Search Results (426)

The filling-and-emptying valve and downstream shaft are crucial components of navigation-lock systems. Under insufficient downstream submergence, air can be drawn through the shaft and trapped in the post-valve culvert, altering the flow structure and compromising hydraulic stability. A three-dimensional Reynolds-averaged Navier–Stokes/volume-of-fluid model was developed to investigate shaft aeration and entrapped-air-pocket evolution under varying inlet velocities and downstream-submergence depths. The aeration process comprises three stages: jet establishment, air-pocket formation, and air-pocket breakup and reorganization. Downstream-submergence depth determines whether a continuous air-intake pathway forms, whereas inlet velocity primarily controls aeration intensity and air-pocket persistence once the pathway is established. With decreasing submergence depth, the flow transitions successively from a water-sealed regime to a transition regime, a stable entrapped-air-pocket regime, and a strongly unsteady hydraulic-jump-like regime. For the present geometry and fixed valve opening, the transition from transient to sustained shaft aeration is identified within the downstream-submergence interval of h_w = 2–5 m. Combined analyses of the air-pocket volume per unit width, pressure response, vortex structures, and shear-layer characteristics indicate that enhanced jet-induced shear is closely associated with shaft aeration and air entrapment, while pressure fluctuations are closely coupled with air-pocket formation, persistence, breakup, and reorganization. Full article

In recent years, hydrogen-fueled internal combustion engines offer significant potential for achieving high efficiency and near-zero carbon emissions. However, stable combustion remains challenging due to the limited time available for fuel–air mixing, particularly in direct-injection concepts. This study investigates the influence of injector orientation on in-cylinder charge preparation in a heavy-duty spark-ignition engine operating with a side-mounted hydrogen direct-injection strategy. Three-dimensional computational fluid dynamics (CFD) simulations are performed to evaluate the effects of injector blow-cap inclination and azimuthal alignment on hydrogen jet evolution, flow-field development, and mixture formation. Under high-pressure injection conditions, hydrogen enters the cylinder as a highly under-expanded jet with strong momentum, resulting in significant interaction with the in-cylinder flow field. The results show that injector inclination influences jet impingement behavior, wall-guided flow development, and subsequent vortex evolution, while injector rotation modifies the interaction between the jet trajectory and in-cylinder swirl motion, affecting aerodynamic shear and flow-field complexity. The resulting mixture formation is evaluated through local air–fuel ratio distribution together with flow-field analysis and streamline evolution, demonstrating strong sensitivity to injector orientation and its coupling with in-cylinder aerodynamic structures. Quantitatively, injector orientation produces significant changes in the local air–fuel ratio distribution, with up to 25% reduction in the standard deviation of local air–fuel ratio for inclination variations and up to 35% for azimuthal variations between the extreme configurations, indicating improved mixture uniformity. Configurations promoting earlier jet disruption and enhanced spatial dispersion achieve more homogeneous charge preparation, whereas stronger wall-guided jet attachment results in localized fuel-rich regions. The findings provide physical insight into the role of jet–wall interaction, aerodynamic shear, and vortex restructuring in governing hydrogen mixing processes. The simulation framework captures the relevant in-cylinder flow physics and provides trends consistent with available experimental observations in the literature, which report improved efficiency and reduced NOx emissions under enhanced mixture homogeneity conditions. Full article

