses of the main pump in nuclear power plants.