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In order to study the unsteady flow and vortex characteristics of tongue cavitation, numerical calculation is carried out for the whole flow channel given different conditions. Then, the calculation results are verified experimentally. The results show that after the occurrence of tongue cavitation in the centrifugal pump, it deteriorates with the decrease of NPSHa. However, when NPSHa is reduced to 3.78 m, it does not change significantly anymore with the decrease of NPSHa. The extrusion of fluid by the vapor at the tongue promotes the formation of the separation vortex, and the re-jet flow caused by the separation vortex leads to vapor shedding. The frequency of cavitation shedding is consistent with the frequency of vortex shedding. In the vorticity transport equation, the relative vortex stretching term and the relative vortex dilatation term dominate the vapor shedding by controlling the change in vorticity. The baroclinic torque term mainly affects the change of vorticity at the vapor-liquid interface, but to a much lesser extent than the first two terms. [ABSTRACT FROM AUTHOR]

In this study, the critical submergence of deep well pumps is analyzed. The critical submergence, which is an important parameter for centrifugal pumps and water intakes that usually have a certain diameter, is determined using dimensionless quantities. The innovative aspect of this study is that three different water inlet opening models are created for two shaft pumps with different nominal diameters, these models are related to the water inlet diameters and the critical submergence is defined using dimensionless quantities. The critical submergence of the pumps was determined using a vacuum measurement method and the critical submergence of each model at different flow rates was compared with Froude number dependent submergence equations developed by other researchers. The aim of this study is to determine the critical submergence of the pumps and to use the flow models developed at these depths with the aid of mathematical equations to ensure the operation of the pumps in the reliable zone (vortex-free). The physical models were found to be effective for vortex formation depth and vortex shape. The physical models found Fcr (critical Froude number) ≤1.40 for pump P1 and Fcr ≤1.44 for pump P2, these values can also be used to determine the suction lift of the pumps. The critical Weber and Reynolds numbers decrease as the water suction area of the pumps increases. Considering the depth of vortex formation, it would be appropriate to use the original (D0) physical models for both pumps. As a result, dimensionless quantities can be used to determine the critical submergence of deep well pumps. [ABSTRACT FROM AUTHOR]

The objectives of this paper are to pursue an accurate numerical method of unsteady cavitating flow at a reasonable calculation cost and investigate the unsteady cavitating flow characteristics of a centrifugal pump. Firstly, the cavitating flow simulations of a centrifugal pump were performed using the partially-averaged Navier–Stokes (PANS) turbulence model and its improved model to evaluate the numerical methods based on experimental data. Compared with the experimental results, the improved PANS turbulence model can better predict the cavitating flows in the pump and has better applicability. Further, the unsteady cavitating flow characteristics of the centrifugal pump, such as the vapour volume fraction, the cavitation-vortex dynamics and the pressure and head fluctuations, were simulated by improved PANS model and discussed. The liquid flow vortex at the end of the cavitation in the impeller is an important reason for the periodic change of the cavitation shape. The periodic change of cavity volume has a certain impact on the pressure pulsation in the impeller and the pump head. [ABSTRACT FROM AUTHOR]

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To study the cavitation and induced pressure pulsation characteristics of the volute tongue of the centrifugal pump, the full channel numerical calculation of the centrifugal pump under different flow rates and available net positive suction head conditions was conducted, and the numerical calculation results were verified by experiments. The results show that cavitation near the tongue of the centrifugal pump occurs under large flow conditions, which is mainly caused by the separation vortex formed by flow separation. The frequency of vapor bubbles shedding at the tongue is equal to that of the separation vortex, both of which are blade passing frequencies. The change of vapor bubble volume in the process of vapor bubble shedding is consistent with the change trend of vorticity in the process of vortex shedding, both of which first increase and subsequently decrease. The pressure pulsation periods of different monitoring points near the tongue are identical. The amplitude of pressure pulsation near the impeller near the tongue is larger. The amplitude of pressure pulsation around the tongue decreases when tongue cavitation occurs. The pressure pulsation at this place mainly depends on the influence of the separation and attachment vortex at the tongue and the dynamic and static interference between the impeller and the tongue. The main frequency amplitude of pressure pulsation near the tongue gradually decreases with the occurrence and development of tongue cavitation, and broadband pulsation appears in the low-frequency band. [ABSTRACT FROM AUTHOR]

