Transient flow characteristics during variable operating conditions of the centrifugal charging pump in 1000 MW nuclear power plant

In order to study transient flow characteristics of the centrifugal charging pump during the process from the charging operating condition (Q = 34 m³/h) to the highest efficiency operating condition (Q = 110 m³/h), commercial software CFX was used to study the three-dimensional, unsteady, incompressible viscous flows. In this paper, the transient flow rate during the variable operating conditions was obtained from experimental data and immersed into CFX as the transient control function. The transient pressure and velocity in impellers, guide vanes, and double channels volute of the charging pump are analyzed through the simulation. The results show that the pressures in impellers increase gradually to the maximum and then decrease to the minimum in a rotational circle and looks like a sinusoidal curve. As the flow rate increasing, the fluctuant amplitude of the transient pressure tends to decrease. All transient velocities fluctuation becomes weaker and weaker and reduces to a minimum value in the 12th-stage impeller as time went on. The flow is untidy in the chamber and it causes large vortex at the small flow rate in the beginning of the variable operating conditions. The hydraulic performance of the pump is influenced both by the fluid acceleration and instantaneous evolutions of the vortex structure during the transient process. In addition, the fluctuation near the interface between impellers and guide vanes is bigger than others and the streamlines of flow get smooth under the rectification of each impeller and guide vane, which leads to the amplitude of pressure fluctuation unchanged basically in the last stage.