Search Results (1,772)

The use of Computational Fluid Dynamics (CFD) with surrogate-based optimisation is increasingly becoming common in the design of fluid delivery systems although there are very few cases where it has been applied to fixed water-based fire suppression systems. This paper seeks to propose an integrated four-stage engineering methodology incorporating field experiment, internal flow CFD using the Shear Stress Transport (SST) k-ω turbulence model in ANSYS Fluent, coherent-stream trajectory analysis and response surface methodology based on third-order polynomial regression. The proposed method is used to design the GS Mark III which is a fixed sprinkler nozzle system used to extinguish subsurface smouldering peatland fires. The validation of the coupled CFD and trajectory analysis model for 3, 5, and 7 bar using the field measurement shows the error of the model ranging from 2.55 to 3.58%. The coherent-stream trajectory is modelled by direct integration of the equations of motion, with aerodynamic deceleration represented by a single lumped coefficient calibrated against the field data, since neither a bluff-body drag coefficient nor a skin-friction closure reproduces the measured reach. The design of a parametric model involving 20 nozzle geometries in terms of diameter (5–15 mm) and discharge angles (0–67.5°) yields a surrogate with R² = 0.988, a root mean square error (RMSE) of 1.19 m and a mean absolute error (MAE) of 0.92 m. The surrogate locates the optimum at a diameter of 15 mm and a discharge angle of 38.26°, although the fitted response is flat between approximately 31° and 46°, so any angle within that band performs equivalently within the resolution of the model. The CFD simulation of the optimum (exit velocity = 32.121 m/s) gives a coherent-stream jet distance of 46.91 m, within 1.01% of the surrogate prediction. This represents a 25.9% improvement over the baseline configuration within the same modelling framework (37.25 m against 46.91 m), obtained at 2.28 times the baseline discharge, which the water supply must be able to sustain. Full article

Hydrogen-rich off-gas generated during nuclear fuel fabrication requires safe oxidation with limited nitric oxide (NO) formation. This study experimentally investigates the combustion of a simulated H₂/N₂ off-gas under open-air jet and CH₄ hot coflow-assisted conditions with MILD-like characteristics. One-dimensional premixed flame calculations are further employed to examine the intrinsic kinetics of H₂ oxidation and NO formation. Under the open-air baseline condition, the residual H₂ and NO concentrations measured at the flame tip were 244.8 and 158.1 ppm, respectively. Introducing hot coflow elongated the visible reaction zone from 13.0 cm to 15.0–22.0 cm and reduced the flame temperature from 783.6 °C to 405–517 °C. The residual H₂ concentration decreased to 30.7–104.3 ppm, while NO emissions decreased to 9.4–50.2 ppm. Kinetic analysis revealed that hydrogen oxidation was primarily governed by chain branching reactions involving H radicals and oxygen molecules. Increasing the hot coflow equivalence ratio altered the relative contributions of the Nitrogen–Nitrogen–Hydrogen (NNH) and Zeldovich-related NO formation pathways. Overall, the hot coflow was associated with an extended reaction zone as well as with reduced residual H₂ and NO concentrations under the investigated conditions. Full article

The long-pressure and short-exhaust ventilation method can effectively reduce dust concentration in mine roadways (tunnels) and alleviate hazards to workers. However, it is usually difficult to resolve the problem of high dust concentrations at the driver operation area. Accordingly, this paper proposes an air curtain dust isolation device suitable for the driver operation area, and computational fluid dynamics (CFD) methods were also employed to carry out numerical simulations and parameter optimization of its dust isolation efficiency. The research findings indicate that the device creates a transparent air curtain in front of the driver, effectively preventing dust from spreading towards the driver operation area. However, its dust isolation performance was significantly affected by the jet velocity. When the jet velocity was within the range of 0–10 m/s, the dust concentration at the driver operation area increased as the velocity rose; when the jet velocity increased to 15 m/s, the dust concentration fell sharply, with the average concentrations of total dust and PM_2.5 reaching the lowest values of 9.52 mg/m³ and 3.87 mg/m³, respectively. However, when the jet velocity was further increased to 20 m/s, the dust concentrations rose significantly again. Compared with conditions without an air curtain, at the optimum jet velocity of 15 m/s, the dust isolation efficiency reached 58.1%, indicating that this device can effectively safeguard the driver’s occupational health. The findings of this study may serve as a reference for dust protection at the driver operation area in similar working environments, such as tunnel excavation and metal mining. Full article

