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• The synchronous measurement is used to study the chocked cavitation flow. • The evolution of chocked cavitation flow can be divided into three regions. • Cavitation average length has a two-stage linear relation with outlet pressure ratio. • Changes in cavitation areas correlate with pressure fluctuations. • The high reverse pressure gradient at the tail causes cavitation cloud oscillation. Experiments were conducted in this study to investigate the chocked cavitation characteristics and its oscillation mechanism in jet pump cavitation reactors (JPCR) under limited operation stage (LOS) utilizing a synchronous measurement system. The pulsation characteristics of cavitation in JPCR under various inlet and outlet pressures were analyzed by the processed high-speed camera images. Furthermore, correlation between cavitation and pressure pulsation as well as the mechanism of cavitation oscillation in JPCR under LOS are elucidated based on synchronized measurements. The results reveal that the typical jet choked cavitation flow field can be divided into three characteristic regions, i.e., stability region, oscillation region and collapse region. Changes in flow parameters cause variations in the areas of these three regions and shift the initial and collapse positions of cavitation. The time-averaged length of cavitation clouds varies linearly with the absolute pressure ratio at the outlet, corresponding to both stable and unstable LOS. Notably, the results reveal a clear correlation between the grayscale of cavitation clouds and pressure fluctuations over time, identifying the inverse pressure gradient as the primary cause of cavitation oscillation in the throat tube during unstable LOS. [ABSTRACT FROM AUTHOR]

Through the experimental verification, the accuracy of the cavitation jet feature captured by the coupling numerical calculation with different mesh types and different turbulence models is evaluated. Firstly, we built a high-speed jet experimental platform, and a high-speed camera and a paperless recorder are used to record the pressure, flow rate, and jet cloud oscillation of the jet pump in different states. The oscillation period and length of the jet cloud under different cavitation numbers are analyzed by the gray value method. The numerical results are compared with the experimental results. It is found that after the numerical calculation converges, the states of the jet cloud calculated by K–O and LES coupled with different meshes are periodically oscillating, while K-E does not. However, the maximum jet cloud lengths calculated by K-E and K–O turbulence models under different mesh types are nearly the same. Overall, the oscillation period calculated by the LES model is more in line with the experimental results, but its amplitude and maximum length are more different from the experimental results. In terms of capturing the jet cloud, critical pressure ratio, turbulent state and vapor volume fraction, the accuracy order of numerical calculation results are P–H (polyhedron-hexahedron mesh) ≈ P (polyhedron mesh) > H-T (hexahedral-tetrahedral mesh) > T (tetrahedral mesh), P–H ≈ P > T > H-T, P–H ≈ P > H-T > T and P–H > P > T > H-T, respectively. This research can provide more appropriate solutions for different concerns, as well as guidance for improving the accuracy and efficiency of simulations, and provides a basis for optimizing and developing specialized mesh types and turbulence models. • Based on K–O, the order of accuracy for capturing the jet cloud is P–H ≈ P > H-T > T. • Based on K-E, the order of accuracy for capturing h c r and P s is P–H ≈ P > T > H-T. • The I and ε obtained by the numerical calculation of P–H are the most accurate. • P–H captures the vapor volume fraction more accurately, H-T is the worst. [ABSTRACT FROM AUTHOR]

This paper studies the unsteady three-dimensional cavitating turbulent flow in a jet pump. Specifically, thefocus is on the unstable limited operation stage, and both the computational and experimental methods are used. In the experiments, the distribution of the wall pressure, as well as the evolution of cavitation over time, are obtained for a jet pump. Computation is carried out using the large eddy simulation, combined with a mass transfer cavitation model. The numerical results are compared with the experimental results, including the fundamental performances (the pressure ratio h and the efficiency η), as well as the wall pressure distribution. Both the experimental and computational results indicate that the evolution of the cavitation over time in a jet pump is a quasi-periodic process during the unstable limited operation stage. The annular vortex cavitation inception, development and collapse predicted by the large eddy simulation agree fairly well with the experimental observations. Furthermore, the relationship between the cavitation and the vortex structure is discussed based on the numerical results, and it is shown that the development of the vortex structures in the jet pump is closely related to the evolution of the cavitation. The cavitation-vortex interaction is thoroughly analyzed based on the vorticity transport equation. This analysis reveals that the cavitation in a jet pump dramatically influences the distribution and the production of the vorticity. The process of the annular cavitation inception, development, and collapse involves a significant increase of the vorticity. [ABSTRACT FROM AUTHOR]

