Transient rear cavity vortex flow in a spherical-casing nuclear reactor coolant pump

The next-generation nuclear reactor coolant pumps (NRCP) have gradually transitioned to mixed-flow designs due to their advantages of a wide operating range, broad flow range, and high efficiency. These pumps often adopt unconventional spherical casings, resulting in complex internal flow dynamics. Therefore, a comprehensive analysis of NRCPs' internal flow field structure is critical for evaluating their operational stability. This investigation uses large eddy simulation to analyze the transient flow inside the spherical casing mixed-flow NRCP. A new type of large-scale strip-like vortex inside the rear cavity of the spherical casing has been found, named the rear cavity vortex, and its pressure pulsation characteristic is analyzed. The rear cavity vortex has three stages. This investigation identifies 7.09 Hz as the characteristic frequency of the rear cavity vortex, recognized as its self-rotation frequency. Additionally, 24.82 Hz is identified as the characteristic frequency of front vortex shedding. The results of this investigation indicate that optimizing the geometric design of the spherical casing might help weaken the intensity of the rear cavity vortex, thereby mitigating its impact on the operational stability of the NRCP. This provides valuable guidance for improving the efficiency and operational reliability of the NRCP.