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Carbonate reservoirs worldwide are complex in structure, diverse in form, and highly heterogeneous. Based on these characteristics, the reservoir stimulation technologies and fluid flow characteristics of carbonate reservoirs are briefly described in this study. The development methods and EOR technologies of carbonate reservoirs are systematically summarized, the relevant mechanisms are analyzed, and the application status of oil fields is catalogued. The challenges in the development of carbonate reservoirs are discussed, and future research directions are explored. In the current development processes of carbonate reservoirs, water flooding and gas flooding remain the primary means but are often prone to channeling problems. Chemical flooding is an effective method of tertiary oil recovery, but the harsh formation conditions require high-performance chemical agents. The application of emerging technologies can enhance the oil recovery efficiency and environmental friendliness to a certain extent, which is welcome in hard-to-recover areas such as heavy oil reservoirs, but the economic cost is often high. In future research on EOR technologies, flow field control and flow channel plugging will be the potential directions of traditional development methods, and the application of nanoparticles will revolutionize the chemical EOR methods. On the basis of diversified reservoir stimulation, combined with a variety of modern data processing schemes, multichannel EOR technologies are being developed to realize the systematic, intelligent, and cost-effective development of carbonate reservoirs.

With the rapid growth of the global population and increasing pressures on freshwater resources, water scarcity has become one of the most pressing challenges worldwide. Agriculture accounts for approximately 70% of global freshwater consumption, making the efficient use of water in agricultural irrigation systems essential for sustainable water management. Irrigation valves, as key components in precision agricultural irrigation systems, critically influence the efficiency and reliability of water delivery through their hydraulic performance. This study presents a comprehensive quantitative review of the hydraulic characteristics and optimization of irrigation valves based on research published from 2005 to 2024, drawing from CNKI and Web of Science (WOS) databases. The review identifies research hotspots and evolving trends over time and systematically examines the evaluation indices used to assess hydraulic performance, including core parameters such as flow capacity, pressure loss, and cavitation, alongside important factors like noise, vibration, and sealing performance. Emphasizing advances in valve design, materials, and control methods, the analysis reveals that topological optimization has significantly enabled lightweight and efficient valve designs, composite coatings have greatly enhanced material durability, and optimized valve-closing strategies have effectively mitigated water hammer risks. The study concludes by outlining promising future directions for the hydraulic optimization of irrigation valves, aiming to provide valuable insights and reference points for ongoing and future research in water-efficient agricultural irrigation technologies.

Continuous water and sediment flow monitoring across river cross sections is essential for the management of flood- and sediment-related problems in watersheds. The sediment rating curve (SRC) estimates missing or uncertain sediment flow via its corresponding water discharge. Generally, a power form of relationship correlates the two quantities. The log-transformed water discharge and sediment discharge data were used to depict the SRCs developed in the present study. SRC parameter estimation via least squares regression using at-site dataset pairs can be found in the literature. However, the availability of reliable datasets at the site limits model applicability. This method does not describe the SRC on the basis of the continuity aspects of river system flow characteristics. Therefore, the current study proposes integrated SRC estimation models (Model 2 and Model 3) using modified Muskingum equations abiding by the spatial and temporal continuity of the entire river system state. These models are derived from streamflow storage balance criteria and ensure flow continuity norms. Moreover, Model 3 considers an inverse power form of the relationship depicting the water flow characteristics that govern the sediment transport phenomena through the river system. Standalone models for SRC parameter estimation (Model 1) were also developed for comparison among all three models via the root mean square error (RMSE), NRMSE (normalized root mean square error) and coefficient of determination (R2). The Mahanadi River system within Chhattisgarh state, India comprises five sections at tributaries, and the main channel was considered for the study. The improved NRMSE by Model 2 (7.53%) and Model 3 (7.14%) at Rajim and Model 3 (3.44%) at Bamnidhi in comparison to Model 1 at Rajim (9.19%) and Bamnidhi (4.80%) encouraged the application of integrated models for SRC estimation in river systems. Moreover, Model 3 outperformed Model 2 in some cases where the sediment transport process may be governed by water flow characteristics. [Display omitted] •Sediment rating curve estimate for entire river network replacing standalone model.•Muskingum model applications ensuring flow continuity, is recommended to adopt.•Water flow characteristics parameters influence sediment water relationship in river.•Both integrated models outperformed standalone model at upstream bounding section.