In recent decades, high-precision processing with ultrashort laser pulses has been progressively applied in highly efficient surface modification technologies for new multilayer nanomaterials widely used in industry. In this work, the ultrafast dynamics of layer-by-layer ablation of a multilayer Ni/Al thin-film at the initial stage (0–120 ps) after irradiation with a single 60 fs Gaussian-shaped femtosecond laser pulse, together with the morphology of the modified surface, were investigated using single-shot spatiotemporal resolved interferometry. Partial removal of the 46 nm thick upper Ni layer took place in the spallation mode with an expansion velocity of several hundred meters per second. The lower spallation threshold observed relative to bulk Ni is attributed to interference of rarefaction waves, reflected from the layer boundaries. A jet-like strong ejection of material during the complete removal of the upper nickel layer in the phase explosion mode was accompanied by an explosive expansion of the underlying overheated molten aluminum. The experimental study was supported by calculations of the spatiotemporal behavior of temperature in thin-film layers. The obtained results may help in studying the ablation mechanism of multilayer thin-films, as well as in developing simulation methods and laser processing technologies. Full article

Water-based suppression systems are widely employed in fire safety engineering, yet the accurate CFD modelling of their interaction with fire-driven flows remains a significant challenge. This study evaluates the impact of drag force modelling and grid mesh resolution on interaction boundary height predictions between a hot air jet at experimental velocities of 3.3, 4.2, and 5.3 ms⁻¹ and a full-cone 30° water spray nozzle operating at 0.084 LPM using the Fire Dynamics Simulator (FDS 6.9.1), employing the Very Large Eddy Simulation (VLES) turbulence simulation mode with the Deardorff subgrid-scale and WALE near-wall turbulence models. Gas phase and water spray simulations were independently validated against the experimental measurements of Zhou, with the water spray study establishing that representative Lagrangian particles must be on the order of 10⁵ to avoid spurious zero readings in far-field measurements. Interaction phase modelling was conducted using mesh cell sizes of 4 mm and 2 mm with a localized drag reduction approach, confirmed to operate within the LES regime through an a posteriori turbulence resolution assessment. The results demonstrate that improved drag physics combined with refined grid resolution yields meaningful improvements in the predicted interaction boundary height, highlighting the importance of addressing both aspects concurrently for reliable multi-phase flow predictions in FDS. Full article

Conventional air stripping for ammonia–nitrogen wastewater is often hampered by packing clogging and low mass transfer efficiency. To address these limitations, this study proposes a jet impact negative pressure reactor (JI-NPR) featuring an optimized scatter-pattern (D7) multi-orifice configuration. Computational Fluid Dynamics (CFD) simulations were employed to systematically investigate the effects of Reynolds number (Re = 5503.4~9651.0, corresponding to 2.76~4.84 m/s) on the hydrodynamic characteristics and deamination performance. Results indicate that increasing jet velocity significantly enhances the water volume fraction, resultant velocity, and pressure core intensity within the impact zone. Notably, these enhancements are maximized at the second row (z = 146 mm), attributed to reduced interference from the negative-pressure flash evaporation region. While a higher Re promotes interfacial renewal and vortex evolution, thereby enhancing mass transfer, it also intensifies energy dissipation and reduces the uniformity of the turbulent kinetic energy distribution. This work elucidates a critical trade-off between mass transfer enhancement and energy consumption, establishing a quantitative structure: the Re–flow field-performance relationship. The findings provide a theoretical foundation for the design and optimization of energy-efficient, high-performance wastewater treatment systems. Full article

Microquasars are candidate sites for high-energy particle production within our galaxy. Because their distances and compact emission regions limit direct observational constraints, numerical simulations are useful for connecting jet dynamics with possible multi-messenger signatures. This work models neutrino production from relativistic magneto-hydrodynamic microquasar jets, focusing on the proton–photon ($p\gamma$) channel associated with interactions between accelerated protons and ambient photon fields. Proton–proton ($pp$) interactions are acknowledged as a possible process in dense environments, but they are not modeled in the present calculation. A ray-tracing procedure is applied to the hydrodynamic simulation output to produce synthetic neutrino images from a stationary observer’s perspective. Synthetic spectra and intensity maps are presented and compared with representative sensitivities of current and future neutrino detectors. Full article

A jet grout design beneath raft foundations requires simultaneous selection of column geometry while satisfying bearing resistance and settlement criteria. This study develops a physics-generated artificial neural network (ANN) surrogate for performance-based screening of discrete jet grout configurations in soft to medium clays. Six engineering variables—undrained shear strength, constrained modulus, raft pressure, column diameter, spacing, and length—were used to generate 12,000 analytical cases representing 400 geometries. Equivalent ultimate column-grid pressure and settlement were calculated using established resistance formulations and an equal strain composite settlement model, respectively. Complete geometry groups were separated into training, validation, and independent test subsets to prevent information leakage, and a compact 6–24–12–2 ANN was trained to predict both responses simultaneously. For 2400 independent test cases representing 80 previously unseen geometries, the ANN achieved R² values exceeding 0.95 for both outputs and identified the same minimum-intensity feasible configuration as the analytical procedure in the illustrative design application. Independent three-dimensional finite-element simulations provided a complementary numerical assessment of representative settlement responses. The proposed framework integrates source-traceable analytical formulations, multi-output surrogate prediction, and performance constraints into a transparent preliminary design methodology for rapid screening of jet grout configurations. More broadly, it demonstrates how physics-generated machine learning surrogates can support the transition towards data-driven geotechnical design by systematically linking multidimensional engineering inputs with performance-based design decisions. Full article