• Proposed an optimization strategy based on the particle swarm algorithm (PSO) and least squares support vector regression (LSSVR) machine to enhance the efficiency of the Multistage LNG cryogenic submersible pump. • Achieved a 0.57% increase in head and a 2.72% improvement in efficiency of the LNG cryogenic submersible pump through the optimization of the impeller structure using the PSO-LSSVR method. • Verified the accuracy of the PSO-LSSVR method by comparing the results with computational fluid dynamics (CFD) calculations, demonstrating a relative error within 3%. • Utilized the enstrophy dissipation theory to quantitatively analyze and reduce energy loss in the impeller, achieving a maximum reduction of 18%. • Investigated the distribution and mechanism of vortex generation inside the impeller using the Q-criterion and the relative vortex transport equation. • Suppressed the horseshoe vortex structure at the leading edge of the optimized impeller blade and reduced the dominant terms responsible for vortex structure evolution. • Provides valuable insights and references for the optimal design of Multistage LNG cryogenic submersible pumps. The Multistage LNG cryogenic submersible pump is one of the crucial power equipment in LNG transport process. However, the high hydraulic losses and low efficiency of this pump make it necessary to optimize the structure of its impeller in order to reduce energy losses. In this study, an optimization strategy based on particle swarm optimization (PSO) and least squares support vector regression (LSSVR) machine is proposed to optimize the structure of impeller. The optimization of the impeller structure with the PSO-LSSVR method increased the head and efficiency of the LNG cryogenic submersible pump by 0.57% and 2.72%, respectively. Comparing the calculation results of PSO-LSSVR method with the CFD results, we found that the relative error between them don't exceed 3%, which verified the calculation accuracy of the method. Then, an enstrophy dissipation theory is introduced to quantitatively analyze the pump energy loss. Comparing the impellers before and after optimization revealed that the maximum reduction in impeller energy loss was 18%.. The distribution and mechanism of vortex generation inside the impeller were analyzed with the Q-criterion and the relative vortex transport equation. The relative vortex transport equation revealed that the horseshoe vortex structure at the leading edge of the optimized impeller blade was suppressed, and the relative vortex stretching term and the Coriolis force term, which dominate the evolution of the vortex structure, were reduced. This study will provide related reference for the optimal design of Multistage LNG cryogenic submersible pumps. [ABSTRACT FROM AUTHOR]

Unsteady pressure pulsation and fluid force induced by flow instabilities in the centrifugal pump is an important cause of vibration, which is detrimental to the safe operation of the pump. In this study, we numerically investigated the pressure pulsation and radial force in a low-specific-speed centrifugal pump by using the detached-eddy simulation method. We also performed a vibration displacement experiment on the shaft of the centrifugal pump. The vortex identification method was introduced to clarify the internal correlation between unsteady flow structures with pressure pulsations. The results showed that the pressure pulsations at the impeller outlet were closely associated with the periodic vortex shedding from the blade pressure surface. The rotor-stator interaction between a relatively big trailing vortex core and volute tongue generated larger pressure pulsation and radial force in the pump at a low flow rate. Under a large flow rate, the trailing vortex core was easily broken and dispersed, and this resulted in smaller pressure pulsation and radial force compared with that at a low flow rate. Under the design flow rate, the pressure pulsation intensity and the radial force in the impeller were smaller than that under the off-design flow rate. Compared with the spectra between the radial force on the impeller and radial displacement on the shaft, they both presented higher amplitude at the shaft frequency. The vibration of the pump shaft was closely related to the radial force on the impeller. [ABSTRACT FROM AUTHOR]