Highlights • The proposed device has a much wider cavitating working range than present jet pumps. • The proposed device can simultaneously work as an adding device and a flow meter. • The adding liquid with different viscosity hardly affect the precision of flow rate measuring. Abstract To increase the operating range for cavitating quantitative mixing devices, a new jet pump is proposed. The distribution of pressure, velocity, turbulent dissipation rate, and vapor bubbles were studied numerically, and the influence of geometric parameters and flow ratio on the operating range were investigated experimentally. The proposed jet pump overlaps the high turbulence and low pressure regions at the nozzle exit, causing significant cavitation. When the cross section near the diffuser inlet is filled with vapor bubbles, the jet pump reaches its operating limit. Since the structure of suction chamber remains the same as conventional jet pumps, increasing secondary flow deforms the axisymmetric cavity cloud, which leads to quick reduction of the critical pressure ratio. Empirical curves are proposed to optimize the area ratio for given flow ratios, based on experimental tests of nine jet pumps. When the critical flow ratio <1.4% for a given optimal area ratio, the critical pressure ratio >0.8, which is significantly higher than current jet pumps. Reliability of the proposed jet pump was examined when operating as quantitative mixing device and flow meter simultaneously. When the flow ratio <4%, changes of area ratio, flow ratio, and viscosity of the working fluid have no effect flow rate measurement accuracy, and flow rate error <3.32% under all test conditions. [ABSTRACT FROM AUTHOR]

Abstract Experiments were conducted to investigate the cavity length pulsation characteristics in jet pumps with different area ratios during limited operation stage. Images of various cavitating flows were captured and analyzed to study the cavity length pulsation characteristics by high speed camera technology. It was found that the development tendency of time-averaged cavity length can be divided into two sections with different pulsation intensity by throat length. Further analysis indicated that the time-averaged cavity length is a function of area ratio and outlet pressure ratio independent of the inlet pressure. And the time-averaged cavity length decreases slowly and then faster with the increase of comprehensive parameters. Meanwhile, the cavity length pulsation can be decomposed into low frequency component and high frequency component. The pulsation intensity of low frequency component is relatively high during unstable limited operation stage, while it is at a low level during stable limited operation stage. Besides, smaller area ratio and inlet pressure result in larger pulsation intensity of low frequency component during unstable limited operation stage. The experimental points of high frequency component pulsation intensity collapsed around a V-shaped curve and it reached the minimum value when time-averaged cavity length is approximate to the throat length. Highlights • The development tendency of cavity length of jet pumps with different area ratio during limited operation stage is studied. • The relationship between time-averaged cavity length, flow parameter and area ratio is discussed. • The cavity length pulsation of jet pumps during limited operation stage is distinguished. • The dominant frequency distribution of cavity length pulsation is discussed. • The influence of area ratio and inlet pressure on the cavity length pulsation intensity is illustrated. [ABSTRACT FROM AUTHOR]

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Recent studies have shown that the collapse of cavitation bubbles in a jet pump can generate an extremely high pressure with many potential applications. The dynamics of the bubble is governed by the Rayleigh-Plesset equation. With the bubble dynamics equation and the heat and mass transfer model solved with the Runge-Kutta fourth order adaptive step size method, the oscillations of the bubble in the diffuser of the jet pump are assessed under varied conditions. To obtain the pressure variation along the diffuser, the Bernoulli equation and the pressure measured in experiment are coupled. The results of simulation show that a transient motion of the bubbles can be obtained in the diffuser quantitatively, to obtain the pressure and temperature shock in the bubble. Moreover, increasing the outlet pressure coefficient would result in a more intense bubble collapsing process, which can be used in the subsequent studies of the cavitation applications. The predictions are compared with experiments with good agreement. [ABSTRACT FROM AUTHOR]

