Search Results (934)

When predicting cavitation erosion risk in practical engineering bearings, traditional vapor cavitation models neglect the effect of dissolved air in the lubricant and fail to account for its precipitation and dynamic evolution in local low-pressure regions, leading to deviations in the prediction of cavitation extent, intensity, and distribution. Taking the main bearing of a certain type of diesel engine as the research object, a coupled cavitation model combining the Schnerr–Sauer vapor cavitation model and a Henry’s law-based gas dissolution model is established. Together with large eddy simulation (LES), the accuracy of the numerical model is verified by constructing a visualization experimental platform. Numerical analysis is then carried out to investigate the effect of dissolved air in the lubricant on the cavitating flow field of the bearing oil film under initial conditions ranging from undersaturated to saturated states (air mass concentration of 0–0.4 g/L). The results show that as the mass concentration increases, the amount of air precipitation in the near-wall region gradually increases and extends downstream. When the mass concentration reaches 0.1 g/L, the precipitated air mass reaches 50% of the vapor cavitation mass, significantly expanding the cavitation range. In the critical mass concentration range of 0.24–0.28 g/L, intense air precipitation occurs inside the oil hole and covers the entire region. Through the synergistic effects of inhibiting high-speed jets, altering the local pressure field, and competing for cavitation nuclei, the precipitated air significantly suppresses the development of near-wall vapor cavitation, and the vapor cavitation mass decreases by 83.1% at saturation. In summary, within the practical mass concentration range, the presence of dissolved air significantly enhances the gas phase intensity near the bearing bush surface and expands the cavitation range, thereby exacerbating the risk of cavitation erosion damage in this region, while having little effect on the oil supply performance of the oil hole. Full article

Clarifying combustion-space behavior is essential for operating large-tonnage natural gas-fired float glass furnaces with complex single-furnace dual-cooler layouts. In this study, a three-dimensional computational fluid dynamics model of the gas-phase combustion space of a 1300 t/d natural gas-fired float glass furnace was developed and validated using crown-temperature measurements, with a maximum relative error of 3.3%. The effects of burner inclination angle (β = 5°, 10°, and 15°) and excess air ratio (α = 1.0–1.20) on temperature distribution, flame morphology, and flue-gas recirculation were investigated. The results show that β = 5° produces a more horizontally extended natural-gas jet, enhances contact with preheated air, and forms a wider high-temperature region, with a maximum temperature of 2512 K. Increasing the excess air ratio improves combustion completeness and enlarges the high-temperature region; however, further increasing α from 1.15 to 1.20 provides only marginal thermal benefits while increasing sensible heat loss through the exhaust gas. Among the investigated operating conditions, β = 5° and α = 1.15 achieve the lowest outlet flue-gas specific enthalpy of 755 KJ/Kg. Full article

The cavitation jet is regarded as a promising hydraulic rock-breaking technique for drilling and exploiting deep-sea natural gas hydrate (NGH). However, the detailed mechanisms of erosion pit formation in hydrate-bearing sediments (HBSs) under cavitation jet erosion remain unclear, and effective simulation methods are still limited. This study first conducts jet erosion experiments on HBSs using a convergent–divergent cavitation jet nozzle (CDCJ) and a conical jet (CJ) nozzle to evaluate the erosion performance of the CDCJ. The CDCJ is then applied to erode HBS specimens under different flow rates, erosion times, and stand-off distances, with the geometric characteristics of the erosion pits recorded. Subsequently, a coupled CFD-DEM framework is developed to further investigate the erosion process and mechanisms. Based on this model, the erosion characteristics of the cavitation jet at different stages and under varying jet parameters are analyzed and validated. The results show that the CDCJ exhibits a significantly stronger erosion capacity than the CJ, with the pit volume and depth reaching 1.36 and 1.19 times those produced by the CJ, respectively. The hole-forming process induced by the cavitation jet can be divided into three stages: the V-shaped hole-forming stage, the cylindrical hole-forming stage, and the spindle-shaped hole-forming stage. In the V-shaped hole-forming stage, jet impingement and the penetrating erosion of cavitation clouds dominate pit development. As erosion progresses, the axial impingement gradually weakens, whereas radial cutting decays more slowly. Meanwhile, vortices inside the pit trap cavitation clouds and promote further hole enlargement. Both the experiments and simulations indicate that higher flow rates produce larger and deeper pits, and a standoff distance of 5 mm is optimal for cavitation erosion. These findings clarify the hole-forming mechanism and flow-field evolution during the cavitation erosion of HBSs, and provide guidance for the application of the cavitation jet in NGH drilling and exploitation. Full article