Due to system interactions, the formation and maintenance of dual squall lines are more complex than for single squall lines. In this study, we use upper-air soundings, ERA5 reanalysis data, high-density surface automatic weather station observations, and Doppler radar data to analyze a dual squall-line system that occurred over North China on 13 June 2022 under the Northeast China Cold Vortex. We focus on the differences between the two squall lines in mesoscale environments, convective triggering mechanisms, and maintenance processes. The main results are as follows: (1) The dual squall-line event occurred in different sectors of the Northeast China Cold Vortex, with both lines exhibiting a “dry-cold aloft, warm-moist below” stratification. However, significant spatiotemporal differences in mesoscale thermodynamic and dynamic conditions across Hebei and Shandong provinces led to distinct evolutionary pathways between the two squall lines. (2) Squall Line 1 (SL1) was triggered by the superposition of cold-pool outflow from convective cells over the Bohai Bay and convergence lines associated with surface cyclonic circulations. Squall Line 2 (SL2) was triggered by the thermal instability in the overlapping region of the temperature and dew-point fronts on the eastern slope of the Taihang Mountains, in conjunction with topographic uplift driven by the easterly flow. (3) This case study shows that squall-line maintenance depends not only on environmental CAPE and vertical wind shear but may also be closely related to the coordinated interplay between local thermal conditions and low-level shear. SL1, situated in a high-CAPE, low-LCL warm-moist environment, experienced relatively weak low-level shear; however, the ratio of cold-pool propagation speed to low-level shear remained near the RKW optimum, favoring persistence. Additionally, cold-pool spreading on the southern flank triggered new convection that merged into the southern end of the squall line, enhancing the cold pool via evaporative cooling and further promoting longevity. By contrast, SL2 displayed a pronounced north–south disparity: the northern segment failed to satisfy RKW balance due to insufficient cold-pool propagation relative to shear, leading to rapid echo dissipation; the southern segment, featuring an overly strong cold pool and low-CAPE, high-LCL conditions, inhibited deep convection. As a result, SL2 gradually split due to the spatial mismatch of thermodynamic and dynamic conditions along its north–south extent. Full article

Owing to its inherent flight safety, low takeoff and landing requirements, and favorable economic efficiency, the autogyro UAV, especially its electric and hybrid-electric variants, has become a core platform for low-altitude aviation missions such as transportation, inspection, and surveillance in plateau and offshore regions. However, the low air density and low Reynolds number conditions encountered in plateau regions can induce aerodynamic issues such as premature laminar flow separation, dynamic stall, and increased induced drag, which directly reduce payload capacity and endurance of small electric autogyro UAVs. In offshore environments, strong winds, turbulence, and gust disturbances intensify rotor–wake interactions, cause abrupt variations in aerodynamic loads, and reduce control margins, which severely restricts the mission reliability and flight safety of low-altitude unmanned platforms. These environmental effects collectively degrade rotor performance, including reduced aerodynamic efficiency and insufficient lift generation, and further amplify the energy constraint of electric/hybrid-electric propulsion systems. In response to bottlenecks that restrict the practical application of autogyro UAVs in extreme environments, this paper systematically reviews research progress on lift vector control for autogyro UAV rotors operating under such conditions. First, the typical aerodynamic problems encountered by autogyro UAVs in plateau and offshore environments are summarized, and their underlying physical mechanisms are analyzed from both system-level and local-flow perspectives, with a focus on how environmental factors affect the autorotation stability of unmanned platforms. Subsequently, the development of passive lift vector control technologies is reviewed, with an emphasis on the aerodynamic benefits of passive pitch mechanisms, vortex generators, and blade-tip winglets, as well as their engineering feasibility for small autogyro UAV blades. Active lift vector control technologies are then examined, including air-jet flow control, synthetic jets, and trailing-edge flaps, with discussions of their potential to delay flow separation and stall, enhance rotor aerodynamic efficiency, and an assessment of their adaptability to the energy and structural constraints of unmanned platforms. Finally, a lift vector control strategy suitable for autorotating rotors of autogyro UAVs is proposed, based on careful consideration of energy consumption, structural constraints, and control effectiveness. It provides a reference for aerodynamic optimization and flight control research on electric and hybrid-electric autogyro UAVs operating in extremely low-altitude environments. Full article

