With the consistent pursuit of global countries for the goal of carbon neutrality, the urgency of energy saving and emission reduction is self-evident. Considering the critical proportion of pump consumption in the total energy consumption, improving its energy efficiency is significant to energy saving and emission reduction. Recently, many researches have aimed to improve parallel pump systems' energy efficiency. Due to the inflexibility of the existing parallel pump systems structure and the difficulty of equipment modification, the research methods mainly focus on improving the system control methods to enhance the system performance further. This paper introduces the latest research progress in modeling and control methods for parallel pump systems, firstly analyzing the energy consumption of existing parallel pump systems and proposing the possibility of energy saving in parallel pump systems. Then the system modeling and control methods are discussed in detail, comparing the traditional control methods with the emerging control optimization methods and discussing the parallel pump systems structure and monitoring. This review is expected to provide insights for future research on improving the performance of parallel pump systems.

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In order to further understand the distribution and motion of gas phase in the gas-liquid two-phase flow inside a centrifugal pump, the numerical simulation on gas-liquid two-phase flow in the centrifugal pump was carried out and the CFD method was verified by experiment test. The MUSIG model was used as the multiphase flow model, coupled with the Prince-Blanch model and the Luo-Svendson model to describe the bubble breaking and coalescence process. The influence of inlet gas volume fraction and liquid flow rate on the gas-liquid two-phase flow inside centrifugal pump was investigated. The results show that the proportion of large bubbles in impeller is higher than that in volute. Large bubbles are mainly at the suction chamber inlet and impeller inlet, and small bubbles are mainly at the impeller outlet and volute outlet. From suction chamber, impeller to the volute, the average diameter of bubbles decreases in turn. With the increase of inlet gas volume fraction, the proportion of small bubbles in the pump decreases. Also, the flow pattern inside the pump gradually changes from bubble flow to gas pocket flow and the average diameter of bubbles in each flow passage component increases. With the increase of liquid flow rate, the proportion of small bubbles in the pump increases. Meanwhile, the flow pattern gradually changes from gas pocket flow to bubble flow and the average diameter of bubbles in each flow passage component decreases.

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This paper presents a numerical simulation of a blocked pipeline and verifies the method’s applicability using existing experimental data. Wavelet analysis analyzes pressure signals of blockage types, lengths, rates, and locations inside the horizontal pipeline. A method is obtained for rapidly calculating the blockage location, length, and rate based on pressure wave reflection and transmission principles. The average error for blockage location detection using this method is 0.36%, while the error for blockage length detection is 1.47% and for blockage rate detection is 1.24%. The reasons that affect detection accuracy are given. Additionally, the pressure signals of two unique blockage models are analyzed. Combining the calculation results of multiple blockage locations and different blockage shapes shows that this method is suitable for detecting various blockage forms. The method’s applicability is also investigated when multiple blockages exist in the piping system. It is concluded that the method can only detect the blockage at the nearest position of the valve when there are multiple blockage locations in the piping.

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This paper presents an active method to control the pressure fluctuations induced by the rotating vortex rope (RVR) in a Francis hydro turbine model under part load conditions. The control method is based on the injection of axial or radial jets through a stagnant crown attached to the hydro turbine runner. A wide range of injection strategies are compared, and the effectiveness of suppressing pressure fluctuations is analyzed in terms of the spatial distribution of the jets and the flow rate required to suppress the oscillations. The experiments are per-formed on a fully automated aerodynamic test rig. The pressure fluctuations are quantified using data from the four acoustic sensors placed at a cross section in the cone of the hydro turbine draft tube. The best suppression of pressure fluctuations is achieved with a radial actuator. At a control flow rate of 2% of the main flow, the pressure fluctuations at the vortex rope frequency are reduced by 80% in terms of PSD compared to the baseline case without control. The presented control method will be useful for extending the operating range of Francis hydro turbines.

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Hydraulic efficiency is a crucial parameter in estimating the performance of hydraulic turbines. However, the flow rate makes such estimation challenging. Several methods have been developed over the years to measure the flow rate. The pressure-time method is an accurate and inexpensive alternative for flow rate estimation, based on transforming momentum into pressure during the deceleration of a liquid mass. The flow rate is obtained by integrating the differential pressure and the pressure loss history between two cross-sections. In the present work, three-dimensional (3D) computational fluid dynamics (CFD) analyses are performed to investigate in detail the influence of the head loss due to friction over the method accuracy when applied in developing flows. One important novelty of the CFD analyses is the use of the immersed solid method for the valve movement modeling for studying the pressure-time method, which is less expensive and more stable than the dynamic mesh method applied in previous CFD studies. The losses are investigated with the assumptions of constant, quasi-steady and unsteady friction factors and compared with detailed data obtained from CFD simulation. The calculated flow rate is not found to be precisely related to the initial pressure drop based on quasi-steady and unsteady friction factors in developing flows. Therefore, a friction factor correction coefficient is proposed and implemented, decreasing the error. The numerical results are validated with experimental data and compared with the dynamic mesh method.

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In the present study, we surveyed the performance of closed-type centrifugal pump with a single blade and its fluctuations through an experiment and a CFD analysis, and comparatively verified the blade outlet flow, with the objective of elucidating the internal flow structure and loss generation mechanism of the pump. Furthermore, we quantitatively evaluated each hydraulic loss on the pump and examined the relationship with the vortex structure in an impeller. The result showed that fluctuations in the impeller loss were notable at any flow rate with the maximum value at a blade phase angle of 133° when the best efficiency point flow rate. It suggests an impact of the vortex generated on the shroud side near the end of the blade outlet winding. While the impeller loss indicates similar behavior to the best efficiency point flow rate at a high flow rate, but its fluctuation was extremely large, and we found that such fluctuations are the behavior at a low flow rate was opposite to other flow rates.

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