The present paper describes a jet fish pump designed to safely convey fish in the aquatic industry due to its simple structure and reduced tendency to cause mechanical injury. High-speed imaging, physiology investigations and CFD simulations are used to demonstrate the impacts of the flow on the grass carp during transport in the jet fish pump for various operating conditions. The results show that none of the tested fish were dead, had organ injuries or had swimming problems after passing through the jet fish pump. The respiratory rates and most of the blood indexes of the tested fish were affected by the flow field in the pump, but they were able to recover to normal levels after just 24 h. The surface injuries such as descaling and operculum injuries were mainly caused by recirculation flows, shear flows and pressure gradients. Further analyses indicated that bruising was caused by the flow direction changes, with cavitation potentially causing eye injuries. A deflection number, C d , was proposed to describe the amount of flow direction changes for various operating conditions in the jet fish pump. The results show that, even though shear flows and pressure gradients are inevitable, the jet fish pump operating conditions can be optimized to reduce the risk of fish injuries. Recirculation regions and intensive cavitation should be avoided since they may cause serious injuries in the fish, reduce the fish transport rate and reduce the flow efficiency. These results provide a basis for improved jet fish pump designs. [ABSTRACT FROM AUTHOR]

In order to improve the jet pump cavitation, a new method of inhaling air into the low-pressure region was proposed, and its performance was investigated experimentally under different air suction quantity and cavitation levels. Test results show that the cavitation number increases with the air suction quantity increasing in a linear approximation fashion. Increasing air suction quantity corresponds to a sharp decrease in acoustic noise, especially for the severe cavitation. As the air suction quantity increases, the pressure fluctuation range and fluctuation variance both decrease in the downstream, which relieve the cavitation vibration damage and enhance the jet pump stability. In addition, the pressure loss ratio reduces by 0.95%–3.46% and the pressure ratio increases by 5.7%–18% due to the water–air cushion layer formed in the wall boundary. The marked effect on preventing cavitation damage and improving the pressure transmission performance of the jet pump proves that the new air suction method proposed is practical and effective. Therefore, it is believed that this study would lay an important foundation for the widespread application of jet pump in the future. [ABSTRACT FROM AUTHOR]

There is a dynamic equilibrium interface wave between the bubble region and the liquid region when a jet pump produces cavitation. The interface wave has an unstable boundary that moves backward and forward, and it is a pressure propagation front that causes the pressure change. The reason why the jet pump upstream pressures remain unchanged is because the interface wave has not arrived there. The interface wave moves upstream with the increase in outlet pressure. The region that it passes through experiences obvious pressure fluctuation and pressure rise. The nozzle cavity pressure rises slower than the throat cavity pressure, and the nozzle cavity has a lower pressure fluctuation frequency and smaller fluctuation range. Therefore, it is a good design for the jet pump to set the suction inlet near the nozzle cavity. In addition, the bubble region length, bubble region volume and bubble diameter decrease as the cavitation number increases in the jet pump. The bubbles completely vanish when the cavitation number reaches 1.53–1.59. Based on the above contributions, it is believed that this study will lay an important foundation for further research on the jet pump cavitation mechanism and cavitation prevention. [ABSTRACT FROM AUTHOR]

This paper describes an experimental study on water jet pumps with different diameters and nozzle-to-throat area ratios. The results revealed that the area ratio was an important parameter to characterize the maximum suction lift of the jet pumps, while their diameters had a negligible effect. All jet pumps reached the cavitation regime at a suction lift of about 8 mHO. In the non-cavitating region, it was found that the higher the area ratio, the higher the maximum suction lift for the same motive pressure head. However, the lower the area ratio, the higher the resistance to enter the cavitation regime. A dimensionless correlation was obtained for the non-cavitating region to describe the maximum suction lift as a function of a modified Thoma number and the area ratio. Curve fitting of experimental data also provided a dimensionless correlation to predict the onset of cavitation. Finally, applications of the results are presented. [ABSTRACT FROM AUTHOR]

Abstract: The critical cavitating flow in liquid jet pumps under operating limits is investigated in this paper. Measurements on the axial pressure distribution along the wall of jet pumps indicate that two-phase critical flow occurs in the throat pipe under operating limits. The entrained flow rate and the distribution of the wall pressure upstream lowest pressure section does not change when the outlet pressure is lower than a critical value. A liquid–vapor mixing shockwave is also observed under operating limits. The wave front moves back and forth in low frequency around the position of the lowest pressure. With the measured axial wall pressures, the Mach number of the two-phase cavitating flow is calculated. It’s found that the maximum Mach number is very close to 1 under operating limits. Further analysis infers a cross-section where Mach number approaches to 1 near the wave front. Thus, the liquid–vapor mixture velocity should reach the local sound velocity and resulting in the occurrence of operating limits. [Copyright &y& Elsevier]