Analysis of the internal characteristic changes of the nuclear main pump under forward rotation conditions

To investigate the internal flow characteristics and energy dissipation of the nuclear main pump, a full-flow numerical simulation was conducted on a third-generation nuclear main pump model. The internal characteristics of the nuclear main pump under forward rotation conditions were analyzed based on Fast Fourier Transform (FFT) and entropy production theory. The results show that under pump conditions, the time-domain diagrams of pressure pulsation in each flow passage component exhibit obvious periodic fluctuations, with the main frequency appearing at the blade frequency, indicating typical rotor-stator interaction characteristics. However, under braking conditions, only the guide vanes maintain periodic pulsation, while the flow in the impeller and volute presents a turbulent state, with the main frequency of the volute migrating to the low-frequency region. Entropy production analysis reveals that the impeller always has the highest energy dissipation under forward rotation conditions. Specifically, under pump conditions, the high entropy production areas of the impeller are mainly distributed in the outlet region and on both sides of the blades, while the wall entropy production is concentrated at the leading edge of the blades and the trailing edge of the front shroud. Under braking conditions, the high entropy production areas shift to the suction side of the blades and the inlet region, and the wall entropy production is mainly distributed on the pressure side of the blades and at the inlet. The change in this distribution characteristic reflects significant differences in flow separation and energy loss mechanisms under different operating conditions.