Heng Qian

Steel gates are widely used in river and sea engineering to ensure water retention and flow regulation. Due to the attachment and the alternation of dry and wet environments, water retention easily causes corrosion and destruction, while the attachment is mainly cleaned manually at present. Based on stable adsorption, wall adaptability, and movement ability, a split four-track cleaning robot was developed. The split structure combined with a body swing and torsion mechanism can increase the degree of freedom of attitude adjustment and realize stable crawling of the curved panel. Considering the impact force of the water jet during cleaning, mechanical analysis of robot instability and driving torque on a curved surface was constructed to solve the problem of safe adsorption and flexible movement. A remote control system is constructed to complete the cleaning operation, and the coordination relationship between cleaning and crawling speed is analyzed. The performance test results show that the robot can crawl flexibly and stably on a curved surface, and the crawling speed can be greater than 0.052 m/s when the load is less than 5 kg. A continuous cleaning process has an obvious effect on silt and shellfish attachments, and the robot can meet the actual operational needs. The design process can help in the development of this kind of robot.

To investigate the variations in the flow field of centrifugal pumps with different cavitation numbers, this study utilized the shear stress transport k–ω turbulence model and Zwart–Gerber–Belamri cavitation model to examine the correlation between stall vortices and cavitation flow. The findings indicate that cavitation consistently coincides with the formation of stall vortices, and the distribution of cavitation mirrors the pattern of stall vortex structure. Cavitation tends to develop and aggregate around stall vortices, obstructing a significant portion of inlet areas within the flow channel. As the cavitation number decreases, both the area and intensity of stall vortices increase. For cavitations margins σ = 0.41, 0.23, and 0.15, we observed propagation frequencies of stall vortices at fs = 2.7, 1.8, and 0.9 Hz respectively, as these frequencies decrease relative to impeller movement until reaching near-stationary states. The pressure pulsations in various flow channels exhibit distinct phase differences; smaller cavity numbers result in larger phase disparities along with a gradual reduction in pressure pulsation amplitude. These discoveries present effective strategies for controlling and reducing both cavity formation and pressure fluctuations within centrifugal pumps, thereby enhancing overall stability.

To enhance the stability of photovoltaic power grid integration and improve power prediction accuracy, a photovoltaic power prediction method based on an improved snow ablation optimization algorithm (Good Point and Vibration Snow Ablation Optimizer, GVSAO) and Bi-directional Long Short-Term Memory (Bi-LSTM) network is proposed. Weather data is divided into three typical categories using K-means clustering, and data normalization is performed using the minmax method. The key structural parameters of Bi-LSTM, such as the feature dimension at each time step and the number of hidden units in each LSTM layer, are optimized based on the Good Point and Vibration strategy. A prediction model is constructed based on GVSAO-Bi-LSTM, and typical test functions are selected to analyze and evaluate the improved model. The research results show that the average absolute percentage error of the GVSAO-Bi-LSTM prediction model under sunny, cloudy, and rainy weather conditions are 4.75%, 5.41%, and 14.37%, respectively. Compared with other methods, the prediction results of this model are more accurate, verifying its effectiveness.

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.

The fundamentals of the design and operation of self-priming pumps, as indispensable equipment in industry, have been the focus of research in the field of fluid mechanics. This paper begins with a comprehensive background on self-priming pumps and gas-liquid two-phase flow, and it outlines recent advances in the field. Self-priming pumps within the gas-liquid two-phase flow state and the spatial and temporal evolution of the transient characteristics of self-priming pumps determine the self-priming pump self-absorption performance. Through mastery of the self-absorption mechanism, high-performance self-absorption pump products can be formed to provide theoretical support for the development of products. In current research, numerical simulation has become an important tool for analyzing and predicting the behavior of gas-liquid two-phase flow in self-priming pumps. This paper reviews existing numerical models of gas-liquid two-phase flow and categorizes them. Reviewing these models not only provides us with a comprehensive understanding of the existing research but also offers possible directions for future research. The complexity of gas–liquid interactions and their impact on pump performance is analyzed. Through these detailed discussions, we are able to identify the challenges in the simulation process and summarize what has been achieved. In order to further improve the accuracy and reliability of simulations, this paper introduces the latest simulation techniques and research methodologies, which provide new perspectives for a deeper understanding of gas-liquid two-phase flow. In addition, this paper investigates a variety of factors which affect the operating efficiency of self-priming pumps, including the design parameters, fluid properties, and operating conditions. Comprehensive consideration of these factors is crucial for optimizing pump performance. Finally, this paper summarizes the current research results and identifies the main findings and deficiencies. Based on this, the need to improve the accuracy of numerical simulations and to study the design parameters in depth to improve pump performance is emphasized.