Water-jet guided laser (WJGL) technology has gained significant attention in precision manufacturing due to its extremely small heat-affected zone. However, laser-induced water breakdown severely constrains the achievable laser power and processing efficiency. This paper presents and validates an optical solution employing a custom-designed rotationally symmetric aspheric lens. The lens is designed to generate a sequence of discrete focal points distributed along the optical axis. This configuration maintains a high average laser power while suppressing the peak power density at each individual focus below the water breakdown threshold. Theoretical modeling and ray tracing simulations confirm the superior performance of the lens in creating a controllable multi-focal beam. Experimental results demonstrate that a WJGL system incorporating the six-focus aspheric lens operates stably at 350 W. This represents a 300 W increase compared to the conventional spherical lens, which had a stable operating power limit of approximately 50 W within this experimental system. In microgroove machining experiments on NiTi alloy, the new system achieved an approximately 3.5-fold increase in groove depth and a 2.7-fold reduction in taper angle. This study provides a practical and effective beam shaping strategy to overcome the fundamental power limitation in WJGL technology. Full article

A water–steam ejector can be used for steam exhausting in some equipment, such as sterilization systems in hospital facilities. In this type of ejector, a water jet in the center is used to entrain and transport steam from the sterilization chamber. The performance of the ejector, which is a function of the pressure in the sterilization chamber and the temperature of the water, is crucial for the reduction in water and energy consumption. The numerical simulation of this type of device is challenging because of the mass, momentum and energy exchange between the phases. In this study, numerical simulations of an axisymmetrical model of a water–steam ejector considering mixing and heat and mass transfer by condensation are shown. The Euler–Euler method with OpenFOAM v2312 was used. The influence of the steam-bubble diameter was studied, and the results were validated with a previously published experimental report, which showed an agreement of approximately 2.5% for the adopted mesh size. The proposed solution may be appropriate for rapid design procedures for these types of devices. Full article

Adaptive and multi-functional nozzle actuation is highly demanded for modern aero-propulsion systems. Realizing integrated thrust vectoring, variable exit-area adjustment and reverse-thrust generation within a compact layout still poses substantial challenges. Inspired by archerfish’s integrated flow-regulation mechanism, which relies on coordinated oral bones and muscles to generate asymmetric oral deformation for jet shaping, direction control and flow-passage switching, this paper develops a nozzle actuation mechanism drawing on the kinematics of the archerfish jaw-operculum system. The design integrates pitch vector adjustment, variable exit-area modulation (full-closure included), and reverse-thrust generation. A single electric-cylinder-linkage assembly drives the nozzle exit, while lead-screw actuators govern the operculum-mimicking flow-diversion structure for reverse-thrust switching. Validated by kinematic analysis and three-dimensional flow-field simulations, the mechanism delivers a maximum continuous geometric pitch deflection of 36° within 8 s and stepless exit-area adjustment ranging from 1.8 × 10⁴ mm² to full closure. It enables active modulation of jet mixing behaviours and reverse-thrust output for landing deceleration. Compared with conventional nozzles, this bionic configuration achieves a streamlined actuation layout, competitive vectoring performance, continuous area adjustability and reduced control complexity, offering an innovative bionic solution for adaptive aero-propulsion devices. Full article

This study presents a 3D computational fluid dynamics (CFD) investigation of methane and methanol combustion in a medium-speed, large-bore marine spark-ignition engine equipped with a pre-chamber (PC) ignition system. Simulations were performed in ANSYS Forte at 100%, 80%, and 20% engine load. Methane operation with an active PC was used as the reference configuration, while methanol was investigated with both active and passive PC. A preliminary injection-timing analysis was conducted for the active methanol configuration to obtain a near-stoichiometric and sufficiently homogeneous mixture inside the PC at spark timing (ST). The results show that active methanol operation promotes earlier heat release, shorter combustion duration, and higher thermal efficiency than methane operation. The active PC generates stronger turbulent reacting jets and ensures more robust combustion than the passive configuration. Methanol also considerably reduces NO_x emissions because of its lower initial and combustion temperatures. However, active methanol operation increases CO emissions, particularly at low load, because of incomplete oxidation associated with low temperatures, mixture inhomogeneity, and possible spray–wall interaction. The passive PC further reduces NO_x and CO emissions but causes delayed combustion, lower thermal efficiency, higher fuel consumption, and tank-to-wake CO₂ emissions than the active methanol configuration. Full article

