As crucial equipment in the industrial field, the stable operation of centrifugal pumps has drawn noteworthy attention. Relevant studies in the open literature have shown that intense pressure fluctuations have a major effect on the reliability and lifetime of centrifugal pumps. In the present paper, the pressure fluctuations in the centrifugal pumps are discussed in detail from different perspectives. The details of the studies are as follows. Firstly, the pressure fluctuation characteristics in centrifugal pumps are studied without considering clearance flow. Secondly, the pressure fluctuation property is investigated in detail for the pumps, with consideration for clearance flow. The pressure fluctuation characteristics in the wear ring, the pump-chamber clearance region, and the main stream region are studied, and the effect of clearance flow on the external performance of the pumps is analyzed. Thirdly, measures to reduce the pressure fluctuations and forces are summarized to improve the operational reliability of centrifugal pumps. Finally, conclusions and future research perspectives in the field of centrifugal pumps are presented. This review presents the research highlights and progress in the field of pressure fluctuations, which is beneficial to the stable operation of centrifugal pumps in engineering.

The flow and heat transfer characteristics in micro-tube are very important research fields. In order to study the influence of the Reynolds number on the overall characteristics of flow and heat transfer, a 510 mm long micro-tube with dimples was constructed. Thirty-five different working conditions are considered, and the Reynolds number is between 1500 and 8100. At the same time, the change of physical properties of coolant with temperature is considered. The reliability of numerical simulation results is verified by the grid independence verification and the comparison of experimental data. The results show that the dimple will promote the instability of the flow state and improve the heat transfer efficiency. The flow state evolution formed in the stream-wise direction is basically similar, and its fully developed position remains at 76 mm, which is independent of the Reynolds number. For the fully developed region, the partial derivation of static pressure in the stream-wise component has a quasi-linear relationship with the stream-wise direction. With the development in the stream-wise direction, the partial derivation of static temperature in the steam-wise component decreases. With the increase of Reynolds number, the friction factor f and heat transfer factor j decrease. The ratio of factor heat transfer f to Reynolds number relative collapses for the different cases, especially when the Reynolds number is larger than 3800. The heat transfer factor j is an exponential function of the Reynolds number and decreases with the increased Reynolds number.

This study uses large eddy simulation to investigate the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate and constant rotational speed. Five different oscillation frequencies ( f/f0 = 1.0, 1.2, 1.5, 2.0, and 3.0, where f0 indicates one-ninth of the rotational speed) are selected to isolate the influence of oscillation frequency on the flow characteristics. Studies show that the pressure deviation between dropping and rising stages concentrates at the impeller inlet at instantaneous 0.5  Qd ( Qd is the design load), and its value increases with the increase in oscillation frequency. The lowest period of many flow characteristics, including pressure fluctuation and head, equals to that of flow rate. The differences in pressure fluctuation between adjacent channels decreases with the increase in oscillation frequency. The first and second dominant frequencies of pressure fluctuation are mainly affected by the oscillation frequency in the nonstall passage, and they have an important relationship with the stall vortex in the stall passage. With the increase in oscillation frequency, the amplitude of lowest order head pulsation increases, and the high order head pulsation gradually weakens. The average head is approximately 2.36 m.