The influence mechanism of the blade tip clearance (TC) of an inducer on the performance of a centrifugal pump at high speed was researched under different flow rate conditions in this work. An experiment on the pump’s external performance was carried out, and numerical calculation was also performed under four different TCs. The full characteristic performance curves, static pressure and pressure pulsation distributions of the pump were obtained. Through the research and analysis, it was found that the influence of the TC on the efficiency and the head of the centrifugal pump are related to the flow rate. Under the influence of a large flow rate, the increase in the TC is helpful to improve the efficiency and the head of the pump. The increase in the TC helps to weaken the gap jet effect on the inducer. The inlet jet of the inducer, caused by TC leakage, will form a low-pressure vortex zone at the inlet of the inducer. The splitter-bladed inducer’s pressure pulsation is affected by the TC. The peak pressure pulsation at the monitoring point at the short blades is larger than that at the long blades. With the increase in TC, the cavitation degree at the inlet of the long blade of the inducer is decreased, while the cavitation degree at the short blade is deepened. It is also found that the TC has little effect on the radial force of the inducer and the impeller. These results will provide the design basis for the tip clearance of an inducer.

In order to study the effect of tip clearance on the internal cavitation stability of a shunt blade inducer, an external characteristics experiment of a centrifugal pump with a shunt blade inducer was carried out. Based on the turbulence model and mixture model, the cavitating flow in a centrifugal pump with the inducer was numerically simulated. The influence of tip clearance on the cavitating flow in a shunt inducer was studied and analyzed. Through the research, it was found that tip clearance has a certain influence on the critical cavitation coefficient. The existence of the tip clearance caused a significant leakage vortex near the inducer’s inlet and a strong transient effect was shown. The location and degree of cavitation caused by the tip leakage are clarified in this paper. Tip clearance has a great impact on the pressure distribution on a shunt blade inducer. The influence law of tip clearance on an inducer’s blade load distribution was clarified. The results showed that tip clearance has a significant effect on the cavitation of a shunt blade inducer under low flow rate conditions.

The self-priming pump is a kind of centrifugal pump product with self-priming function, and the structural parameters of its reflux hole determine the performance. In order to reveal the mechanism of the self-priming process, we summarized the influence of structure parameters of the reflux hole on the performance of the self-priming pump. In this study, the transparent experimental pump was designed and manufactured, and a visual test bench was built. The gas–liquid two-phase flow pattern during the self-priming process with different reflux hole structure parameters was captured by high-speed camera. Results showed that: (1) the reflux hole of the self-priming pump affected the self-priming performance of the pump by affecting the backflow rate of the gas and liquid phases during the self-priming process. (2) Due to the uneven distribution of liquid velocity in the pump, the position of reflux hole had an obvious impact on the duration of self-priming middle stage, and the shortest duration was 13 s when φ = +15° and the longest duration was 45 s when φ = −30°. (3) The diameter of reflux hole had a very significant impact on the duration of the self-priming middle stage, and the shortest duration was 17 s when d = 10 mm and the longest duration was 94 s when d = 0 mm.

Self-priming pumps are widely used for irrigation, water treatments, and industrial areas due to the self-priming capacity. As we know, the gas-liquid flow pattern during the self-priming process is very complex and still not fully understood. In this study, a visualization test was performed to reveal gas-liquid two-phase flow patterns in a transparent pump during the self-priming process by using high-speed photography. The dynamic change of water column in the inlet-pipe and outlet-pipe was recorded by a digital camera, and the internal flow states of the test pump were recorded by a high-speed camera under different positions and different frame rates. First, the transient gas-liquid flow patterns during the self-priming process were revealed. In the initial stage, a large amount of gas was sucked into the impeller and the water level rose fast in the inlet pipe and then kept steady. With the increase in volume of gas in the impeller, plenty of bubbles were generated rapidly because of the mixing of gas and liquid inside the impeller. Some small bubbles were transported to the gas-liquid separation chamber by the centrifugal force, while rest of bubbles still circulated together with the impeller. In addition, the light gas was discharged to the outlet pipe and the heavy water was reserved inside the chamber due to the effect of gravity force. Afterwards, part of the water and gas flowed back to the impeller through the reflux hole. Second, the dynamic evolution of bubble formation was captured. Many bubbles appeared as the gas pocket was crushed by the blade surface or the jet flow. In general, the self-priming capacity was determined by the mixing rate of gas and liquid, the transporting rate of a gas-liquid mixture from the volute to the gas-liquid separation chamber, and the separating rate of gas from liquid.

In order to improve the working performance of the solid–liquid two-phase flow in centrifugal pump, the current study attempted to probe into the influence of the solid-phase particle concentration on the characteristics of centrifugal pump and the drag reduction characteristics of impeller on non-smooth surface. Based on the principle of bionics and with MP80-160 single-stage single-suction centrifugal pump as a model, the current study adopted Eulerian model to carry out numerical simulation by building the pit-type non-smooth surface on the impeller blades. The results show that the higher concentration of solid-phase particles leads to the more centrifugal pump hydraulic head and decreasing efficiency. The pit type in the layout of the non-smooth surface area shows a better drag reduction effect. Shear stress of wall inside the pit is much less than that on the smooth surface, which can effectively improve the working performance of the solid–liquid two-phase flow in centrifugal pump.