Inducers in centrifugal pumps are generally placed upstream to increase the pressure before the impeller and prevent cavitation occurrence. Their general goal is to obtain a positive impact on the performances of a pump in a two-phase regime. Cavitation phenomenon has been the subject of many studies; however, the influence of the presence of dissolved gas in the liquid pumped under particular operating conditions remains not sufficiently explored. To the best of our knowledge, aviation jet fuel cavitation is moderately documented. In the present work, we conducted an experimental study on two three-bladed axial inducers at partial flow rates only in cavitating and noncavitating regimes. The experimental work used aviation jet fuel, water, and water with dissolved content of CO2 at constant temperature in two closed loops with transparent test sections. In one tank, a specific device is placed to inject a controlled quantity of CO2 and to dissolve it in water. We achieved a comparison of the flow dynamics through the use of a high-speed camera with a sampling rate of 1000 Hz. The results show inducers' water-CO2 cavitation performances to be in good agreement with aviation jet fuel cavitation results. [ABSTRACT FROM AUTHOR]

• The irreversible energy losses within the centrifugal pump for cavitation flow has been studied. • The impeller has the most to generate irreversible energy losses among all the components of centrifugal pump. • Most of the losses within the impeller take place at the impeller outlet and upstream of blade suction surface. • The velocity pulsation caused by high-speed vortex is considered as the main reason for total entropy production. The objective of this paper is to investigate the characteristics of irreversible energy loss caused by cavitation flow in centrifugal pump. The entropy production theory with computational fluid dynamics (CFD) is employed to analyze the relationship between flow field details of cavitation flow and irreversible flow loss. The accuracy of the simulations is ascertained by comparing the cavitation performance curve and cavity distribution of the pump obtained numerically and experimentally. The predicted results show that the entropy production is consistent with the energy loss, and the energy loss in the impeller is large. Further, the distribution of entropy production and flow details in the impeller are analyzed. It is found that the serious cavitation flow changes the flow field structure and the distribution area of maximum entropy production, the turbulence velocity fluctuation is the main reason for the increase of the total entropy production, and the high-speed vortex has great influence on the irreversible flow loss. [ABSTRACT FROM AUTHOR]

The pressure fluctuations of high-speed centrifugal pumps are the hotspot in pump research. Pressure fluctuations is differ for different structural designs and flow structures. High-speed centrifugal pumps are usually designed to increase efficiency with an enlarged flow design at a low specific speed, which changes the structure of the pump. In order to analyze the pressure fluctuations of a high-speed centrifugal pump with an enlarged flow design, the pressure was measured, and the flow field of the pump was simulated with different flow rates. Through analysis, we found that pressure fluctuations varied periodically and was consistent with the blade frequency. The pressure fluctuations at the guide vane and the interference region were also closely related to the vortices at the impeller outlet, which changed differently at different flow rates. The results showed that the high-speed centrifugal pump with an enlarged design had better performance at a large flow rate. The results in this paper can provide reference for the design of a pump that should be designed with the enlarged flow method. [ABSTRACT FROM AUTHOR]

Pump as turbines (PATs) are widely applied for recovering the dissipated energy of high-pressure fluids in several hydraulic energy resources. When a centrifugal pump operates as turbine, the large axial vortex occurs usually within the impeller flow passages. In view of the structure and evolution of the vortex, and its effect on pressure fluctuation and energy conversion of the machine, a PAT with specific-speed 9.1 was analyzed based on detached eddy simulation (DES), and the results showed that vortices generated at the impeller inlet region, and the size and position of detected vortices, were fixed as the impeller rotated. However, the swirling strength of vortex cores changed periodically with double rotational frequency. The influence of vortices on pressure fluctuation of PAT was relatively obvious, deteriorating the operating stability of the machine evidently. In addition, the power loss near impeller inlet region was obviously heavy as the impact of large axial vortices, which was much more serious in low flow rate conditions. The results are helpful to realize the flow field of PAT and are instructive for blade optimization design. [ABSTRACT FROM AUTHOR]