This study investigates heat transfer enhancement in the cooling channels of gas turbine blade turbulators using modified transverse baffles with isosceles triangular sawtooth perforations. The proposed baffle design aims to improve convective heat transfer by promoting flow mixing and disrupting the thermal boundary layer. Experiments were conducted in a rectangular channel with an aspect ratio of 3.75 under constant heat flux conditions using air (Pr = 0.7) as the working fluid. The effects of Reynolds number (Re = 6000–24,000), sawtooth width ratio (a/W = 0.0, 0.0625, 0.125, 0.25, and 0.5), and sawtooth height ratio (b/e = 0.0, 0.25, 0.5, 0.75, and 1.0) were systematically investigated. The blockage ratio (e/H) and pitch ratio (P/H) were maintained at 0.3 and 1.5, respectively. Heat transfer characteristics were evaluated using the thermochromic liquid crystal (TLC) technique, while thermal–hydraulic performance was assessed in terms of the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). The results demonstrate that introducing sawtooth perforations significantly enhances heat transfer compared with a smooth channel, yielding Nusselt number ratios (Nu/Nu_s) between 1.6 and 2.6. The highest heat transfer enhancement was achieved at a/W = 0.0625 and b/e = 0.25, where the relatively small sawtooth openings generated stronger jet impingement, enhanced flow mixing, and more effective disruption of the thermal boundary layer. However, these geometric modifications also increased the pressure loss due to intensified flow blockage and recirculation, resulting in friction factor ratios (f/f_s) ranging from 8.9 to 14.9. The maximum pressure-drop penalty occurred at b/e = 0.25 because the smaller openings produced stronger turbulence and increased flow resistance. Despite the increased friction loss, the optimum configuration (a/W = 0.0625 and b/e = 0.25) achieved the highest thermal performance factor of 1.2 at Re = 6000. Full article

Reliable discharge of bulk granular materials is essential for the efficient operation of shaft furnaces, pneumatic conveying systems, and industrial dosing equipment, where uncontrolled arch formation can lead to flow instability and blockage. This study investigates the effect of gas velocity, direction, and configuration on arch formation and collapse during bulk granular material discharge through horizontal orifices. Experiments were conducted using cold quasi-2D (250 × 50 × 5 mm) and hot scale models (cylindrical shaft, D = 300 mm, H = 500 mm) with high-speed imaging (2000 fps, 1280 × 1024) across various materials. Uniform gas flow stabilizes arches, reducing the normalized mass flow rate $W_t/W_0$ to 0.20 ± 0.03 at critical gas velocity ratios $V_1/V_2\le 20$ and area ratios $L_1/L_2\ge 0.37.$ Conversely, localized gas jets increase $W_t/W_0$ to 1.45 ± 0.05. The scientific novelty lies in the development of a unified torque-balance model that, for the first time, predicts critical counter-current gas velocities $V_{kr}$ across different operating configurations with an error not exceeding ±28.9% (n = 3, p < 0.05). Three characteristic discharge regimes—continuous flow, pulsating discharge, and blockage-dominated flow—were identified and related to the stability of dynamically unstable arch structures. These findings provide a quantitative basis for the design and optimization of industrial systems such as shaft furnaces, pneumatic conveyors, and dosing units. Future work will focus on industrial-scale validation, extension to humid or cohesive materials, and investigation of more complex flow geometries to further improve gas-assisted flow control. Full article

In the process of oil and gas drilling, the blowout preventer (BOP) serves as the last line of defense before wellhead loss of control, and its sealing reliability is of critical importance. However, under the erosion of high-pressure sand-containing fluids, the sealing components of the BOP are prone to failure, resulting in long-slit-type leakage ports, which seriously threaten well control safety. In response to the current lack of theoretical guidance for emergency plugging process parameters, this paper adopts the coupled computational fluid dynamics and discrete element method (CFD-DEM) to establish a numerical model for the plugging of long-slit-type gaps with particles under blowout conditions. The migration and bridging plugging behaviors of three typical shaped particles, namely spherical, cylindrical, and square, under different sizes, concentrations, and pump injection rates are systematically studied. The results indicate that particle transport within the wellbore can be divided into an initial transport stage dominated by jet diffusion and a plugging-structure formation stage dominated by bridging and particle accumulation. When the particle size exceeds the slit width, cylindrical particles exhibit comparatively better plugging performance under the conditions considered in this study. For a long-slit leakage channel with a width of 5 mm, the combination of cylindrical particles with an equivalent diameter of 6 mm, a particle volume concentration of 20%, and a pumping rate of 2.4 m³/min demonstrated relatively favorable overall plugging performance. The particle concentration mainly affects the bridging time, and the bridging time tends to stabilize when the concentration reaches 20%. The higher the pump injection rate, the earlier the particles reach the gap opening, but it has little impact on the final plugging effect. This study provides a scientific basis for the optimization of emergency plugging process parameters after BOP sealing failure, filling the gap in the research on the plugging mechanism of equipment leakage under blowout conditions. Full article

