To investigate the collector discharge pressure fluctuation characteristics and the related factors in a 1 000 MW nuclear reactor coolant pump, steady and unsteady 3dimensional numerical simulation was conducted to depict the inner flow inherence and detailed pressure content of a domestic pump model. Both time and frequency domain analysis were further put forward. It is shown that reverse flow is one of the reasons that cause the pressure fluctuations at the joint of the collector and the discharge. Obvious pressure fluctuations exit at the collector discharge and the adjacent area. In addition, the more the operation condition deviates from the design point, the more severe the pressure fluctuations are. The fluctuation amplitude in the upper passage is higher than that in the lower passage. The mean amplitude are 11.5%, 9.62% and 13.78% respectively in the upper passage, while they are 13.62%, 12.53% and 15.79% respectively in the lower one under the flow rates of 0.9Q, 1.0Q, and 1.2Q. At the adjacent diffuser vanes, the fluctuation amplitude near both sides of the casing wall is larger than that near the midspan line. In the regions far from the diffuser outlet, the fluctuation amplitude is increased gradually from the top side wall of casing to the bottom one. The shaft rotating frequency is the major factor influencing pressure fluctuation at ever monitor point when the pump is working at the design point. However, both the shaft rotating frequency and the blade passing frequency are the main factors when it works at offdesign points.
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