The internal flow scale of a Pelton turbine is variable, and the interaction between the jet and the bucket has strong transient characteristics, resulting in an incomplete understanding of its internal vortex structure evolution and energy dissipation mechanisms. In order to reveal the influence of vortices on the flow regime and energy dissipation mechanisms in the turbine, this paper establishes the correlation between the unsteady flow characteristics and energy dissipation inside the Pelton turbine based on the energy balance equation and quantifies the energy losses inside the turbine. The results indicate that vortex structures present a non-uniform distribution inside the jet, which disrupts the uniformity of the jet velocity distribution, resulting in an uneven distribution of high-vorticity zones on the bucket surfaces and intensifying flow interference among the buckets. The strong shear flow caused by the downstream flow detachment of the needle guide, the turbulent boundary layer on the jet surface, and the wake effect downstream of the needle tip are the main reasons for the dissipation of fluid kinetic energy. The distribution range of energy loss on the rotating bucket closely corresponds to the position of the high-vorticity zone. Energy dissipation inside the turbine is primarily in the form of turbulent kinetic energy, and the injectors and runner are the primary energy dissipation components. Moreover, inside the injectors, each form of energy loss remains relatively constant, whereas inside the runner, its rotation induces fluctuating energy losses attributed to Reynolds stress work. The results contribute to an enhanced understanding of the energy dissipation characteristics and complex flow mechanisms within the turbine, providing reference for the optimisation and efficient operation of the multi-nozzle Pelton turbine.

With the full construction of the South to North Water Diversion Project and the renovation of pumping stations, vertical axial flow pump devices have been widely used in various pumping station projects. This article uses the streamlined method to design the impeller and guide vanes of a vertical axial flow pump device. To analyze the hydraulic and structural characteristics, this paper uses CFD numerical simulation and fluid-structure interaction calculation methods. And the trend of output power change under different flow conditions was divided into three stages, elucidating the reasons for the sudden change in output power under flow conditions of 0.8 Q -1.0 Q . This article focuses on analyzing the internal flow state of the designed lower height guide vane segment to explore the problem of low guide vane height that is prone to occur during the design process. According to the research results, it is found that the lower height guide vane can also play a good role in stabilizing flow and recovering circulation under certain operating conditions. This article also studied the structural characteristics of the impeller and guide vanes, explaining the stress and strain distribution under design flow conditions.

Slurry pipeline transport, which is widely used in dredging, is an important method of solid material transportation. The internal structure information of flows with different shaped particles must be obtained to investigate the effects of different particle shapes on the efficiency and flow characteristics of slurry transport. To solve this problem, a numerical method which couples the computational fluid dynamics (CFD) and the discrete element method (DEM) is established in this study. Using the coupled CFD-DEM, the internal flow structure for spherical, square platens and line-shaped coarse particles is studied, and the working conditions under which clogging of non-spherical particles occurs are explored. The flow states of different shaped particles at velocities of 2, 4.1 and 8 ms−1 are qualitatively analyzed in a horizontal pipeline system within the diameter of 100 mm, and quantitative analyses of the concentration distribution in different flow regimes are performed. The study describes the particle flow characteristics under clogging conditions based on the flow regime transition and concentration distribution. Abnormal transport is analyzed using qualitative and quantitative indications. In addition, along with the particle force and robustness of transport, the conditions for stable transport are discussed.

