Vortex pumps play a crucial role in industrial and municipal settings by transferring high-viscosity and particle-laden fluids. However, their performance and reliability are significantly compromised by cavitation. Identifying and diagnosing cavitation promptly is essential for maintaining the proper operation of vortex pumps. The use of current signals as a non-invasive monitoring method has shown great promise in detecting multi-cavitation states. The proposed method integrates dual-tree complex wavelet transform with variational mode decomposition to decompose current signals into multiple modes. Subsequently, the Bayesian optimized locally weighted K-nearest neighbor algorithm is employed to accurately identify multi-cavitation states. High-speed photography is also utilized to observe the incipient, developing, and collapsing phases of cavitation. The results indicate that the proposed method achieves a detection accuracy of 96.67% at a flow rate of 40 m³/h, outperforming other flow conditions. The recognition accuracy reaches 98.33% under stable flow conditions, while accuracies of 92.33% and 93.67% are observed for flow rates of 35 m³/h and 45 m³/h, respectively. The overall average recognition rate across all tested flow conditions is 94.22%. This methodology not only demonstrates high effectiveness in identifying cavitation states but also offers a reliable and practical solution for fault diagnosis in fluid mechanical systems. It significantly contributes to the improvement of operational efficiency, reliability, and maintenance strategies in industrial and municipal pumping systems.

To promote the development and application of the liquid–gas jet pump (LGJP), the research status of its design theory, internal flow mechanism, structural optimization and practical application are reviewed. The development history of the LGJP is briefly reviewed, the latest research and application progress of the LGJP is introduced, and the pulse-type of LGJP, especially the centrifugal jet vacuum pump (CJVP), is emphatically discussed. The research and development direction of the LGJP is analyzed and proposed: CFD will be more deeply applied to the mechanism research and performance improvement of the LGJP; the diversity and heterogeneity of the fluid medium and its influence on the internal flow mechanism are the research highlights of the LGJP; it is urgent to study the gas–liquid two-phase flow and pumping mechanism inside the pulsed liquid–gas jet pump (PLGJP), especially the CJVP.

Jet fish pumps are efficient hydraulic machinery for fish transportation. Yet, the complex flow phenomenon in it is the major potential risk for damage to fish. The dangerous flow phenomena for fish, such as radial pressure gradient and exposure strain rate, are usually controlled by the structural parameters of jet fish pumps. Therefore, the injury rate of fish can be theoretically decreased by the structural optimization design of jet fish pumps. However, there is a complex nonlinear relation between flow phenomena and key structural parameters. To solve this problem, the present paper established a complex mapping between flow phenomena and structural parameters, based on computational fluid dynamics and a back-propagation neural network. According to this mapping, an NSGA-II multi-objective genetic algorithm was used to optimize the structure of jet fish pumps. The results showed that the optimized jet fish pumps could reduce the internal radial pressure gradient, exposure strain rate and danger zone to 40%, 12.5% and 50% of the pre-optimization level, respectively. Therefore, the optimized jet fish pump could significantly reduce the risk of fish injuries and keep the pump efficiency at a high level. The results could provide a certain reference for relevant structural optimization problems.

More and more activities have caused significant damage to the river environment, among which a typical problem of blocked fish migration is constantly attracting people’s attention. Nowadays, fishways are essential hydraulic facilities to solve such problems. Although a different fishway has a particular blocking effect on the water flow, the flow velocity of the vital positions of fish migration in the fishway could still be relatively high locally, which may pose a certain challenge to the fish migration (the higher flow velocity could lead to the increase in migratory energy consumption of fish). Therefore, further exploration of fish passing facilities may be required. As a check valve without movable parts, the Tesla valve is expected to be used in fish passing facilities because of its substantial obstruction to the reverse flow of internal fluid. This paper conducted numerical simulation experiments on the fish passage pipeline designed based on Tesla valves using the RNG (renormalization group) k-ε model. Grass carp were selected as the primary analysis object, and the simulation results were analyzed from the perspective of turbulence characteristics. The results showed that the fish passage pipeline based on the T45-R Tesla valve was better than that on the GMF (Gamboa, Morris and Forster) Tesla valve in velocity control. The velocity at the vital position of T45-R internal fluid was about 20% lower than that of GMF. The results of the velocity cloud diagram showed apparent high-velocity and low-velocity areas in the fish passage pipeline designed based on the T45-R Tesla valve. The high-velocity area was the vital position for fish upstream, and the maximum velocity variation range in this area was 0.904~1.478 m/s. At the same time, the flow in the low-velocity area is almost static water. The analysis illustrated that the resulting velocity environment could provide conditions for grass carp to move upstream successfully. The results of turbulent kinetic energy inside the fish passage pipeline showed that the maximum value of turbulent kinetic energy was only about 0.043 m²/s², which could be friendly for fish upstream. In addition, the results show that pressure-related problems could not seem to have an excessive impact on fish migration, such as causing damage. Overall, the results further studied the feasibility of using the Tesla valve as a fish passage pipeline.

Silt removal is crucial for maintaining navigable waterways in harbors. Jet pumps, without moving parts, are highly suitable for underwater operations such as channel dredging in port environments. Despite their structural advantages in slurry handling, the prolonged transport of solid–liquid two-phase flows can lead to wear on the wall materials, resulting in decreased efficiency and potential pump failure. The wear characteristics of the jet pump walls due to sand particles of varying grain sizes were experimentally investigated. The characteristic of the sands having a higher distribution above the axis as they enter the jet pump was captured by a high-speed camera. The experiment recorded the variations in mass loss at different sections of the jet pump over a period of 120 h, identifying that backflow within the throat region is a significant contributor to wall wear. Scanning electron microscopy was employed to examine the microstructure of the abraded pump surfaces. It was found that there are noticeable differences in the surface wear microstructure across various pump areas, and that particles of different grain sizes result in distinct wear patterns on the pump surfaces. The underlying causes of this phenomenon were discussed from the perspective of particle motion.

A large amount of primary energy is lost due to friction, and the study of new additive materials to improve friction performance is in line with the concept of low carbon. Carbon nanotubes (CNTs) have advantages in drag reduction and wear resistance with their hollow structure and self-lubricating properties. This review investigated the mechanism of improving friction properties of blocky composites (including polymer, metal, and ceramic-based composites) with CNTs’ incorporation. The characteristic tubular structure and the carbon film make low wear rate and friction coefficient on the surface. In addition, the effect of CNTs’ aggregation and interfacial bond strength on the wear resistance was analyzed. Within an appropriate concentration range of CNTs, the blocky composites exhibit better wear resistance properties. Based on the differences in drag reduction and wear resistance in different materials and preparation methods, further research directions of CNTs have been suggested.