The complex behavior of multi-scale droplets in Hydro-jet Cyclone (HJC) systems constrains the parametric study of gas–liquid separation and interfacial transfer. To investigate droplet dynamics at a specific scale in swirling flows, this study employed 500-μm simulated droplet particles (SDPs) and examined the effects of inlet gas rate, column height, and cone angle on trajectories, revolution speed, and self-rotation speed using the Computational Fluid Dynamics-Discrete Phase Model (CFD-DPM). The results demonstrate that SDPs exhibit suspended circulation within the cyclone. The suspension zone expands toward the overflow pipe with increasing gas rate and cone angle, but migrates downward with increasing column height. The revolution speed increases from about 50 rad/s to 80 rad/s as inlet gas rate rises, but decays with increasing column height, while cone angle has little influence. The self-rotation speed is driven by near-wall shear, reaching an instantaneous peak of 4500 rad/s at the inlet; after stable suspension, it increases markedly with gas rate, from <3500 rad/s at 12 m/s to 12,000 rad/s at 22 m/s. Inlet gas rate is the dominant factor governing self-rotation, followed by cone angle, whereas column height mainly affects suspension position. This study provides a numerical reference for droplet dynamics in HJC gas–liquid systems. Full article

Wellbore plugging has become the primary constraint on gas production for numerous oil, gas, and geothermal wells in China. To enhance productivity in mature wells, a novel straight-swirling integrated jet (SSIJ) deplugging tool was designed, incorporating a converging-diverging jet (CDJ) nozzle. A combined approach of numerical simulation and experiments was employed to optimize the tool structure and evaluate the effects of different operational parameters on its blockage-removal performance. Structural optimization identified an impeller spinning angle of 540° and an impeller thickness of 12 mm as the optimal parameters, which significantly improve the three-dimensional velocity peaks and cavitation generation capability. Compared with the CDJ nozzle, the SSIJ tool produces substantially higher tangential and radial velocity components, with peak tangential and radial velocities reaching 22 m/s and 45 m/s, respectively, under the optimized conditions. The numerical results show that the peak impact pressure reaches 2.7 MPa at a standoff distance of 12 mm, while the optimal standoff distance, considering both impact magnitude and effective coverage area, is determined to be 16 mm (4 times the outlet diameter). Furthermore, indoor validation experiments under a pump pressure of 20 MPa demonstrate that the tool completely removes the artificial scale layer from the tubing inner wall within 2 min of continuous flushing, leaving no visible residue. This study provides a quantitative reference for the design and process optimization of jet blockage-removal tools. Full article

Growing interest in transporting hydrogen via natural gas pipelines highlights the need to understand flame characteristics during accidental leakage. However, limited literature is available on addressing the flame horizontal projection length of hydrogen-blended natural gas jet fires under inclined conditions. Therefore, a series of experiments was conducted to investigate inclined H₂/CH₄ jet fires, with methane used as a surrogate for natural gas. Experiments with hydrogen content ranging from 0% to 20% were performed to examine the effects of inclination angle (0°, 30°, 45°, 60°, and 90°), nozzle diameter (2, 3, and 4 mm), and gas flow rate (4–25 L/min) on the flame morphological characteristics. It was found that the flame color evolves from a transparent blue base to a yellow luminous tip with increasing hydrogen content or fuel exit velocity, accompanied by soot enrichment in the luminous region. The flame horizontal projection length was quantified under different conditions. Results show it is only slightly affected when the hydrogen content is below 20%, whereas it increases with fuel exit velocity and nozzle diameter, and decreases with inclination angle. An explicit model was proposed by introducing the dimensionless heat release rate (${\dot{Q}}^{*}$), which predicts the flame horizontal projection length with good agreement with experimental data. The findings provide a basis for the safety design and risk assessment of hydrogen-blended natural gas pipelines. Full article