Forced spray on transmission gears performs the triple functions of lubrication, heat dissipation, and tooth surface cleaning under high-speed and heavy-duty conditions, serving as a key technical means to prevent scuffing, pitting, or even tooth breakage failure and ensure highly reliable operation of the transmission system. This study conducted numerical simulations using CFD to investigate the lubrication performance of high-speed spur gear pairs with respect to nozzle parameters including jet velocity, nozzle position, included angle, length, and number of nozzles. The results show that the medium jet velocity of 40–60 m/s achieves an optimal balance between penetration depth and spray dispersion. The results indicate that a medium jet velocity of 40–60 m/s optimally balances penetration depth and spray dispersion. Dual-nozzle oil injection significantly improves spatial uniformity and establishes a stable circular recirculation structure, increasing the oil volume fraction in the meshing zone by approximately 40% compared to the single-nozzle configuration, and reducing the area of dry patches by over 60%. A nozzle inclination angle of 60–90° combined with a length of 30 mm yields the best combination of oil delivery and coverage. Furthermore, upgrading from a 2 + 1 to a 3 + 1 nozzle layout enhances oil film continuity and suppresses abrupt negative-pressure fluctuations during meshing, thereby stabilizing the hydrodynamic lubrication effect. These findings provide quantitative guidance for optimizing nozzle geometry and layout in high-speed gearbox lubrication systems, contributing to improved reliability and reduced energy loss. Full article

Fuel design based on distillation fractions is crucial for advancing fuel development and optimizing combustion systems. However, the chemical diversity and broad boiling-point distribution of full-range fuels pose significant challenges for kinetic modeling. In this study, a volatility-aware, multi-component kinetic mechanism was developed for simulating the combustion of various distillation fractions from an FRF in diesel engines. The mechanism comprises 261 species and 860 reactions. Unlike conventional surrogate mechanisms designed primarily for a single fuel or narrow distillation range, the proposed framework simultaneously represents the major hydrocarbon classes, ignition quality, and boiling-point distribution of FRF. The surrogate palette includes n-pentane, n-heptane, n-decane, n-dodecane, n-hexadecane, heptamethylnonane, 1-methylnaphthalene, iso-octane, methylcyclohexane, decalin, toluene, tetralin, and 1,2,4-trimethylbenzene. These components were selected to reproduce the molecular structures, ignition characteristics, and distillation behavior of the target fuel fractions. The mechanism was further refined through targeted replacement of the toluene sub-mechanism using updated hydrogen-abstraction and benzyl-radical oxidation reactions, followed by a fuel-oriented five-stage reduction strategy involving reaction-pathway-based pruning, DRGEP reduction, isomer lumping, sensitivity/ROP refinement, and targeted rate optimization. The resulting mechanism provides reasonable predictions of ignition delay, laminar flame speed, and species profiles for pure components, surrogate fuels, and real gasoline, jet, and diesel fuels. Coupled with a three-dimensional CFD model, the reduced mechanism also reproduces the main combustion phasing, pressure-rise process, and peak in-cylinder pressure of a diesel engine at 500 and 800 r/min over the investigated intake-temperature range. Although discrepancies remain in the low-temperature/negative-temperature-coefficient regime and in the quantitative prediction of the peak apparent heat-release rate, the mechanism provides a unified and practical framework for linking FRF distillation characteristics with chemical reactivity and engine-level combustion behavior. It therefore offers a foundation for designing tailored fuels from distillation fractions for operation in extreme environments. Full article

Short-circuit flow severely degrades cyclone separation, yet its influence zone has not been clearly defined. In this work, the Reynolds stress model (RSM) was adopted to perform numerical simulations for a 300 mm PV-type cyclone separator, and the simulation results were validated against published tangential-velocity experimental data. The radial velocity along the extension lines of the vortex finder’s inner wall was analyzed to define the short-circuit flow influence zone, and a sector-resolved intensity index was proposed to quantify its circumferential non-uniformity. The results show that the lower boundary of the influence zone is a circumferentially varying curved surface rather than a horizontal plane. Among the four sectors, the 180–270° sector exhibits the greatest penetration depth (55 mm) and the highest inward radial velocity (−15.45 m/s). The proposed index indicates that Sector III contributes 38.7% of the total short-circuit flow intensity, and the dimensionless index is 0.127 for the present case. Within the influence zone, the inward radial velocity peaks at Z = 12 mm and approaches zero by Z = 53 mm, while the tangential velocity increases from 4.22 to 57.13 m/s, indicating Rankine vortex development. The short-circuit flow is governed by the coupled effects of inlet jet squeezing, vortex-core displacement, and the interaction between upward and downward flows. The proposed influence-zone definition and intensity index provide a quantitative framework for describing short-circuit flow and may be useful for evaluating cyclone design and short-circuit-flow suppression strategies. Full article