To overcome the limited dust control efficiency and backward dust diffusion tendency in fully mechanized excavation faces, this study pioneeringly proposes a wind-splitting dust control method based on a mechanical iris structure. This method actively splits and precisely allocates the airflow from the forced air duct outlet, achieving a synergistic effect between axial dust suppression and radial dust blocking. Through laboratory experiments and numerical simulations, the influences of the radial split ratio and the installation distance of the wind-splitting device on airflow and dust distribution were investigated. Results indicate that the proposed method significantly outperforms traditional ventilation. Optimal dust-control performance, considering both roadway-average concentration reduction and rear-area protection, was obtained at a radial split ratio of 0.6 and an installation distance of 24 m. Under these conditions, the axial-radial airflow and the exhaust negative pressure form a stable dust-blocking air curtain and a dust-controlling vortex in the front roadway, confining dust primarily within 6.4 m from the heading face. The average breathing zone dust concentration decreased to 22.62 mg/m³, and the roadway average dropped to 31.50 mg/m³, with a dust control efficiency of 77.56% and a significant reduction in rear dust concentrations. This offers effective ventilation optimization. Full article

In salt cavern compressed air energy storage (CAES) systems, slag particles entrained by high-pressure airflow can cause pipeline wear and flow instability, posing challenges to long-term operational safety. However, direct experimental studies are constrained by high-pressure, large-scale conditions and transient multiphase flow complexities. This study uses Fluent, a numerical simulation method based on gas–solid two-phase flow theory, to investigate the flow characteristics, particle dynamics, and erosion behavior in the above-ground pipeline of CAES system. Results reveal uneven gas velocity distribution, with the lowest flow (≤2.3 (m/s)) in the main pipeline favoring particle deposition, and complex vortex structures at branch connections. Particles accumulate on the outer wall of 90° elbows due to centrifugal effects, leading to localized erosion, with severe wear occurring at impact angles of 20–30°. Over a 30-year operational cycle, the predicted maximum wear depth is 0.38 mm, which remains below the existing protective cladding thickness of 0.5 mm. The findings not only provide a theoretical basis and design insights for optimizing wear protection strategies, but also hold positive implications for enhancing the economic sustainability and environmental benefits of large-scale energy storage systems. Full article

The rapid melting of Arctic sea ice has significantly lengthened the window for Northeast Passage navigation, but the frequent occurrence of accompanying extreme weather events poses severe challenges to shipping safety. Based on 1991–2020 climate data and 2021–2024 NCEP reanalysis data, this study uses wave activity flux diagnosis, composite analysis and statistical test methods to reveal the causes of abnormal circulation and the energy propagation mechanism of heavy precipitation events during the navigation period (July–October) in the starting section of the Arctic Northeast Passage (from the Barents to the Kara Sea). The results show that from 2021 to 2024, there was a high proportion of heavy precipitation events during the navigation period (July–October), with significant temporal and spatial variability; abnormal circulation is triggered by the synergistic effect of the eastward shift in the Ural blocking high and the southward extension of the Arctic polar vortex. The enhanced upper-level westerly jet and the mid-level “tripole-type” teleconnection wave drive jointly drive the northward transport of warm, moist air, and the low-level cyclonic circulation and upper-level divergence trigger a baroclinic lifting mechanism. Rossby wave energy originates from the Mediterranean–Black Sea region, propagating eastward to the study area along the jet axis and enhancing the ascending motion through wave activity flux divergence. The heavy precipitation event in August 2023 is a typical example of the cross-seasonal synergistic sea temperature–sea ice–atmosphere effect. This study reveals the following complete teleconnection chain: “sea temperature anomaly → wave train excitation → sea ice feedback → circulation maintenance”, which will support predicting disastrous weather and developing climate adaptation strategies in the Arctic Passage. Full article