In order to understand the transmission mode of laser in water jet–guided laser (WJGL) after entering blind holes, the flow characteristics of water jet in blind holes and the formation process of WJGL processing blind holes were studied. Firstly, the flow characteristics of water jets in blind holes under different water jet and blind hole conditions were studied through numerical simulation, including water jet diameter d (0–300 μm), hole diameter D (0–300 μm), and water jet velocity v (0–200 m/s). Secondly, single-point drilling experiments with different processing times (2–40 s) were conducted using WJGL technology to characterize the formation process of blind holes. Finally, the transmission mode of laser in blind holes and formation process mechanism of blind hole processed by WJGL were analyzed. The simulation results indicate that the process of water jet entering the blind hole can be divided into incident stage, rebound stage, and stable stage. The transmission of water jet in blind holes is influenced by D/d and v. When D/d is greater than 2.3, the water jet can stably transmit to the bottom of the blind hole. Taking 75 m/s and 150 m/s as the change points, as v increases, the stable transmission length of the water jet first decreases, then remains unchanged, and then increases. The experimental results indicate that with the increase of processing time, the formation process of blind holes undergoes rapid drilling stage, uniform reaming stage, bottom reaming stage, and stable stage. Under experimental conditions, the depth of blind holes first increases and then stabilizes with increasing processing time. The maximum depth of blind holes processed by WJGL is 720 μm. This article reveals the flow pattern of micro water jets in blind holes and the factors that affect their stable transmission for the first time. From the perspective of the guiding effect of water jets on laser, it is revealed that laser propagates along a straight line in a blind hole. The simulation and experimental results have guiding significance for improving the application of WJGL technology in blind hole processing.

IntroductionThe dimensionality of pedestrian infrastructure facilities have a great influence on pedestrian movements and a considerable impact on natural environment of the facility. Understanding the pedestrian movements are crucial to estimate the capacity of the system accurately, especially in the transportation terminals such as railway stations, bus terminals, airports and so forth, where large crowd gathers and transfers. To have a safe and comfortable movement in normal situation and also a quick evacuation in emergency situation, pedestrian movement patterns should be analysed and modelled properly.PurposeOnce the behaviour of pedestrians is established in terms of speed and density with respect to the environment, even for the colossal systems, the pedestrian flow characteristics can be modelled by applying extremely efficient simulations. The main modelling element in the context of flow models is the fundamental relationship among speed, flow and density. The objective of this study is to review the fundamental diagrams of pedestrian flow characteristics developed for various flow types and geometric elements. This paper also discusses the design values of flow parameters and walking speeds of pedestrians at various facilities.MethodsIn order to achieve the goal of this paper, we presented a systematic review of fundamental diagrams of pedestrian flow characteristics developed by using various approaches such as field, experimental and simulation.ConclusionsAfter a thorough review of literature, this paper identifies certain research gaps which provides an opportunity to enhance the understanding of fundamental diagrams of pedestrian flow characteristics.

To deeply investigate the internal flow characteristics of a Francis turbine under low-head conditions, this study takes a Francis turbine in a hydropower station as the research object. Based on the standard k-ω turbulence model, a full-flow passage numerical simulation was conducted to analyze the internal flow characteristics under different guide vane openings. The results show that at a 40% opening, the internal flow remains relatively stable, but the pressure gradient within the guide vanes undergoes the most significant variation, and the velocity vector distribution at the guide vane outlet is highly disordered. As the opening increases to 100%, a distinct low-pressure zone forms in the draft tube, exhibiting periodic variations over time. This leads to the generation of cavitation vortex ropes, which induce turbine vibrations and may significantly impact the normal operation of the hydroelectric generating unit.

MAXI J1535-571 outburst was dramatic and the accretion flow exhibits spectra-temporal characteristics related to one another. In this study, MAXI J1535-571 data observed by SWIFT/BAT (Swift/Burst Alert Telescope) and MAXI/GSC (Monitor of All-sky X-ray Image/Gas slit camera) was analyzed. The physical and phenomenological models that explain the components of the accretion flow were adopted in fitting/modelling the data in XSPEC v12.10.1f. The accretion flow characteristics and photon index–quasi-periodic oscillation frequency (Γ–vQPO) relation and their correlations were determined. The resonance condition in the range of (0.507–1.248) ± 0.080 indicates that the components of the accretion flow timescales are comparable. The QPO frequency of 0.840–4.961 Hz was obtained. This affirms the TCAF model prediction of the presence of QPO in the accretion flow during the hard spectral states. The components of accretion flow rates are anti-correlated. This suggests that components of the accretion flow interact at varying distances and cause the distribution of energy spectral indices in the post-shock region/Compton cloud. The photon index–QPO frequency is tightly correlated with a coefficient of 0.973. Hence, the variations/fluctuation of accretion flow/rates seems to be the underlying physical processes/mechanisms responsible for the origin of Γ–vQPO relation in the hard-intermediate spectral state.