The increasing global demand for marine energy resources, coupled with the deployment of offshore oil and gas pipelines and submarine power cables, highlights the requirement for reliable subsea infrastructure. To protect these assets from environmental hazards and anthropogenic disturbances, seabed burial via trenching is widely adopted, with submarine trenchers serving as the main installation equipment. Trenching involves excavating a trench on the seabed to place pipelines, cables, or other subsea infrastructure. These operations involve complex soil–tool interactions that fundamentally govern cutting resistance, trench-wall stability, and overall equipment performance. Specifically, distinct engineering challenges arise across different trencher configurations: plough trenchers often encounter complex seabed structures, jet-type trenchers are prone to trench sidewall collapse, and mechanical trenchers face cutting difficulties in hard clay. A thorough understanding of these interactions is therefore critical for resolving operational challenges and optimizing trencher efficiency in engineering practice. To deeply understand these type-specific issues, this review summarizes the geomechanical problems associated with various trenching technologies, synthesizes recent research advances from analytical frameworks, physical experiments, and numerical simulations, and identifies existing knowledge gaps. By consolidating these findings, the paper provides a reference for addressing trencher-related engineering challenges, supporting equipment optimization, and facilitating the deployment of offshore energy transmission networks. Full article

The development of low-emission and reliable propulsion systems is essential for extending the operational capability of unmanned aerial vehicles (UAVs). Although aviation decarbonization is widely recognized as an important objective, it must be considered within the broader context of limited renewable-energy availability. Recent system-level analyses of transportation decarbonization have shown that the allocation of renewable electricity and sustainable fuels should prioritize sectors where direct electrification is most efficient, while hard-to-electrify sectors require alternative pathways. Aviation is one of the most difficult transport sectors to electrify because of strict energy-density requirements, especially for long-endurance airborne platforms. Therefore, sustainable liquid fuels and hybrid propulsion systems should not be considered universal replacements for electrification, but rather complementary solutions for applications where batteries alone cannot provide the required endurance, payload capacity or operational flexibility. In this context, the present study focuses on alcohol–kerosene blends for hybrid UAV power systems, where liquid-fuel energy density and partial emission reduction remain relevant engineering requirements. This work provides one of the first systematic experimental evaluations of ethanol–, butanol– and octanol–kerosene blends in a micro-turboprop engine operating as part of a hybrid UAV power-generation architecture. Unlike previous studies focused mainly on micro-turbojet thrust response, the present work evaluates the coupled influence of alcohol chain length and blending ratio on exhaust gas temperature, gaseous emissions, electrical output and operational stability under multi-load conditions representative of UAV operation. Jet-A and nine alcohol–kerosene blends containing 10%, 20% and 30% ethanol, butanol or octanol by volume were tested over four operating regimes, from idle to 2500 W electrical load. The results show that ethanol blends provided the strongest CO reduction, with E30 reducing CO by 24.9% relative to Jet-A under R3, while E10 offered the most balanced behavior across the full operating range. Higher ethanol fractions improved CO suppression but introduced NOx and low-load stability penalties. Octanol blends, particularly O20, exhibited the most kerosene-like and stable response, supporting reliable power delivery with reduced operational variability. Butanol blends showed intermediate behavior without providing a dominant advantage. A multi-criteria evaluation combining emissions, EGT behavior, relative performance, operational stability and cost identified E10 as the best overall compromise for hybrid UAV use. The study demonstrates that alcohol chain length produces nonlinear system-level effects in hybrid micro-turboprop architectures and provides an experimental basis for fuel selection in low-emission UAV power systems. Full article

In this work, Direct Numerical Simulation (DNS) investigates the combustion behaviour of a reactive transverse lean premixed jet of an ammonia blend (10% NH₃, 11% H₂, 16% O₂ and 63% N₂ by volume) injected through a rectangular nozzle in a pre-heated non-vitiated air crossflow at a pressure of 5 bar. The configuration has been chosen from a Reynolds-Averaged Navier–Stokes (RANS) test campaign to ensure low NO and low unburned fuel, while maintaining a high temperature profile at the turbine inlet. The DNS shows that the flame stabilises on the leeward side of the rectangular jet, within and downstream of the recirculation region, while high scalar dissipation and short residence times prevent persistent anchoring on the windward side. Joint statistics reveal that the reaction does not follow a constant equivalence ratio path, since intermediate progress states are shifted towards leaner mixtures by entrainment, dilution and differential diffusion. The strongest heat-release and displacement-speed events occur in localised regions where mixture state, stretch and flame-front geometry act jointly. The displacement-speed budget is mainly controlled by the chemical source term, with diffusion reducing the net propagation speed and stratification-induced cross terms remaining small. Under intense stretch, positively curved flame elements exhibit larger displacement speeds, indicating a coupled effect of curvature, preferential diffusion and local radical transport. NO formation is dominated by fuel-nitrogen chemistry: HNO and NH₂ are the main NO-producing routes, whereas N₂ and N₂O provide the dominant NO-sink channels. The DNS predicts an outlet-averaged NO level of 400 dppm, while extended-domain RANS calculations indicate that longer residence times could reduce it below 100 dppm. Full article