Air-assist atomization exploits high-velocity gas streams to shear liquid phases, achieving fine droplets at supply pressures significantly lower than those required by conventional pressure atomization. This technology is extensively deployed across diverse sectors, including pesticide spraying, food spray drying, sanitization/disinfection, and combustion atomization. Although specific operational fields dictate vastly contrasting droplet size distributions, velocities, and deposition uniformities—with target diameters spanning from <50 μm to >200 μm—their foundational atomization mechanisms remain inherently unified, governed primarily by toroidal vortex-induced primary breakup and Kelvin–Helmholtz/Rayleigh–Taylor (KH–RT) or Taylor Analogy Breakup (TAB) secondary breakup. This review systematically parses the atomization mechanisms, critical performance metrics, numerical simulation frameworks, and experimental characterization methodologies of air-assist nozzles. Crucially, from a novel “cross-disciplinary custom design” perspective, we contrast the optimal droplet parameter windows across the agricultural, food, sanitization, and combustion sectors (e.g., electrostatic plant protection yields a 203–1350% increase in abaxial leaf deposition; mine wind-assisted misting achieves a >90% collection efficiency for PM₁₀ dust; and SCR air-assisted injectors reduce the Sauter Mean Diameter (SMD) to 25 μm). Synthesized insights reveal that segmented VOF-to-DPM transition frameworks, corner-vortex-induced breakup theories, and closed-loop adaptive control architectures possess substantial cross-domain migration value. Current bottleneck challenges are highlighted, including the mesh dependency of droplet collision–coalescence models in dense spray regimes, the absence of robust atomization constitutive formulations for non-Newtonian fluids, and the ongoing paradigm shift from open-loop presetting to intelligent closed-loop regulation. This work establishes a comprehensive theoretical foundation and technical roadmap for cross-disciplinary integration and next-generation smart nozzle design in air-assist atomization. Full article

The dynamic evolution of an optically induced vortex flow in nematic microliter droplets caused by exposure to a focused laser beam has been studied both experimentally using polarized optical microscopy and numerically within the framework of a corresponding nonlinear extension of the Ericksen–Leslie theory supplemented by thermomechanical correction of the stress tensor and the entropy balance equation. The vortex flow in nematic droplets consisting of 4-pentyl-4′-cyanobiphenyl molecules spreading over the functionalized surface was visualized in microliter droplets doped with monodisperse polystyrene tracers, under exposure to a laser beam with an optical power equal to 8.0 mW. Using the computer vision detection algorithm, we have identified radial symmetry in the tracers motion, where comet-like tracks are aligned along the rays emanating from the center of the resulting structure. At the same time, some of the “comets” are flying towards the center, while others are moving away from it. This allowed us to estimated the average value of tracer flows, which is of 17 µm/s. All these observations indicate that vortex currents are excited in the droplet under the action of the focused laser beam. The nature of thermally excited vortex flows in the microliter hybrid aligned nematic droplet with a free upper LC/air interface and spreading over the solid surface under the influence of the heat flux directed through the lower bounding surface is also numerically investigated. It was shown that due to the interaction between $\nabla T$ and the gradient of the director field $\nabla \widehat{\mathbf{n}}$, the thermally driven bi-vortical flow is maintained in nematic microvolume. Full article

The lubrication performance of high-speed transmission systems directly affects mechanical power consumption and operational reliability. During high-speed oil-stirring lubrication, strong gas–liquid interfacial shear, liquid-film deformation, droplet splashing, and oil-mist transport generate an unsteady multiphase turbulent flow field. Conventional continuum-based numerical methods often face difficulties in resolving interface breakup and transient turbulent dissipation under high-speed rotational excitation. To address this problem, this study develops a coupled Lattice Boltzmann–Large Eddy Simulation (LBM–LES) method for oil–air two-phase flow in a high-speed oil-stirring lubrication system. The D3Q27 discrete velocity model, cumulant collision operator, WALE subgrid-scale model, free-surface tracking, and local grid refinement are integrated to analyze free-surface deformation, oil-mist evolution, and power-loss characteristics. Taking a notched toothless oil-stirring disk as the reference configuration, the effects of oil immersion depth and disk topology on gas–liquid phase distribution, oil-mist coverage, power consumption, and vortex-induced energy dissipation are investigated. The results indicate that oil immersion depth has a nonlinear influence on lubrication performance and power loss. Among the investigated cases, an immersion depth of 20 mm provides a favorable balance between upper-region oil-mist coverage and lower-region oil-pool stability. At this depth, the notched disk exhibits directional oil delivery and relatively low power consumption, whereas the double-rhombus structure expands the oil-mist coverage but increases the average power consumption to approximately 175 W. These findings provide numerical support for balancing oil-mist coverage, mechanical power consumption, and disk topology design in high-speed transmission lubrication systems. Full article

