Pressure pulsation analysis of a large reactor coolant pump experimental loop based on field test and numerical simulation

The vortex structures may cause unstable pressure pulsations and vibrations in Reactor Coolant Pumps (RCPs). During the CAP1400 RCP tests, flow-induced vibrations were observed at both the inherent frequency (3.66 Hz) and the blade passing frequency (f_BPF). The amplitude of the vibrations at the inherent frequency exceeded the allowable limit, resulting in necessary shutdown inspections. This study, based on field test data, thoroughly analyzed the characteristics of low-frequency (below 10 Hz) pressure pulsations in the complex experimental loop and identified the main occurrence area as the outlet of the RCP and the inlet of the valve. We also briefly analyzed the amplitude variations of the f_BPF and 2f_BPF in the experimental loop, observing similar periodic variations at specific frequencies under different rotational speeds. Additionally, as the rotational speed increased, the amplitudes of both the low-frequency and f_BPF pressure pulsations significantly increased. Numerical simulations revealed the flow field within the experimental loop. The interaction between the flow from the RCP diffuser outlet and the volute, as well as the sudden change in the flow channel area within the valve, are the main mechanisms forming vortices. These findings provide important test and theoretical foundations for further studies on flow-induced vibration problems in mixed-flow RCPs and experimental loops.