The transition toward carbon-neutral energy systems has accelerated interest in hydrogen-fueled combustion technologies, where efficient fuel–air mixing is essential for stable and clean combustion. In the present study, the mixing characteristics of under-expanded supersonic jets injected into a pressurized environment are numerically investigated using validated computational fluid dynamics simulations. Two nozzle configurations are examined: a straight nozzle and sudden-expansion nozzles with different expansion ratios and expansion locations. The governing compressible flow equations are solved using the rhoCentralFoam solver with the SST k–ω turbulence model. The numerical framework is validated against Sod’s shock tube solution and experimental data for under-expanded supersonic free jets. The results show that sudden-expansion nozzles significantly modify the shock-wave structure, jet penetration, and lateral spreading compared with the straight nozzle. Among the investigated configurations, nozzles with intermediate expansion-section lengths exhibited pronounced Mach-disk oscillations with a dominant frequency of approximately 10 kHz. The normalized supersonic core length decreased from 17.79 for the straight nozzle to 5.50 for the best-performing sudden-expansion configuration, while the normalized jet half-width increased from 0.82 to 1.70, indicating substantially enhanced mixing performance. The findings demonstrate that nozzle geometry strongly governs the trade-off between flow stability and mixing enhancement in high-pressure supersonic jets. Full article

Focusing on the thermodynamic response of onboard liquid hydrogen tanks under dynamic sloshing conditions, this study investigates the flow-thermal coupling mechanism between the gas-phase space and the main chamber by establishing a numerical model that includes the gas-phase space. The results show that the gas-phase space enhances the initiative and efficiency of system pressure regulation through pressure-difference-driven mass transfer. The evolution of the gas–liquid two-phase temperature field sequentially undergoes four typical stages: pressure-difference-driven jet dominance, thermal stratification maintenance, turbulent mixing, and thermal stratification disappearance. The magnitude of the initial pressure difference significantly affects the temperature response and pressure equilibration time of the two chambers. The gas-phase space achieves thermal uniformity in approximately 4.1 s under sloshing, demonstrating its role as a “dynamic thermal buffer.” The research reveals the critical function of the gas-phase space in the dynamic thermal management of liquid hydrogen storage tanks, providing guidance for enhancing the safety and stability of the onboard hydrogen storage system. Full article

Exhaust piping in diesel engines is subject to severe thermal stress arising from high-temperature, high-pressure gas flows, and spray cooling with atomizing nozzles has become a widely adopted method to safeguard structural reliability. However, at present, the understanding of the spray fragmentation mechanism of two-phase flow under low inlet pressure is still not comprehensive. This study establishes a three-dimensional model of a gas–liquid impinging-jet nozzle and applies a coupled Volume-of-Fluid to Discrete-Phase-Model (VOF–DPM) approach to resolve the liquid breakup process in detail. High-speed imaging experiments were carried out to validate the numerical results. Orthogonal tests were conducted at five pressure levels for both gas and water—0.28, 0.24, 0.20, 0.16, and 0.12 MPa—producing 25 data pairs of spray cone angle and Sauter Mean Diameter (SMD). Within the 0–0.3 MPa air inlet pressure range explored here, raising the pressure consistently reduced the SMD and widened the cone angle, although both trends weakened as the pressure increased. Water inlet pressure exhibited a nonlinear influence, with local extrema appearing in the higher-pressure region. The overall SMD reached a minimum of 34.12 μm and a maximum of 149.04 μm. Using these 25 data points, a genetic algorithm was employed to optimize the pressure ratio under the constraint of total hydraulic power, yielding optimization strategies for different power budgets. An additional outcome of the simulation was the identification of a structural weakness: by reshaping the original flat impingement surface into a full conical surface, atomization quality improved by 29.36% under identical boundary conditions. These findings clarify the atomization mechanism of gas–liquid impinging jets under low inlet pressure and offer practical guidance for nozzle optimization. Full article