In this study, a sustainable advanced manufacturing technology was developed using a holistic approach for finishing heat-treated 42CrMo4 steel cylindrical parts. The proposed technology is based on a hybrid combined process (HCP) involving cool-assisted dry hard turning and subsequent cool-assisted dry diamond burnishing (DB). A cold-air cooling (without lubrication) condition was achieved using a special device with a cold-air nozzle based on the principle of vortex tubes. The study was conducted in two stages. In the first stage, only the hard turning process was investigated using variance analysis to determine the significant governing factors (feed rate and cutting insert radius). The second stage involved studying and optimising the HCP. This approach incorporated the two significant turning process factors, along with three additional DB process factors: the radius of the diamond insert, burnishing force and feed rate. The selected objective functions were the average roughness, skewness, kurtosis, surface microhardness, residual surface axial stress and fatigue limit. The fatigue limit was determined using the accelerated Locati method. Mathematical models of the objective functions were obtained using experiments and regression analyses. Using multi-objective optimisation, the HCP was optimised based on two criteria: (1) maximum wear resistance under boundary lubrication conditions and (2) maximum fatigue limit. The optimisation tasks were solved by searching for the Pareto optimal solution approach using QStatLab and the NSGA II algorithm. The compromise optimal values of the governing factors, maximising the fatigue limit (690 MPa), are as follows: feed rate in turning and DB of 0.05 mm/rev, radius of the cutting insert of 0.8 mm, diamond insert radius of 2 mm, and burnishing force of 50 N. Experimental verification showed a good agreement with the optimised solutions for surface integrity and fatigue limit characteristics. Full article

Understanding which structural parameters govern flow stability and particle separation is essential for turbo air classifier design. In this study, the Y160L-6 turbo air classifier was used to examine whether different categories of spatial structural parameters influence classification performance through the same flow mechanism or play distinct roles in regulating the internal flow field. Two representative parameters, namely the spacing between the secondary air inlet and the rotor cage and the spacing between the secondary air inlet and the feed inlet, were analyzed using computational fluid dynamics (CFD) coupled with the RNG k–ε turbulence model and the discrete phase model (DPM). The results show that the two parameters affect the classifier through different mechanisms. Increasing the secondary air inlet–rotor cage spacing causes a non-monotonic variation in wall pressure and tangential velocity, indicating a strong influence on the global swirling structure. At a spacing of 1490 mm, the pressure distribution in the classification zone becomes more uniform, the tangential velocity reaches a relatively high level, and the intensity of the precessing vortex core (PVC) is reduced. Under this condition, the cumulative proportion of 2–5 μm particles at the fine powder outlet increases by 34.1% compared with the initial configuration. In contrast, variations in the secondary air inlet–feed inlet spacing exert only a limited influence on the overall flow structure and classification characteristics under relatively low feed inlet velocity conditions, indicating that this parameter mainly affects local flow disturbance rather than global flow stability. These findings demonstrate that structural parameters associated with the coupling between secondary airflow and rotor rotation dominate classifier performance, whereas parameters related to feed–air interaction exert only a secondary effect under low feed momentum conditions. These findings provide design guidance for the investigated Y160L-6 turbo air classifier and may serve as a reference for similar classifier structures under comparable operating conditions. Full article

Based on the Multi-Sensor Reanalysis Version 2 (MSR-2) and ERA5 datasets, variations in monthly mean total ozone column (TOC) over Northeast China (40–53°N, 115–135°E) from 2015 to 2024 are analyzed. Local ground-based observations at the regional WMO/GAW Longfengshan Station are also used. The aim is to investigate regional seasonality in TOC pattern and the relationship between TOC and ozone concentration and air temperature in the stratosphere and at the surface. No statistically significant linear trend was found for TOC; however, the annual mean TOC in the study region exceeds the zonal mean TOC by 25 DU (7.4%), and the annual maximum in February and minimum in August are observed one and two months earlier, respectively, than in the Northern Hemisphere mid-latitudes. A climatological decrease in TOC from the northeastern (~415 DU) to southwestern (~330 DU) parts of Northeast China was found. We also found a strong correlation, approaching |r| = 0.8–0.9, between TOC and ozone concentration (positive) and temperature (negative) at the surface. The time series from Longfengshan Station for 2015–2022 closely match the MSR-2 data averaged over Northeast China: the monthly mean difference varies within ±15 DU (±4.2%), validating the reliability of the station data as a representative proxy for regional TOC variability. The role of the Brewer–Dobson circulation, quasi-stationary waves, and the Northeast China cold vortex in the detected patterns and quantitative associations of TOC is discussed. The findings of this work can be applied to analyze the ozone observations, TOC variability, and stratosphere–troposphere coupling in East Asia. Full article

The internal flow of a semi-open axial flow fan is highly three-dimensional and unsteady due to the absence of a confined passage. The evolution of complex vortical structures, such as the tip leakage vortex (TLV) and corner separation vortex (CSV), remains poorly understood. This study used high-resolution particle image velocimetry (PIV) to conduct multi-region, multi-view measurements of the flow field in a semi-open fan for an outdoor air conditioning unit. The generation, development, and breakdown of the TLV were analyzed, revealing transient nonuniform flow and wake evolution. Dynamic mode decomposition (DMD) was applied to extract dominant frequencies and spatial modes. The results show that the TLV has a dominant frequency of 98.5 Hz (2.19 times the rotational frequency), accounting for 88.5% of the total energy, and exhibits periodic shedding and asymmetric breakdown. The CSV dominates at 16.44 Hz, slightly above blade rotation, and interacts with the TLV. In the wake region, the dominant frequency is 248.45 Hz, arising from the nonlinear superposition of TLV harmonics, the CSV frequency, and the blade passing frequency. This study provides an experimental basis and a low-dimensional coherent structure model for internal flow diagnostics and the structural optimization of semi-open axial flow fans. Full article

To protect human health and the environment, it is necessary to reduce the number of solid particles and harmful gases in the air or to minimize such pollution. Filtration and separation devices are intended for various industrial operations to capture pollutants from various technological processes. In the introduction, this article points out the use of cyclone filters in individual operations, names the most frequently occurring elements of pollution, and suggests the most suitable method of separation. In paint shops, grinding shops, welding workplaces, machining lines, and when handling powder materials, particles with very different properties are created. An important advantage of using cyclone filters is not only their simple construction but also their usability at high temperatures and pressures. Furthermore, this article highlights that cyclones are easy to maintain, typically contain no moving parts, are simple to manufacture, and are cost-effective, particularly as pre-filtration devices. Their efficiency generally ranges from 50% to 99% and is strongly influenced by design and operating parameters, especially cyclone geometry, which affects pressure drop, flow structure, cut diameter, and fractional collection efficiency. The article also summarizes that various modifications of the inlet, vortex finder, outlet pipe, and cyclone body have been proposed to enhance separation performance, particularly for smaller particles. Nevertheless, due to the centrifugal and inertial nature of cyclone separation, fine and submicrometric particulate matter remains difficult to remove using cyclones alone. Fabric filters are also analyzed as a possible solution, but high loading by coarse particles may cause clogging, increased pressure drop, and higher maintenance costs. In the end, the combination of a cyclone with an electrostatic precipitator is presented as a staged separation approach, enabling efficient removal of both coarse particles and fine particulate matter from the gas stream. Full article